TERMS IN THEORETICAL PHYSICS

Definition: The positive square root of the sum of the squares of the real number part and the imaginary number part of a complex number.

Related terms: none

Symbol: |z|

SI units: not applicable

Remarks:

The mathematical expression for the absolute value of a complex number is:

|z| = + [x² + y²]^1/2

where:

z = x ± iy

The absolute value of a complex number is also equal to the positive square root of the product of the complex number and its complex conjugate.

|z| = + [(x + iy)(x - iy)]^1/2

The definition of a complex number encompasses the definition of a real number.

absolute value of a real number

Definition: The value of the real number without regard to its sign.

Related terms: none

Symbol: |z|

SI units: not applicable

Remarks:

absolute zero

Category: fundamental constant

Definition: The lowest possible thermodynamic temperature.

Related terms: none

Symbol: 0 K

Values: 0 kelvin

Remarks:

At absolute zero, the thermal energy of a system is exactly zero.

In quantum mechanics, absolute zero is interpreted as the temperature at which all particles are in the lowest-energy quantum states available. Generally, the available quantum states do not have zero energy.

absorptance
absorption factor

Category: empirical constant

Definition: The ratio of the electromagnetic radiation incident upon a object to the electromagnetic radiation absorbed by the object.

Related terms: none

Symbol: α

SI units: dimensionless

Remarks:

absorption

Category: phenomenon

Definition:

A reduction in the flux of electromagnetic radiation passing through a medium.
The taking up of a fluid either into solution in a liquid or in the pores of a solid.

Related terms: adsorption

Symbol: not applicable

SI units: not applicable

Remarks:

accelerated reference frame
accelerating reference frame

Category: concept

Definition: A reference frame that is experiencing rotation or rectilinear acceleration or both.

Related terms: inertial reference frame

Symbol: not applicable

SI units: not applicable

Remarks:

acceleration
linear acceleration

Category: vector quantity

Definition: The rate of change of velocity with respect to time.

Related terms: angular acceleration, deceleration

Symbol: a

SI units: meters / second²

Remarks:

Negative acceleration is called deceleration.

The term acceleration is applied to both rectilinear velocities and angular velocities.

An acceleration may be due to an increase or decrease in speed or to a change in direction.

acceleration of gravity

Category: vector quantity

Definition: The acceleration of a object due to a gravitational field.

Related terms:

For a list of other related terms see: gravitation

Symbol: g

Values: 9.806 65 meters / second² (standard value)

Remarks:

acoustics

Category: branch of physics

Definition: The branch of physics that deals with the production, control, transmission, reception, and effects of sound.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

action

Category: scalar quantity

Definition: The product of a component of linear momentum (p_i) and the change in the corresponding positional coordinate (q_i).

Symbol: none

SI units: kilogram × meters² / second

Remarks:

This term is outmoded.

Category: ??

Definition: The reciprocal of impedance.

Related terms: electric admittance

Symbol: Y

SI units: varies

Remarks:

adsorption

Category: phenomenon

Definition: The adhesion of a thin layer of fluid to the surface of a solid.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

aggregate

Category: common term

Definition: A group of substances.

Related terms:

For a list of other related terms see: object

Symbol: not applicable

SI units: not applicable

Remarks:

algebra

Category: branch of mathematics

Definition: A generalization of arithmetic in which symbols (usually letters) representing numbers are combined according to the rules of arithmetic.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

algebraic expression

Category: mathematical expression

Definition: A mathematical expression with a finite number of terms, each term of which involves only constants and exponentiated variables.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The following is an algebraic equation:

y = ax^-2 + bx^-1 + c + dx + ex²

All the terms in the following mathematical expression are non-algebraic:

sin(x) + e^x + ln(x)

alpha particle

Category: particle

Definition: The nucleus of a helium (⁴He) atom.

Related terms: particle

Symbol: α

SI units: not applicable

Remarks:

alpha radiation

Category: phenomenon

Definition: A stream of alpha particles.

Related terms: beta radiation, gamma radiation

Symbol: not applicable

SI units: not applicable

Remarks:

Alpha radiation is ejected by many radioactive elements.

alternating current
alternating electric current

Category: scalar quantity

Definition: An electric current that periodically reverses its direction.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: I

SI units: amperes = coulombs / second

Remarks:

An alternating electric current is usually substantially constant in amplitude.

alternating current circuit

Category: concept

Definition: A continuous loop along which an alternating electric current does or may flow.

For a list of other related terms see: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

amount

Category: common term

Definition: The number resulting from the counting or measuring of a quantity.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

amount of substance

Category: base quantity

Definition: The number of atoms or molecules of a specified substance divided by the Avogadro constant.

In other words, the number of moles of the substance.

Related terms: base quantities, molar

Symbol: n

SI units: moles

Remarks:

Amount of substance is a base quantity in the SI system of units.

ampere

Definition: The base unit of electric current in the SI system of units.

The ISO definition is: "The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2x10^-7 newton per meter of length." (1946)

Related terms: none

Symbol: A

SI units:1 ampere = 1 coulomb / second

Remarks:

Ampere's law

Category: law

Statement: The curl of the magnetic flux density at a point in a magnetic field is proportional to the volume current density at that point.

Related terms: Maxwell's equations

Symbol: not applicable

SI units: not applicable

Remarks:

In differential form, the mathematical expression of Ampere's law in free space is:

Ñ ´ B = μ₀ J

where:

J = volume current density

Integrating over a surface, we get:

By Stoke's theorem:

Thus, the integral form of Ampere's law is:

amplitude
peak value

Category: scalar quantity

Definition: The maximum absolute value of the magnitude of the displacement of an alternating quantity from its central value.

Related terms: none

Symbol: A

SI units: varies

Remarks:

This term is most commonly applied to sinusoidal motion.

angle
plane angle

Category: scalar quantity

Definition: A measure of the amount of turning necessary to bring a line or plane into coincidence with, or parallel to, another line or plane.

Related terms: degree of arc, minute of arc, second of arc, radian

Symbol: Ð

SI units: radians

Remarks:

angle of incidence

Category: scalar quantity

Definition: The angle between the path of a ray or an object striking a surface and the normal to the surface at the point of incidence.

Related terms: none

Symbol: not applicable

SI units: radians

Remarks:

angstrom

Definition: A unit of measurement of length.

Related terms: none

Symbol: Å

SI units: 1 angstrom = 10^-10 meter

Remarks:

This unit is convenient for atomic-scale lengths.

The use of this unit is discouraged.

angular acceleration

Category: pseudovector quantity

Definition: The rate of change of angular velocity.

Related terms: linear acceleration

Symbol: α

SI units: radians / second²

Remarks:

angular frequency

Category: scalar quantity

Definition: Of an periodic motion or periodic function, the product of the frequency and the factor 2π.

Related terms: angular velocity

Symbol: ω

SI units: radians / second = (cycles / second)(radians / cycle)

Remarks:

The mathematical expression for angular frequency is:

ω = 2πυ

where:

ω = angular frequency

υ = frequency

Angular frequency is mathematically equivalent to angular velocity.

The term angular frequency is used for oscillating systems. The term angular velocity is used for rotating systems.

angular momentum
moment of momentum
moment of momentum about an axis

Category: pseudovector quantity

Definition: The moment of linear momentum about an axis or point.

Symbol: L

SI units: kilogram × meters² / second

Remarks:

It is usually assumed that 1) the linear momentum lies in a plane perpendicular to the axis and 2) the intended quantity is the moment about the point of intersection of the plane and the axis. If this is not the case, see moment about an axis.

Under the above assumptions, the mathematical expression for angular momentum is:

L = r ´ p

where:

L = angular momentum

r = radius vector

p = linear momentum

Angular momentum due to a revolving motion is called orbital angular momentum.

Angular momentum due to a rotating motion is called spin angular momentum.

Angular momentum is a conserved quantity in all circumstances.

angular velocity

Category: pseudovector quantity

Definition: The rate at which a object rotates about an axis.

Related terms: angular frequency

Symbol: ω

SI units: radians / second

Remarks:

Angular velocity is mathematically equivalent to angular frequency.

The term angular frequency is used for oscillating systems. The term angular velocity is used for rotating systems.

anion

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

an isotropic
anisotropy

Category: quality

Definition:

Not isotropic.
Possessing or denoting a quantity that varies with direction.

Related terms: isotropic

Symbol: not applicable

SI units: not applicable

Remarks:

anthropic principle

Category: concept

Definition: The idea that the universe is like it is because, if it were not, we would not be here to observe it.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

anti symmetric

Category: concept

Definition: If a quantity changes sign under a mathematical operation, the quantity is said to be antisymmetric under the mathematical operation.

Related terms: symmetric

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

Angular momentum changes sign under a space inversion, therefore angular momentum is antisymmetric under a space inversion.

arbitrary

Category: concept

Definition:

Depending on choice or discretion.
Decided by custom or authority.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

arbitrary constant

Category: concept

Definition: A value that has been chosen as opposed to measured or determined by theoretical considerations.

Related terms:

For a list of other related terms see: constant

If y = f(x), then x is an argument.

arithmetic mean
mean
average

Definition: The sum of a set of numbers divided by their number.

Of a continuous function of one variable, the integral of the function between two values of the variable divided by the absolute value of the difference between the two values of the variable.

Related terms: geometric mean, median, mode

Symbol: not applicable

SI units: not applicable

Remarks:

The arithmetic mean of n numbers a₁ ,a₂ ,a₃ ,..., a_n is:

(a₁ + a₂ + a₃ + ... + a_n) / n

The arithmetic mean of a mathematical function of x is:

ò_a^b f(x) dx / (b-a)

Category: branch of physics

Definition: The study of the contents and behavior of the universe.

Related terms: astrometry, astrophysics, cosmology

Symbol: not applicable

SI units: not applicable

Remarks:

astrophysics

Category: branch of physics

Definition: The study of the physical and chemical constitution of extraterrestrial objects.

Related terms:

For a list of other related terms see: astronomy

Symbol: not applicable

SI units: not applicable

Remarks:

a symmetry

Category: concept

Definition: A violation of symmetry.

Related terms: symmetry

For a list of other related terms see: symmetry

Symbol: not applicable

SI units: not applicable

Remarks:

asymptotic

Category: concept

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

asymptotic freedom

Category: concept

Definition: A property of the strong interaction by which, at high energies (short distances), the strong force is weakened and quarks and gluons behave almost as free particles.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

at rest

Category: concept

Definition: If a object is not in motion with respect to an inertial reference frame, the object is said to be at rest with respect to the inertial reference frame.

Related terms:

For a list of other related terms see: motion, reference frame

Symbol: not applicable

SI units: not applicable

Remarks:

An object at rest with respect to one inertial reference frame may be in motion with respect to another inertial reference frame.

Since, by definition, an inertial reference frame is not accelerating, a object at rest with respect to an inertial reference frame cannot be accelerating. The same can be said of another inertial reference frame.

atmosphere

Category: phenomenon

Definition: The whole mass of air surrounding the earth.

Related terms: atmospheric pressure

Symbol: not applicable

SI units: not applicable

Remarks:

atmospheric pressure

Category: scalar quantity

Definition: The pressure at a point in the atmosphere.

Related terms: standard atmosphere, standard pressure

Symbol: not applicable

SI units: not applicable

Remarks:

Frequently, a standard atmosphere is intended.

Category: concept

Definition:

A straight line about which a object or system may rotate or revolve.
One of the reference lines of a coordinate system.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

azimuth

Category: scalar quantity

Definition: A horizontal direction expressed as the angular distance between the direction of a fixed point and the direction of an object.

Related terms: none

Symbol: ??

SI units: radians

Remarks:

Definition: A unit of measurement of pressure.

Related terms: none

Symbol: bar

Values: 1 bar = 10⁵ pascals

Remarks:

bare mass

Category: scalar quantity

Definition: The estimated mass of a quark that is not confined in a hadron.

Related terms: effective mass, quark confinement

Symbol: ??

SI units: kilograms

Remarks:

barn

Definition: A unit of measurement of area.

Related terms: none

Symbol: b

SI units: 1 barn = 10^-28 meter²

Remarks:

The barn is used for nuclear cross sections.

baryon
normal baryon
antibaryon

Category: category of particle

Definition: Baryon is a generic term for all particles that consist of exactly three quarks.

A normal baryon consists of three normal quarks.

An antibaryon consists of three antiquarks.

Related terms:

For a list of other related terms see: particle categories

Symbol: not applicable

SI units: not applicable

Remarks:

All baryons are composed of quarks and are therefore hadrons

Normal baryons have a baryon number of +1. Antibaryons have a baryon number of -1. All other particles have a baryon number of 0.

The most common baryons are the proton and the neutron.

baryon number
baryon quantum number

Category: quantum number

Definition: An additive quantum number associated with a quantized property of the elementary particles. Also the property itself.

Related terms: nucleon number, quantum number

Symbol: B

SI units: dimensionless

Remarks:

By definition, the particles have the following baryon numbers:

baryons	+1
antibaryons	-1
quarks	+1/3
antiquarks	-1/3
leptons	0
mesons	0
gauge bosons	0

Baryon number is conserved in all particle interactions.

The term baryon number can also be used to refer to the total number of baryons in the universe less the total number of antibaryons.

baryonic matter

Category: substance

Definition: Matter that consists of baryons.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

base
basis

Category: common term

Definition: A starting or reference point, line, plane, number, or amount.

Related terms: basic

Symbol: not applicable

SI units: not applicable

Remarks:

base line

Category: concept

Definition: A line serving as a base.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

base quantity

Category: concept

Definition: The ISO has adopted a system of units in which they define seven base quantities:

length
mass
time
electric current
thermodynamic temperature
amount of substance
luminous intensity

Related terms:

For a list of other related terms see: units of measurement

Symbol: not applicable

SI units: not applicable

Remarks:

The definitions of the base quantities are based upon actual physical measurements.

All other quantities in the SI system of units are defined in terms of the seven base quantities. These other quantities are called derived quantities. Important derived quantities include:

angular momentum
electric charge
energy
force
frequency
linear momentum
velocity
volume

The choice units of measurement to be basic units is somewhat arbitrary.

base unit of measurement
base unit

Category: concept

Definition: The unit of measurement assigned to a base quantity in a system of units.

In the SI system of units, the seven base quantities and their corresponding base units are:

base quantity	base unit
length	meter
mass	kilogram
time	second
electric current	ampere
thermodynamic temperature	kelvin
amount of substance	mole
luminous intensity	candela

In addition, the ISO has designated two "supplementary units of measurement". These may also be regarded as base units.

base quantity	base unit
angle	radian
solid angle	steradian

Related terms:

For a list of other related terms see: units of measurement

Symbol: not applicable

SI units: not applicable

Remarks:

For the ISO definition of an individual base unit see the individual unit.

basic

Category: common term

Definition:

Of central, essential, or underlying importance.
Serving as a base or starting point.

Related terms: base

Symbol: not applicable

SI units: not applicable

Remarks:

beat frequency

Category: phenomenon

Definition: The difference in frequency between two frequencies.

Related terms: none

Symbol: ??

SI units: hertz

Remarks:

beauty
bottomness

Category: quantized property

Definition: Beauty is a quantized property and an additive quantum number associated with quarks.

Related terms:

For a list of other related terms see: quarks

Symbol: b

Values: -1, 0, or +1

Remarks:

By definition, bottom quarks have a beauty of +1, bottom antiquarks have a beauty of -1, and all other elementary particles have a beauty of 0.

Beauty is conserved in all particle interactions except weak interactions.

Becquerel

Definition: The SI unit of ionizing radiation.

Related terms: curie

Symbol: Bq

Values: 1 Becquerel = 1 disintegration / second

Remarks:

Becquerel is preferred over curie.

beta particle
beta radiation

Category: particle

Definition: An electron or positron emitted by a nucleus when it decays.

Related terms: alpha radiation, gamma radiation

Symbol: not applicable

SI units: not applicable

Remarks:

Big Bang

Category: theory

Definition: A postulated, explosion-like, event that occurred about 10 to 15 billion years ago and from which the universe as we now know it has evolved.

Related terms: cosmology

Symbol: not applicable

SI units: not applicable

Remarks:

Big Crunch

Category: theory

Definition: A possible future, implosion-like, event in which the universe as we know it will end.

Related terms: cosmology

Symbol: not applicable

SI units: not applicable

Remarks:

binding energy

Category: scalar quantity

Definition: The amount of energy that would be required to separate particles that are bound together by forces of any sort (or the energy released when the particles combine).

Related terms: fusion

Symbol: E_B

SI units: electronvolts = newton × meters

Remarks:

The mass of a nucleus is slightly less than the mass of its constituent nucleons. This mass difference is equivalent to the energy released when the nucleons bind together.

binomial

Category: mathematical expression

Definition:

A mathematical expression consisting of two terms connected by a sign.
Consisting of two parts.

Related terms: binomial expansion

Symbol: a ± b

SI units: not applicable

Remarks:

binomial distribution

Category: mathematical expression

Definition: The expected probability distribution of events that have two equally likely and independent outcomes.

Related terms: normal distribution

Symbol: not applicable

SI units: not applicable

Remarks:

binomial expansion

Category: mathematical operation

Definition: The expansion into an infinite series of the mathematical expression (1+x)ⁿ.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of the binomial expansion is:

where |x| < 1 and n is any real number.

This mathematical operation is often used to obtain an approximation of a quantity.

Examples:

Relativistic kinetic energy is given by:

K = mc²(γ-1)

where:

m = rest mass

Here x = -(v / c)² and n = -1/2. The first three terms are:

K =

If v << c then:

K = mv²/2

Biot-Savart law

Category: law

Statement: The magnetic flux density produced by a steady electric current moving in a long straight conductor is directly proportional to the electric current and inversely proportional to the distance of the point of observation from the conductor.

Related terms: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of the Biot-Savart law is:

B = μ₀I / 2πz

where:

B = magnetic flux density at a point

I = line current

z = distance from conductor to point

Category: phenomenon

Definition: A shift in the wavelength of electromagnetic radiation toward shorter wavelengths.

Related terms: Doppler effect, redshift

Symbol: not applicable

SI units: not applicable

Remarks:

Blueshift can be measured from the displacement of spectral lines.

Blueshift in electromagnetic radiation from nearby extraterrestrial objects is due primarily to their motion toward from the earth.

Bohr magneton

Category: property

Definition: The intrinsic magnetic moment of an electron.

Related terms: nuclear magneton

Symbol: μ_B

Values: 9.2740 × 10^-24 joules / tesla

Remarks:

Bohr model
Bohr theory

Category: hypothesis

Definition: An enhancement of the Rutherford model. The Bohr model postulates that the electrons orbit the nucleus at various levels and that the energy differences between the levels are quantized.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Bohr radius

Category: fundamental constant

Definition: The radius of a hydrogen atom calculated on the basis of the Bohr model.

Related terms: none

Symbol: a₀

Values: 1 Bohr radius = 5.2918 × 10^-9 meters

Remarks:

The Bohr radius is the radius of the supposedly circular orbit of an electron.

The mathematical expression for the Bohr radius is:

where:

m = mass of an electron

e = charge of an electron

boiling point

Category: property

Definition: The temperature at which a liquid vaporizes.

Related terms: freezing point

Symbol: not applicable

SI units: kelvin

Remarks:

If the pressure is not specified, standard pressure is assumed.

Boltzmann constant

Category: fundamental constant

Definition: The ratio of the molar gas constant to the Avogadro constant.

Related terms: none

Symbol: k

Values: 1.380 658 × 10^-23 joules / kelvin

Remarks:

The product kT, where T is the thermodynamic temperature, occurs frequently in statistical mechanics. It (kT) has the units of energy and is called the thermal energy.

bond

Category: phenomenon

Definition: A force holding two objects together.

Related terms: chemical bond, covalent bond, ionic bond

Symbol: not applicable

SI units: not applicable

Remarks:

Bose condensation
Bose-Einstein condensation

Category: phenomenon

Definition: A phenomenon that occurs at low temperatures in systems consisting of large numbers of bosons in which a significant fraction of the particles occupy a single quantum state.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

In contrast, fermions are prohibited by the Pauli exclusion principle from occupying the same quantum state.

Bose-Einstein statistics

Category: ??

Definition: A statistical description of quantum mechanical systems in which there is no restriction on the way in which particles can be distributed over the individual energy levels.

Related terms: Fermi-Dirac statistics

Symbol: not applicable

SI units: not applicable

Remarks:

The type of statistics that apply to a particle is determined by the spin of the particle:

statistics	spin	particle category
Fermi-Dirac statistics	odd half integer	fermions
Bose-Einstein statistics	integer	bosons

boson

Category: category of particle

Definition: A generic term for all particles that have integer spin.

Related terms:

For a list of other related terms see: particle categories

Symbol: not applicable

SI units: not applicable

Remarks:

All particles are either:

bosons, that have integer (0, 1, 2, ...) spin, or
fermions, that have odd half integer (1/2, 3/2, ...) spin.

There are two categories of bosons:

gauge bosons and
mesons

The distribution of bosons over the individual energy levels of a system is not restricted by the Pauli exclusion principle and therefore bosons obey Bose-Einstein statistics.

The wave function for a set of identical bosons must be completely symmetric under permutations of the particles.

boson field
gauge boson field

Category: generic term

Definition: A field associated with a particular gauge boson.

Related terms:

For a list of other related terms see: field

Symbol: not applicable

SI units: not applicable

Remarks:

Each gauge boson has a corresponding field.

bottom quark
bottom antiquark

Category: elementary particle

Definition: One of the six flavors of quarks.

The properties of a bottom quark are:

property	value
generation	3rd
bare mass	~4200 MeV/c²
effective mass	~4700 MeV/c²
electric charge	-1/3
spin	1/2
beauty	+1

Related terms: beauty

For a list of other related terms see: quarks

Symbol: b

SI units: not applicable

Remarks:

The bottom quark has also been called the beauty quark.

boundary layer

Category: phenomenon

Definition: A layer of fluid lying next to a object that is in motion with respect to the fluid or vice versa.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Boyle's law

Category: law

Statement: If a given amount of gas is compressed at constant temperature, the volume of the gas is inversely proportional to the pressure.

Related terms: equation of state, ideal gas

Symbol: not applicable

SI units: not applicable

Remarks:

Boyle's law is only approximately true for actual gases.

branch of mathematics

Category: generic term

Definition: A specific subject in mathematics.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The branches of mathematics include:

algebra
analytic geometry
arithmetic
calculus
calculus of variations
differential equations
geometry
group theory
number theory
probability theory
statistics
topology
trigonometry
...

branch of physics

Category: generic term

Definition: A specific subject in physics. These include:

astronomy
atomic physics
classical mechanics
cosmology
electricity and magnetism
experimental physics
fluid mechanics
nuclear physics
optics
particle physics
periodic motion
quantum mechanics
relativity
statistical mechanics
string theory
theoretical physics
thermodynamics
systems of measurement

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

branch of science

Category: generic term

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

branching

Category: concept

Definition: The occurrence of competing decay processes in the disintegration of a nuclide.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

breaking point
ultimate strength

Category: property

Definition: The stress in an object or substance that has been elongated to the point of breaking.

Related terms: none

Symbol: not applicable

SI units: pascals = newtons / meter²

Remarks:

bremsstrahlung

Category: phenomenon

Definition: Electromagnetic radiation produced when a particle with an electric charge decelerates.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

broken symmetry

Category: concept

Definition: The apparent violation of a symmetry.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

It is thought that such violations are due to spontaneous symmetry breaking.

Brownian motion

Category: phenomenon

Definition: The irregular motion of small particles suspended in a fluid that is caused by the impact of molecules of the fluid.

Related terms: motion

Symbol: not applicable

SI units: not applicable

Remarks:

Btu
British thermal unit

Definition: The amount of energy required to raise the temperature of one pound of water at standard temperature and standard pressure one degree Fahrenheit.

Related terms: calorie

Symbol: Btu

SI units: 1 Btu = 1055.06 joules

Remarks:

Category: mathematical operation

Definition: A mathematical operation on the coordinates and momenta describing the state of a classical dynamics system that leaves the canonical (Hamiltonian function) form of the equations of motion unchanged.

Related terms: Hamilton's equations of motion

Symbol: not applicable

SI units: not applicable

Remarks:

capacitive reactance

Category: quantity

Definition: In an alternating current circuit, that part of electric impedance that is caused by electric capacitance.

Related terms: inductive reactance

For a list of other related terms see: electric impedance

Symbol: X_C

SI units: ohms = newton × meter × seconds / coulomb²

Remarks:

The mathematical expression for capacitive reactance is:

X_C = 1 / 2π×f×C

where:

X_C = capacitive reactance

f = frequency of the electric current

C = electric capacitance

cardinal number

Category: concept

Definition: The positive integers and zero.

Related terms: ordinal number

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

0, 1, 2, 3, ...

Cartesian coordinate system
Cartesian coordinate
Cartesian

Category: concept

Definition: A coordinate system formed by three mutually perpendicular axes through a point.

Related terms:

For a list of other related terms see: coordinate systems

Symbol: not applicable

SI units: not applicable

Remarks:

Usually the axes are labeled x, y, and z

The axes are fixed in the reference frame.

The coordinate system may be either right-handed or left-handed.

The coordinate system is right-handed if it satisfies the right-hand rule when the x-axis is rotated toward the y-axis through the smaller angle; otherwise it is left-handed.

Cartesian space

Category: concept

Definition: A space in which positions are specified in Cartesian coordinates.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

category of particle
particle category

Category: concept

Definition: A set of particles that have one or more common characteristics.

Related terms:

For a list of other related terms see: particle

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

General terms:

matter	normal matter	antimatter	ordinary matter
particles	normal particles	antiparticles	ordinary particles
elementary particles	...	...	...

Leptons

charged leptons	electron	muon	tauon
antileptons	positron	antimuon	antitauon
neutrinos	electron neutrino	muon neutrino	tauon neutrino
antineutrinos	electron antineutrino	muon antineutrino	tauon antineutrino

Quarks

...	up quark	charmed quark	top quark
...	up antiquark	charmed antiquark	top antiquark
...	down quark	strange quark	bottom quark
...	down antiquark	strange antiquark	bottom antiquark

Gauge bosons:

gluons	photons	gravitons	higgs bosons
intermediate vector bosons	W+ boson	W- boson	Z0 boson

Other composite categories

hadrons	bosons	fermions	mesons
...	...	...	...

Baryons

ordinary particles	proton	neutron	...
delta particles	...	...	...
lambda particles	...	Λ	Λ⁺
sigma particles	Σ^-	Σ⁰	Σ⁺
xi particles	Ξ^-	Ξ⁰	...
omega particles	...	Ω^-	...

pseudoscalar mesons

B⁺	B^-	B⁰	B⁰
D⁺	D^-	D⁰	D⁰
D_s⁺	D_s^-	...	...
K⁺	K^-	K⁰	K⁰
π⁺	π^-	π⁰	...
η	η'	η_c	...

Vector mesons

ρ	K*	ω	φ
J/ψ	D*	Υ	...

cation

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

celestial

Category: common term

Definition: Outside the immediate vicinity of the earth.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

celestial mechanics

Category: branch of physics

Definition: The study of the relative motions of systems of objects associated by gravitational fields.

Related terms: classical mechanics

Symbol: not applicable

SI units: not applicable

Remarks:

celestial object

Category: object

Definition: An object in the universe outside the immediate vicinity of the earth.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Celsius
Celsius scale
degree Celsius

Definition: A temperature scale having 0 as the freezing point of water and 100 as the boiling point of water at standard pressure.

Related terms: Fahrenheit, kelvin

Symbol: ºC

SI units: kelvin

Remarks:

One degree Celsius is equal to 1 degree kelvin.

center of mass
center of gravity
center of inertia

Category: concept

Definition: That point of a object or system of objects that moves as though the total mass of the system existed at the point and all external forces were applied at the point.

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

centi meter

Definition: One one-hundredth of a meter.

Related terms: inch

Symbol: cm

SI units: 1 centimeter = 10^-2 meter

Remarks:

central force field

Category: concept

Definition: A spherically symmetric force field , that produces a force on a particle that depends only on its distance from the center and is always directed radially.

Related terms:

For a list of other related terms see: inverse square law, field

Symbol: not applicable

SI units: not applicable

Remarks:

Examples: gravitational field, electric field

centrifugal

Category: concept

Definition: Acting in a direction away from the center or axis.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

centrifugal force

Category: pseudovector quantity

Definition: A pseudoforce on a object revolving about an axis that is equal and opposite to the centripetal force.

Related terms:

For a list of other related terms see: force

Symbol: ??

SI units: newtons

Remarks:

Category: system of units

Definition: A system of units having the centimeter, the gram, and the second as base units.

Related terms:

For a list of other related terms see: systems of units

Symbol: not applicable

SI units: not applicable

Remarks:

There are several variations of the cgs system of units:

cgs electromagnetic system of units
cgs electrostatic system of units
Gaussian system of units
Heaviside-Lorentz system of units

The cgs system of units has been generally superseded by the SI system of units however the cgs system of units, particularly the variation called the Gaussian system of units, is still used in some contexts.

chaos theory

Category: theory

Definition: A theory that deals with the behavior of systems that are so sensitive to the initial conditions of the system or contains such a large number of particles that the future state of the system can not be predicted.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

In such a case the behavior of the system cannot be distinguished from a random process even though it may be deterministic in a mathematical sense.

charge

Category: quantized property

Definition: A quantized property of particles that produces a force field .

There is a one-to-one correspondence between charges and the fundamental forces.

charge	fundamental force
color	strong force
electric charge	electromagnetic force
mass	gravitational force
weak charge	weak force

Related terms: interaction

Symbol: not applicable

SI units: varies

Remarks:

The term charge is often used when electric charge is the intended meaning. In this glossary, we intend always to use the more specific term.

In classical physics, the only charge that is dealt with is the electric charge and the term charge implies electric charge. In modern physics is probably best to be specific and use the complete term such as electric charge.

A charge does not exist independent of matter; it is always associated with a particle of matter.

charge conjugate

Category: concept

Definition: If one particle is identical to a another particle except that the signs of all the internal quantum numbers are changed, then the first particle is said to be the charge conjugate of the other particle and vice versa.

Related terms: antiparticle

Symbol: not applicable

SI units: not applicable

Remarks:

The charge conjugate of a normal particle is its antiparticle and vice versa.

In some cases, the charge conjugate of a particle is identical to the original particle.

charge conjugation

Category: mathematical operation

Definition: The mathematical operation of changing the sign of all of the internal quantum numbers of a particle while leaving all other properties unchanged.

Related terms: antiparticle, normal particle

Symbol: C

SI units: not applicable

Remarks:

Charge conjugation changes normal particles to antiparticles and vice versa.

charge conjugation parity
charge parity
C parity

Category: quantum number

Definition: A quantum number associated with charge conjugation. If the wave function changes sign under charge conjugation, C = -1; if it does not, C = +1.

Related terms: none

Symbol: C

Values: -1 or +1

Remarks:

Charge conjugation parity is conserved in all particle interactions.

charged lepton
charged antilepton

Category: category of particle

Definition: Charged lepton is a generic term for elementary particles that are leptons and have an electric charge.

The charged leptons are: the electron, the muon, the tauon and their antiparticles.

Related terms:

For a list of other related terms see: particle categories

Symbol: e, μ, τ

SI units: not applicable

Remarks:

Leptons can be divided into charged leptons and neutrinos.

Neutrinos are not charged leptons because they do not carry an electric charge.

Charles's law

Category: law

Statement: The volume of a fixed amount of gas is directly proportional to the absolute temperature of the gas when the pressure is kept constant.

Related terms: Boyle's law, Gay-Lussac's law, ideal gas

Symbol: not applicable

SI units: not applicable

Remarks:

Charles's law is only approximately true for actual gases.

charm

Category: quantized property

Definition: Charm is a quantized property and an additive quantum number associated with quarks.

Related terms: quarks

Symbol: c

Values: -1, 0, or +1

Remarks:

By definition, charmed quarks have a charm of +1, charmed antiquarks have a charm of -1, and all other elementary particles have a charm of 0.

Charm is conserved in all particle interactions except weak interactions.

charmed quark
charmed antiquark

Category: elementary particle

Definition: One of the six flavors of quarks.

The properties of a charmed quark are:

property	value
generation	2nd
bare mass	~1100 MeV/c²
effective mass	~1500 MeV/c²
electric charge	+2/3
spin	1/2
charm	+1

Related terms: charm

Symbol: c

SI units: not applicable

Remarks:

chemical
chemical compound
compound

Category: generic term

Definition: A substance that consists of molecules of a specific atomic composition.

Related terms: chemical element

Symbol: not applicable

SI units: not applicable

Remarks:

Every molecule of a chemical compound consists of atoms of specific chemical elements in a fixed ratio.

chemical bond

Category: phenomenon

Definition: A bond between atoms in molecules.

Related terms: covalent bond, ionic bond

Symbol: not applicable

SI units: not applicable

Remarks:

chemical element

Category: generic term

Definition: A substance that can not be broken down into simpler substances by chemical means.

Related terms: periodic table

Symbol: not applicable

SI units: not applicable

Remarks:

There are 92 naturally occurring chemical elements.

chemical property

Category: concept

Definition: Those properties of chemical compounds that come into play in chemical reactions.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

chemical reaction

Category: phenomenon

Definition: An interaction between molecules, atoms, ions, or radicals to form one or more new substances.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

chemistry

Category: branch of science

Definition: The study of the composition, structure, and properties of substances and the chemical reactions that they undergo.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

chiral state
chirality

Category: property

Definition: For any particle with spin 1/2, two chiral states can be defined: right-handed and left-handed.

In a right-handed chiral state the spin of a particle is oriented in generally the same direction as the linear momentum of the particle; for massless particles, exactly the same direction. In this case, the particle is said to have helicity +1.

In a left-handed chiral state the spin of a particle is oriented in generally the opposite direction as the linear momentum of the particle ; for massless particles, exactly the opposite direction. In this case the particle is said to have helicity -1.

Related terms:

Symbol: u_L (left-handed), u_R (right-handed)

SI units: not applicable

Remarks:

chronon

Category: hypothetical particle

Definition: A hypothetical particle of time; the time required for a photon to traverse the diameter of an electron.

Related terms: none

Symbol: ??

Values: 1 chronon » 10^-24 second

Remarks:

circuit
electric circuit

Category: concept

Definition: A continuous loop along which an electric current does or may flow.

For a list of other related terms see: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

circular motion

Category: phenomenon

Definition: Motion in which an object moves in a circular path.

Related terms: revolution, rotation

For a list of other related terms see: motion

Symbol: not applicable

SI units: not applicable

Remarks:

circular polarization

Category: concept

Definition: A wave pattern for electromagnetic waves in which the electric field vectors and magnetic field vectors rotate, with constant magnitude, in a plane perpendicular to the direction of propagation.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

classical dynamics

Category: branch of physics

Definition: The study of dynamics in which relativistic or quantum effects are not significant.

Related terms: none

Symbol: not applicable

SI units: not applicable

Category: concept

Definition: A surface that entirely encloses a volume of space.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

closed system

Category: concept

Definition: A system that can not exchange mass with the surroundings.

Related terms: open system, isolated system

Symbol: not applicable

SI units: not applicable

Remarks:

A closed system may exchange energy with the surroundings.

closed universe

Category: concept

Definition: A universe that is of finite spatial size.

Related terms: open universe

Symbol: not applicable

SI units: not applicable

Remarks:

A closed universe has no boundaries in spite of its finite size. An analogy, in reduced dimensionality, is the surface of a balloon.

According to general relativity, a closed universe will collapse after a finite lifetime and presumably end in a Big Crunch.

cluster of galaxies
galaxy cluster

Category: phenomenon

Definition: A group of galaxies that are close together and gravitationally related.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

coefficient

Category: common term

Definition:

A constant factor in a mathematical product. (eg. the a in ax)
A constant that is the ratio of one quantity to another quantity. The constant is usually conditional and the ratio is usually experimentally determined.

Related terms: none

Symbol: varies

SI units: varies

Remarks:

coefficient of friction
coefficient of sliding friction
coefficient of kinetic friction
coefficient of static friction

Category: scalar quantity

Definition: The ratio of the magnitude of the force opposing motion to the magnitude of the normal force between the surfaces involved.

Related terms: friction

Symbol: μ

SI units: newtons / meter²

Remarks:

The mathematical expression for the coefficient of friction is:

μ = F / N

where:

F = opposing force

N = normal force

Two cases are usually distinguished: static friction and sliding friction

coefficient of mutual inductance

Category: empirical constant

Definition: The ratio of the back emf induced in one electric circuit by a changing electric current in a second electric circuit to the rate of change of the electric current in the second electric circuit.

Related terms: mutual inductance

For a list of other related terms see: electric induction

Symbol: M

SI units: henrys = newton × meter × seconds² / coulomb²

Remarks:

The mathematical expression for a coefficient of mutual inductance is:

M = - E / (dI/dt)

where:

M = coefficient of mutual inductance

E = induced emf

I = electric current in the second electric circuit

t = time

coefficient of self-inductance

Category: empirical constant

Definition: The ratio of the back emf induced in an electric circuit by a changing electric current in the same electric circuit to the rate of change of the electric current in the electric circuit.

Related terms: self-inductance

For a list of other related terms see: electric induction

Symbol: L

SI units: henrys = newton × meter × seconds² / coulomb²

Remarks:

The mathematical expression for a coefficient of self-inductance is:

L = - E / (dI/dt)

where:

L = coefficient of self-inductance

E = induced emf

I = electric current in the electric circuit

t = time

coefficient of viscosity

Category: property

Definition: The ratio of the velocity gradient to the driving force in laminar flow.

Related terms: kinematic viscosity, Newtonian fluid, viscosity

Symbol: μ

SI units: newton seconds / meter²

Remarks:

cofactor of a matrix

Color is the charge that produces the strong force.

The term color as used here has nothing whatever to do with the ordinary meaning of color.

Each flavor of quark has one of three colors (usually called red, green, and blue).

By definition, quarks have plus colors; antiquarks have minus colors.

A particle that consists of three quarks of which one has red color, one has blue color, and one has green color is said to be colorless.

Likewise, a particle that consists of a quark that has plus red / green / blue color, and an antiquark that has minus red / green / blue color , is also said to be colorless.

All naturally occurring particles are colorless.

Color is a conserved quantity in strong interactions.

Color charges interact via the color gauge fields (or gluon field).

Color charges are analogous to electric charges (which interact via electromagnetic fields).

common term

In this glossary, certain terms are defined to be common terms. An effort has been made to use these words carefully and consistently. The following remarks may clarify how these terms are used.

One of the terms categorized as a common term is object.

The idea that an object is at rest is a concept.
The motion of an object is an example of a phenomenon.
The mass of an object is a property of the object.
A round object would have the quality of roundness.
The velocity of an object is a quantity.
An object is composed of substances.
Two or more objects form a system.
The proposition that an object is composed of atoms is a theory.

commutative
anticommutative

Category: property

Definition: The elements of a mathematical expression are commutative if they combine in such a manner that the result is independent of the order in which the elements are taken.

The elements of a mathematical expression are anticommutative if they combine in such a manner that the sign of the result is dependent on the order in which the elements are taken.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

These terms are applied to operators as well as operands.

Examples:

Commutative:

A + B = B + A

AB = BA

A • B = B • A

Anticommutative:

AB = -BA

Category: concept

Definition: A number that consists of two parts, one part of which is a real number and the other part of which is an imaginary number.

Related terms: number

Symbol: a + bi

SI units: not applicable

Remarks:

Complex numbers are the union of the real numbers and the imaginary numbers.

The usual notation is:

a + ib

where:

a = the real part

b = is the imaginary part

i =

Note that the plus sign does not indicate addition; it is merely a convention. The notation could also be (a,b) with the understanding that the first number is the real part and the second number the imaginary part.

component
vector component
component of a vector

Category: vector quantity

Definition: A component of a given vector is a vector equal to the projection of the given vector on a line in a specified direction.

Related terms: scalar component

Symbol: ??

SI units: varies

Remarks:

The mathematical expression for the component of a vector in the r direction is:

v_r = (v • r^) r^

where:

v_r = component of v in the direction of r

v = specified vector

r^ = unit vector in the direction of r

Category: phenomenon

Definition: The result of an interaction between a photon and an electrically charged particle in which some of the energy of the photon is transmitted to the particle and the wavelength of the photon is increased.

Related terms: scattering

Symbol: not applicable

SI units: not applicable

Remarks:

The increase in wavelength of the photon is given by the Compton equation:

Δλ = (2h/m₀c)sin²(φ/2)

where:

Δλ = the change in wavelength

h = the Planck constant

m₀ = the rest mass of the particle

c = the speed of light

φ = the angle between the directions of the incident photon and the scattered photon.

h/m₀c = the Compton wavelength (λ_C)

The Compton wavelength for an electron is 0.00243 nm.

Remarks:

Examples:

The expressions a + ib and a - ib are complex conjugates.

A positron is a conjugate of an electron.

Category: principle

Statement: If only conservative forces are acting, the total mechanical energy of an isolated system is constant.

Related terms: conserved

Symbol: not applicable

SI units: not applicable

Remarks:

conservation of momentum
conservation of momentum principle

Category: principle

Statement: In the absence of external forces, the linear momentum and the angular momentum of an isolated system are constant.

Related terms: conserved

Symbol: not applicable

SI units: not applicable

Remarks:

conservative field
conservative force

Category: field

Definition: A force field in which the work required to move a particle from one point to another is independent of the path taken.

Related terms: conservative

For a list of other related terms see: field, force

Symbol: not applicable

SI units: not applicable

Remarks:

conservative system

Category: concept

Definition: A system in which there is no loss (or gain) of mechanical energy.

Related terms: energy

Symbol: not applicable

SI units: not applicable

Remarks:

conserved

Category: concept

Definition: Unchanged by a specific physical process.

Symbol: not applicable

SI units: not applicable

Remarks:

For a list of quantities that are conserved, see conserved quantities.

Conserved may be compared with invariant, which means unchanged by a mathematical operation.

A particular quantity may be conserved under some physical processes but not others. In particular, some quantities are conserved in strong interactions but not in weak interactions.

conserved quantity

Category: concept

Definition: A quantity that is conserved in a physical process.

Related terms: conserved

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

Quantities that may be conserved include:

angular momentum
baryon number
beauty
charge conjugation parity
charm
color
electric charge
energy
G-parity
hypercharge
isospin
lepton number
linear momentum
mechanical energy
parity
parity
spin
strangeness
third component of isotopic spin
time
truth
unitary spin

constant

Category: generic term

Definition:

A number or quantity that has a fixed value in a given situation or universally or that is a characteristic of some substance.
Unchanged during an experiment, a given process, or a specified time interval.

Symbol: varies

SI units: varies

Remarks:

constant of the motion

Category: concept

Definition: (to be completed at a later time

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

constraint

Category: concept

Definition: A restriction on the natural degrees of freedom of a system.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

If the motion of a system is subject to frictionless constraining forces, then the forces between the system and the constraint are equal and opposite and do no net work.

contact force

Category: vector quantity

Definition: The force that an object exerts on another object with which it is in contact.

Related terms: normal force

Symbol: F

SI units: newtons

Remarks:

continuity principle
continuity equation
equation of continuity

Category: principle

Statement: During a time interval, the change in the amount of a quantity within a closed surface is equal to the net flow of the quantity through the surface provided that there are no sources or sinks of the quantity within the closed surface.

Related terms: divergence theorem, Gauss's law

Symbol: not applicable

SI units: not applicable

Remarks:

A common way of stating the continuity principle is to say: input equals output plus accumulation.

The mathematical expression of the continuity principle is:

Ñ • v = -¶ρ / ¶t

where:

v = flux of a quantity at a point

ρ = density of the quantity at the point

t = time

Examples:

In electrodynamics:

Ñ • J = -¶ρ / ¶t

where:

J = volume current density of electric charge

ρ = electric charge density

In fluid dynamics:

Ñ • ρv = -¶ρ / ¶t

where:

ρ = mass density

v = velocity

continuous
noncontinuous

Category: quality

Definition:

Having uninterrupted extension in space, time, or sequence.
Having the characteristic that the numerical difference between the value at a point and the value at any other point in a sufficiently small neighborhood of the point is arbitrarily small.

Related terms: discrete

Symbol: not applicable

SI units: not applicable

Remarks:

continuous function

Category: concept

Definition: A mathematical function that has no abrupt changes in value.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

A sine function is a continuous function, a tangent function is not.

continuum

Category: concept

Definition: Something absolutely continuous and homogeneous of which no distinction of content can be affirmed except by reference to something else as duration or extension.

Related terms: space, space-time

Symbol: not applicable

SI units: not applicable

Remarks:

contravariant

Category: notational convention

Definition: (`to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

contravariant vector

Category: notational convention

Definition: A space-time 4-vector with the sign of the temporal coordinate set negative.

a^μ = (-a⁰, a¹, a², a³)

where:

a⁰ is the temporal coordinate

a¹, a², a³ are the spatial coordinates

Symbol: a^μ

SI units: not applicable

Remarks:

It is important to note that the index variable of a contravariant vector is a superscript.

Covariant vector: a_μ = (+a₀, a₁, a₂, a₃)

Contravariant vector: a^μ = (-a⁰, a¹, a², a³)

convection

Category: phenomenon

Definition: The transmission of energy in a fluid by the movement of the fluid itself.

Related terms: forced convection, natural convection

Symbol: not applicable

SI units: not applicable

Remarks:

coordinate

Category: concept

Definition: One of the numbers that define the position of a point relative to a reference frame.

Related terms: coordinate systems

Symbol: not applicable

SI units: not applicable

Remarks:

coordinate system

Category: concept

Definition: A scheme for locating points in a given reference frame by means of a set of numbers. Each of these numbers is called a coordinate of a point.

Symbol: not applicable

SI units: not applicable

Remarks:

The three most-used coordinate systems for a three-dimensional Euclidean space are : the Cartesian coordinate system, the cylindrical polar coordinate system, and the spherical polar coordinate system

In an n-dimensional space, n numbers are required to specify the position of a point.

coordinate transformation

Category: mathematical operation

Definition: A mathematical transformation of coordinates.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

Space inversion

Conversion from Cartesian coordinates to spherical polar coordinates.

coordinated clocks

Category: concept

Definition: If two clocks are at rest in an inertial reference frame and each appears to indicate the same time when observed by an observer at rest in the reference frame and at a point midway between the clocks, the clocks are said to be coordinated clocks.

Related terms: relativity

Symbol: not applicable

SI units: not applicable

Remarks:

Copenhagen interpretation

Category: hypothesis

Definition: One of the philosophical views of the events described by quantum mechanics.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The use of the name "Copenhagen" stems from the fact that one of the principal architects of quantum mechanics was Niels Bohr who came from Copenhagen. Bohr was a strong advocate of the Copenhagen convention and defended it vigorously in debates with Albert Einstein.

Coriolis acceleration

Category: pseudovector quantity

Definition: A pseudoacceleration corresponding to the Coriolis force.

Related terms: Coriolis theorem

Symbol: ??

SI units: meters / second²

Remarks:

Coriolis force

Category: pseudovector quantity

Definition: A pseudoforce that allows an observer in a rotating reference frame to describe the motion of a object in terms of Newton's laws of motion.

Related terms: Coriolis acceleration, Coriolis theorem

Symbol: ??

SI units: newtons

Remarks:

Newton's laws of motion apply only in inertial reference frames, not in accelerating reference frames or rotating reference frames.

The Coriolis force acts at right angles to the path of the object in motion.

The Coriolis force comes into play only if the motion of the object has a radial component.

The mathematical expression for the Coriolis force is:

F = -2m(ω ´ v)

where:

F = Coriolis force

m = mass of the object

ω = angular velocity of the rotating reference frame

v = velocity of the object relative to the axis of the rotating reference frame

Coriolis theorem

Category: theorem

Statement: Given:

an inertial reference frame I
a rotating reference frame R
a object that is moving relative to R

The acceleration of the object relative to I is the vector sum of:

the acceleration of the object relative to R
the acceleration of R relative to I, and
the Coriolis acceleration, which is equal to twice the cross product of the angular velocity of R and the rectilinear velocity of the object relative to R

Related terms: Coriolis force

Symbol: not applicable

SI units: not applicable

Remarks:

correspondence principle

Category: principle

Statement: The mathematical expressions of quantum mechanics, when applied to macroscopic systems, must give the same results as classical mechanics.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

This principle was enunciated by Niels Bohr.

cosine
cosine function

Category: mathematical function

Definition: One of the trigonometric functions. The ratio of the adjacent side to the hypotenuse of a right triangle.

Related terms:

For a list of other related terms see: periodic functions

Symbol: cos

SI units: dimensionless

Related terms: trigonometric functions

Symbol: cos

SI units: dimensionless

Remarks:

cosmic

Category: ??

Definition: Of, or relating to the universe.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

cosmic microwave background radiation

Category: phenomenon

Definition: Diffuse electromagnetic radiation from outer space.

Related terms: Big Bang

Symbol: not applicable

SI units: not applicable

Remarks:

Cosmic background radiation is thought to have originated approximately 300,000 years after the Big Bang when electromagnetic radiation and matter became decoupled.

The observance of cosmic microwave background radiation is thought to be strong evidence of the Big Bang.

The intensity of cosmic microwave background radiation is very nearly equal from all directions.

cosmic rays

Category: phenomenon

Definition: The unit of measurement of electric charge in the SI system of units.

Related terms: none

Symbol: C

SI units: 1 coulomb = 1 ampere × second

Remarks:

A coulomb is the electric charge transmitted in one second by an electric current of one ampere.

coulomb force

Category: vector quantity

Definition: The force that the electric field produced by a source charge at rest in the lab frame exerts on a test electric charge.

Related terms: electric field strength

For a list of other related terms see: force, field

Symbol: varies

SI units: newtons

Remarks:

The magnitude of the force is given by Coulomb's law.

Coulomb's law

Category: law

Statement: The force (F) that a source charge (q) in a vacuum and at rest in the lab frame exerts on a test electric charge (Q) is proportional to the product of the magnitude of the two electric charges and inversely proportional to the square of the distance (r) between the two charges.

Related terms: inverse square law

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of Coulomb's law is:

F = (1 / ε₀)(1 / 4πr²)(Qq)r^

where:

Category: concept

Definition: A violation of CP invariance.

Changed under simultaneous charge conjugation and space inversion.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

CPT invariance

Category: concept

Definition: Invariance under simultaneous charge conjugation, space inversion, and time reversal.

Related terms: none

Symbol: CPT

SI units: not applicable

Remarks:

CPT theorem

Category: theorem

Statement: Simultaneous charge conjugation, space inversion, and time reversal is a fundamental symmetry in relativistic quantum field theory.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

In other words, there is no known instance in which a quantity (or property) changes under simultaneous charge conjugation, space inversion, and time reversal.

critical

Category: concept

Definition: A state in which or a point at which a property, quality, quantity, or phenomonen suffers an major change.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

critical angle
critical mass
critical pressure
critical temperature

critical angle

Category: phenomenon

Definition: The angle of incidence of light, proceeding from a denser medium to a less dense one, at which grazing refraction occurs.

Related terms: none

Symbol: ??

SI units: radians

Remarks:

Light incident at a greater angle suffers total internal reflection.

critical damping

Category: phenomenon

Definition: Damping such that the damped oscillator fails to oscillate.

Related terms: damping

Symbol: not applicable

SI units: not applicable

Remarks:

critical density

Category: concept

Definition: The density of the universe that would be midway between an open universe and a closed universe.

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

critical mass

Category: concept

Definition: The minimum mass of a fissile substance that will sustain a chain reaction.

Related terms: none

Symbol: ??

SI units: kilograms

Remarks:

critical point

Category: concept

Definition: The intersect of the critical temperature and critical pressure.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

At the critical point, the properties of the vapor and liquid states of a substance are equal.

critical pressure

Category: scalar quantity

Definition: The vapor pressure of a substance at its critical temperature.

Related terms: none

Symbol: ??

SI units: pascals = newtons / meter²

Remarks:

critical temperature

Category: scalar quantity

Definition: The temperature above which a given substance cannot be liquefied.

Related terms: critical pressure

Symbol: ??

SI units: kelvin

Remarks:

cross product
vector product

Definition: A pseudovector the magnitude of which is equal to the product of the magnitudes of the two vectors multiplied by the sine of the least angle between them.

The direction of the cross product is perpendicular to the plane containing the two vectors and positive in the direction determined by the right-hand rule with the direction of rotation from the first stated vector to the second.

Related terms: dot product, pseudovector

Symbol: A ´ B

SI units: not applicable

Remarks:

The mathematical expression for the magnitude of a cross product is:

|A ´ B| = |A||B|sin θ

where:

A, B = two vectors

|A| = magnitude of vector A

|B| = magnitude of vector B

θ = least angle between A and B

A cross product does not commute:

B ´ A = - (A ´ B)

cross section

Category: scalar quantity

Definition: A measure of the probability of a particular collision process, stated as the effective area particles present to incident particles for that physical process.

Related terms: none

Symbol: σ

SI units: meters²

Remarks:

curie

Definition: A unit of measurement of ionizing radiation.

Related terms: none

Symbol: Ci

Values: 1 Ci = 3.7 × 10¹⁰ Becquerels

Remarks:

Becquerel is preferred over curie.

curl

Category: mathematical operation

Definition: The cross product of the del operator and a vector function

Related terms:

For a list of other related terms see: del operator

Symbol: see remarks

SI units: not applicable

Remarks:

The mathematical expression for a curl is:

curl v = Ñ ´ v

where:

v is a vector quantity.

Ñ is the del operator

current

Category: vector quantity

Definition: The rate of flow of a quantity.

Related terms: electric current

Symbol: varies

SI units: varies

Remarks:

The term current is often used when electric current is the intended meaning.

current density
electric current density

Category: vector quantity

Definition: The amount of electric current per unit of extent.

For a list of other related terms see: electricity and magnetism

Symbol: J (surface current density), K (volume current density)

SI units: varies

Remarks:

curvature

Category: concept

Definition: The reciprocal of the radius of curvature.

Related terms: none

Symbol: ??

SI units: meters^-1

Remarks:

cycle

Category: concept

Definition: One complete repetition of a periodic process.

Related terms: period, periodic motion, wavelength

Symbol: not applicable

SI units: not applicable

Remarks:

cylindrical polar coordinates
cylindrical polar coordinate system

Category: concept

Definition: A coordinate system based on:

an origin
a plane through the origin
a base line in the plane through the origin
an axis perpendicular to the plane through the origin

Related terms:

For a list of other related terms see: coordinate systems

Symbol: not applicable

SI units: not applicable

Remarks:

The coordinates of a point, using the most common symbols, are:

r	distance from the origin to the projection of the point on the plane
θ	the right-handed angle between the base line and a plane though the axis and the point
z	the distance from the origin to the projection of the point on the axis

damping force

Category: vector quantity

Definition: A force that causes damping.

Related terms: damping

Symbol: F

SI units: newtons

Remarks:

dark matter

Category: concept

Definition: Matter that is undetectable except for its gravitational effects.

Related terms:

For a list of other related terms see: particle categories

Symbol: not applicable

SI units: not applicable

Remarks:

As of June 2001, the existence of dark matter has not been proven.

de Broglie equation

Category: ??

Definition: An equation relating the wavelength of the wave-like behavior of a particle to the mass and velocity of the particle:

λ = h / mv

where:

λ = wavelength

m = rest mass of the particle

v = velocity of the particle

Related terms: de Broglie waves

Symbol: not applicable

SI units: not applicable

Remarks:

de Broglie wave
matter wave
phase wave

Category: mathematical function

Definition: A set of wave functions that represent the wave-like behavior of a particle.

Symbol: not applicable

SI units: not applicable

Remarks:

De Broglie waves are sometimes regarded as waves of probability since the square of the amplitude of the de Broglie wave at a given point represents the probability of finding the particle in a unit volume at that point.

de Broglie's hypothesis

Category: hypothesis

Statement: Material particles, such as an electron, have a wave nature a well as a particle nature.

Related terms: wave-particle duality

Symbol: not applicable

SI units: not applicable

Remarks:

decay
disintegration

Category: process

Definition: A physical process in which a nucleus emits one or more particles either spontaneously or as a result of a collision with another particle.

Symbol: not applicable

SI units: not applicable

Remarks:

In decay, a parent nucleus is changed to a daughter nucleus and one or more of the following are emitted:

alpha particle	nucleus of helium 4
beta particle	electron or positron
gamma ray	photon
neutral particle	neutrino or antineutrino

decay constant

Category: scalar quantity

Definition: The probability of decay of a particle in 1 second.

Related terms: decay

Symbol: λ

SI units: seconds^-1

Remarks:

Definition: One 360th of a circle.

Related terms: angle

Symbol: º

SI units: radians

Remarks:

360º = 2 π radians.

degrees of freedom

Category: concept

Definition: The number of independent variables needed to describe the state of a system.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

del operator
del
nabla

Category: operator

Definition: The three-dimensional differential operator.

Related terms: cross product, curl, derivative, divergence, dot product, gradient, vector

Symbol: Ñ

SI units: not applicable

Remarks:

In Cartesian coordinates:

Ñ = i^(¶/¶x) + j^(¶/¶y) + k^(¶/¶z)

where:

i^, j^, k^ are the unit vectors for the x,y,z axes

density
mass density

Category: scalar quantity

Definition: The amount of a quantity per unit of volume.

Related terms: number density

Symbol: ρ

SI units: kilograms / meter³

Remarks:

Unless the quantity is specified or clear from the context, the quantity implied is mass.

dependent variable

Category: concept

Definition: A mathematical variable whose value is dependent upon one or more independent variables.

Related terms: none

Symbol: varies

SI units: not applicable

Remarks:

derivative

Definition: The limit of the ratio of the change in a mathematical function to the corresponding change in an independent variable as the change in the independent variable approaches zero.

Related terms: del operator, differentiation

Symbol: ??

SI units: not applicable

Remarks:

The mathematical expression of a derivative is:

derived quantity

Category: generic term

Definition: A quantity that is defined in terms of base quantities.

Related terms: units of measurement,

Symbol: not applicable

SI units: not applicable

Remarks:

derived unit
derived unit of measurement

Category: generic term

Definition: A unit of measurement formed by an algebraic combinations of base units of measurement.

Related terms: units of measurement

Symbol: not applicable

SI units: not applicable

Remarks:

The units of measurement of some derived quantities have been given special names. When a special name has not been given, the units of measurement are expressed in combinations of base units and/or other derived units.

Examples:

Derived units that have been assigned special names

derived quantity	special name	equivalent in base units
electric charge	coulomb	ampere × second
energy	joule	kilogram × meter² / second²
force	newton	kilogram × meter / second²
electric capacitance	farad	coulombs² / newton × meter
electric resistance	ohm	newton × meter × seconds / coulomb²
electric conductance	siemens	coulomb² / newton × meter × second
magnetic flux density	tesla	newton × seconds / coulomb × meter
electric potential	volt	newton × meters
magnetic flux	weber	newton × seconds / coulomb × meter
power	watt	newton × meters / second

Derived units expressed in terms of base units.

derived quantity	base units
area	meter²
speed	meter / second
volume	meter³

determinant

Definition: The value obtained by a series of mathematical operations on a square array of numbers. See a mathematical reference for a description of the mathematical operations.

Related terms: matrix

Symbol: not applicable

SI units: not applicable

Remarks:

The term determinant is also applied to the array itself.

deterministic
determinism
causality
causality principle
causation

Category: concept

Definition: The idea that every event is determined by an antecedent cause or causes.

Related terms: probabilistic

Symbol: not applicable

SI units: not applicable

Remarks:

deuterium

Category: chemical element

Definition: The isotope of hydrogen that has one neutron in the nucleus.

Related terms: tritium

Symbol: D

SI units: not applicable

Remarks:

dielectric
dielectric medium

Category: substance

Definition: A nonconductor of direct electric current.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

differential

Definition:

An arbitrarily small increment in an independent variable.
The product of the derivative of a mathematical function of one variable by the differential increment of the independent variable.

Related terms: differentiation

Symbol: d

SI units: not applicable

Remarks:

Examples:

dx
dy = (dy/dx)dx

differential equation

Category: mathematical expression

Definition: An equation containing differentials or derivatives of mathematical functions.

Related terms: differentiation

Symbol: not applicable

SI units: not applicable

Remarks:

differential operator

Category: operator

Definition: A mathematical operator that indicates differentiation.

Related terms: differentiation

Symbol: d, ¶

SI units: not applicable

Remarks:

differentiation

Category: mathematical operation

Definition: The process of obtaining a derivative.

Symbol: not applicable

SI units: not applicable

Remarks:

diffraction

Category: phenomenon

Definition: The tendency of waves to bend around an obstacle that they pass near.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

diffusion

Category: phenomenon

Definition:

In electricity and magnetism, the scattering of electromagnetic radiation upon reflection or transmission.
In fluid mechanics, the phenomenon in which a substance is transmitted into and through another substance under the influence of a driving force.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

diffusivity

Category: scalar quantity

Definition: A measure of the rate at which heat is transmitted through a substance. It is equal to the thermal conductivity divided by the specific heat at constant pressure and the density.

Related terms: none

Symbol: α

SI units: meters² / second

Remarks:

The mathematical expression for diffusivity is:

α = λ / ρc_p

where:

α = diffusivity

λ = thermal conductivity

ρ = density

c_p = specific heat at constant pressure

dimension

Category: concept

Definition:

A spatial or temporal extension.
A coordinate specifying a position in space and/or time.
The type of a unit of measurement used in specifying the amount of a quantity or property.

Related terms: extent

Symbol: not applicable

SI units: varies

Remarks:

dimensional analysis

Category: ??

Definition: An examination of the units of measurement involved in an mathematical expression that describes a phenomenon.

Related terms: dimension

Symbol: not applicable

SI units: not applicable

Remarks:

dimensionless
dimensionless number

Category: number

Definition: Having no applicable units of measurement.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

By definition, a quantity or property can not be dimensionless.

Usually, a dimensionless number is the result of a combination or ratio of several quantities in which all the dimensions cancel out.

Examples:

absorptance
cosine
electric susceptibility
emissivity
fine structure constant
Froude number
index of refraction
Lorentz factor
Mach number
magnetic susceptibility
reflectance
relative permeability
relative permittivity
Reynolds number
sine
specific gravity

dipole

Category: phenomenon

Definition:

electric dipole
magnetic dipole

Related terms: dipole moment

Symbol: not applicable

SI units: not applicable

Remarks:

dipole moment

Category: vector quantity

Definition:

electric dipole moment
magnetic dipole moment

Related terms: dipole

Symbol: m

SI units: not applicable

Remarks:

Dirac delta function

Category: mathematical expression

Definition: A mathematical function, of a single variable, that has a value of 1 at a specific value of the variable and 0 for every other value of the variable.

Related terms: none

Symbol: δ(x)

SI units: not applicable

Remarks:

Dirac equation

Category: mathematical expression

Definition: An equation for the wave functions of fermions.

Related terms: Schrodinger wave equation

Symbol: not applicable

SI units: not applicable

Remarks:

The Dirac equation may be regarded as a version of the Schrodinger wave equation that takes relativity into account.

direct current
direct electric current

Category: scalar quantity

Definition: An electric current that moves in one direction only.

Category: vector quantity

Definition:

A vector representing in direction and magnitude the difference in position between a given point and an original, standard, or other reference point.

For other uses of the term "displacement" see electric displacement and fluid displacement.

Related terms: position vector

Symbol: r

SI units: not applicable

Remarks:

The displacement vector between two points is given by:

r = (x₂-x₁)i^ + (y₂-y₁)j^ + (z₂-z₁)k^

where:

(x₁,y₁,z₁) are the coordinates of point 1

(x₂,y₂,z₂) are the coordinates of point 2

i^, j^, k^ are the unit vectors for the x,y,z axes

dissociation energy

Category: scalar quantity

Definition: The energy required to break a chemical bond.

Related terms: none

Symbol: ??

SI units: joules = newton × meters

Remarks:

distance

Category: scalar quantity

Definition:

The amount of separation between two points, lines, surfaces, or objects measured along the shortest path joining them.
The length of a path.

Related terms: length

Symbol: s

SI units: meters

Remarks:

distribution

Category: phenomenon

Definition: The fraction, number, or amount of a quantity as a function of position over an extent or interval.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

distribution function

Category: mathematical expression

Definition: The mathematical expression of a frequency distribution.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

divergence

Definition: The dot product of the del operator and a vector function.

Related terms:

For a list of other related terms see: del operator

Symbol: see remarks

SI units: not applicable

Remarks:

Divergence can be interpreted as the net flow per unit of volume of the vector quantity out of an element of volume in a vector field. A divergence is zero unless the element of volume contains a source or a sink.

The mathematical expression for divergence is:

div v = Ñ • v

where:

v is a vector quantity.

Ñ is the del operator

In Cartesian coordinates:

where:

v_x = scalar component of v in x direction

v_y = scalar component of v in y direction

v_z = scalar component of v in z direction

divergence theorem
Gauss's theorem
Green's theorem

Category: theorem

Statement: The integral of the divergence of a vector function over a volume is equal to the integral of the vector function over the surface enclosing the volume.

Related terms: continuity principle, Gauss's law

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression for the divergence theorem is:

where:

v = vector function

dτ = element of volume

n = unit vector normal to the surface

dσ = element of surface

domain

Category: concept

Definition:

A region of space thoughout which an influence is exerted.
A set to which a condition applies.
In mathematics, the set of elements to which a mathematical or logical variable is limited.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Doppler effect

Category: phenomenon

Definition: The change in apparent frequency or wavelength of waves such as light or sound as a result of the relative motion of the source and the observer.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

For electromagnetic radiation:

where:

λ = wavelength as measured in the lab frame

λ₀ = wavelength as measured in the moving frame

v = velocity of the source as measured in the lab frame

Doppler shift

Category: scalar quantity

Definition: The magnitude of the change in frequency or wavelength of waves that results from the Doppler effect.

Related terms: none

Symbol: not applicable

SI units: hertz

Remarks:

dot product
scalar product

Definition: The product of the magnitude of two vectors multiplied by the cosine of the angle between them.

Related terms: cross product

Symbol: A • B

SI units: not applicable

Remarks:

A dot product is a scalar.

The dot product can be interpreted as the magnitude of one vector multiplied by the magnitude of the component of the other vector in the direction of the first vector.

The mathematical expression for a dot product is:

A • B = |A||B|cos θ

where:

A, B = two vectors

|A| = magnitude of vector A

|B| = magnitude of vector B

θ = angle between A and B

down quark
down antiquark

Category: elementary particle

Definition: One of the six flavors of quarks.

The properties of a down quark are:

property	value
generation	1st
bare mass	~7.5 MeV/c²
effective mass	~350 MeV/c²
electric charge	-1/3
spin	1/2
downness	+1

Related terms: downness, quarks

Symbol: d

SI units: not applicable

Remarks:

downness

Category: quantized property

Definition: Downness is a quantized property and an additive quantum number associated with quarks.

Related terms: quantum number

Symbol: d

Values: -1, 0, or +1

Remarks:

By definition, down quarks have a downness of +1, down antiquarks have a downness of -1, and all other elementary particles have a downness of 0.

Downness is conserved in all particle interactions except weak interactions.

driving force

Category: vector quantity

Definition: A force that is causing a motion.

Related terms: none

Symbol: F

SI units: newtons

Remarks:

duration

Category: scalar quantity

Definition: The time interval over which a condition exists or a process occurs.

Related terms: none

Symbol: Δt

SI units: seconds

Remarks:

dynamic

Category: concept

Definition:

Of, or related to force or energy.
Of, or related to dynamics.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

dynamic similarity
similarity principle

Category: concept

Definition: The condition that two or more systems exhibit geometrically similar motions.

Related terms: similarity principle

Symbol: not applicable

SI units: not applicable

Remarks:

In the motion of fluids, dynamic similarity may be attained when certain dimensionless numbers are equal. In this case, the dimensionless numbers may include: Reynolds number, Froude number, Mach number, etc.

dynamic system

Category: concept

Definition: A system in which at least some of the parts are in motion.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Category: notational convention

Definition: Summation is implied whenever a Greek index is repeated in a product, once as a covariant index and once as a contravariant index.

a_μb^μ = -a⁰b⁰ + a¹b¹ + a²b² + a³b³

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Einstein's law

Category: law

Statement: Energy and mass are related according to the following equation:

E = mc²

where:

E = energy

m = mass

Mathematical expressions:

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Einstein's theory of relativity

Category: theory

Definition: Actually two theories:

the special theory of relativity, which deals with inertial reference frames
the general theory of relativity, which deals with accelerated reference frames.

Related terms: relativity

Symbol: not applicable

SI units: not applicable

Remarks:

elastic
elasticity
inelastic

Category: property

Definition: The property of a object or substance by which it tends to resume is original size and shape after being subjected to deforming stresses.

Related terms: elastic hysteresis

For a list of other related terms see: stress

Symbol: not applicable

SI units: not applicable

Remarks:

elastic collision

Category: phenomenon

Definition:

In mechanics, a collision in which the total kinetic energy of translation is unchanged after the collision.
In nuclear physics, a collision in which the incoming particle is scattered without exciting or breaking up the struck nucleus.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

elastic hysteresis

Category: phenomenon

Definition: When stress is gradually applied to an elastic object and then gradually removed, it is observed that, at the same stress, the strain when unloading is greater than the strain when loading. This phenomenon is called elastic hysteresis.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The difference in the strain when unloading and the strain when loading is dependent on:

the nature of the substance
the history of the substance
the rate of application and removal of stress

elastic limit

Category: phenomenon

Definition: The smallest stress that leaves a detectable permanent strain after removal of the stress.

Related terms: none

Symbol: ??

SI units: newtons / meter²

Remarks:

elastic scattering

Category: concept

Definition: Scattering in which there is no net change in the internal energy of the particles involved.

Related terms: scattering

Symbol: not applicable

SI units: not applicable

Remarks:

electric

Category: property

Definition: Of, or relating to electricity.

Related terms: magnetic

For a list of other related terms see: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

electric admittance

Category: scalar quantity

Definition: Electric admittance is the reciprocal of electric impedance.

Related terms: none

For a list of other related terms see: electric impedance

Symbol: Y

SI units: siemens = ampere / volt = coulomb² / newton × meter × second

Remarks:

Electric admittance is related to electric conductance (G) and electric susceptance (B) by the following mathematical expression

Y² = G² + B²

electric capacitance
capacitance

Category: scalar quantity

Definition:

When an electric potential is applied to an isolated conductor, the ratio of the electric charge that accumulates on the conductor to the electric potential.
When an electric potential is applied between two conductors, the ratio of the electric charge that accumulates on one of the conductors to the electric potential.

Related terms: none

For a list of other related terms see: electric impedance

Symbol: C

SI units: farad = coulombs / volt = coulombs² / newton × meter

Remarks:

The mathematical expression for the electric capacitance is:

C = Q / V

where:

C = electric capacitance

Q = electric charge

V = electric potential difference

electric charge
negative electric charge
positive electric charge

Category: quantized property

Definition: Electric charge is a quantized property and additive quantum number associated with charged leptons and quarks.

Related terms: charge

For a list of other related terms see: electricity and magnetism, interaction

Symbol: Q, q

SI units:1 coulomb = 1 ampere × second

Remarks:

Electric charge is the charge that produces the electromagnetic force.

There are two equal and opposite forms of electric charge. These have been assigned the terms positive electric charge and negative electric charge.

By convention, the electric charge of an electron is considered to be negative in sign.

The electric charge of a proton is thought to be exactly equal to the electric charge of an electron except that it is opposite in sign (positive).

The electric charge of an antiparticle is opposite in sign to the electric charge of its corresponding normal particle.

The electric charge of an electron is thought to be the smallest electric charge that can have separate existence.

Quarks are thought to have electric charges of ±1/3 or ±2/3, but do exist outside of nuclei.

The elementary particles that have electric charge are: electron, muon, tauon, quarks, and their antiparticles. Neutrinos do not have an electric charge.

electric charge density
charge density

Category: scalar quantity

Definition: The number of unit electric charges per unit of extent.

The extent may be a line, a surface, or a volume.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: ρ (volume), σ (surface), λ (line)

SI units: coulombs / meter³ , coulombs / meter² , coulombs / meter

Remarks:

electric conductance
conductance

Category: scalar quantity

Definition:

In a direct current circuit, the reciprocal of the electric resistance
In an alternating current circuit, the real part of the electric admittance

Related terms:

For a list of other related terms see: electric impedance

Symbol: G

SI units: siemens = amperes / volt = coulomb² / newton × meter × second

Remarks:

electric conductivity

Category: scalar quantity

Definition:

A property of a medium that is equal to the ratio of the electric current divided by the electric potential gradient.
The volume current density (J) of an electric current divided by the electric field strength.

Related terms: resistivity

For a list of other related terms see: electricity and magnetism

Symbol: σ

SI units: siemens / meter = amperes / volt × meter = coulomb² / newton × meter² × second

Remarks:

The mathematical expression for electric conductivity is:

σ = J / E

Electric conductivity is the reciprocal of electric resistivity.

electric current

Category: base quantity

Definition:

A flow of electric charge.
The rate of flow of electric charge.

For a list of other related terms see: base quantities, electricity and magnetism

Symbol: I

SI units: amperes = coulombs / second

Remarks:

Electric current is a base quantity in the SI system of units.

By definition, the direction of motion of an electric current is the same as the direction of motion of the electric charges if the electric charges are positive electric charges and opposite in direction if the electric charges are negative electric charges.

Usually, an electric current is a flow of electrons. By definition, the electric charge of electrons is negative. Therefore, in this case, the direction of motion of the electric current is opposite to the direction of motion of the electrons. This unfortunate circumstance is due to an arbitrary choice made by Benjamin Franklin.

electric dipole

Category: concept

Definition: A system of two equal and opposite electric charges separated by a distance.

Related terms: magnetic dipole

For a list of other related terms see: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

electric dipole moment

Category: scalar quantity

Definition: The product of either of the electric charges in an electric dipole and the distance between the electric charges.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: p

SI units: coulomb × meters

Remarks:

electric energy

Category: scalar quantity

Definition:

The potential energy of a charged particle in an electric field.
The potential energy of a capacitor arising from the distribution of electric charges within it.
The energy per unit of volume of an electric field.
The energy of an electric current stored in a magnetic field.

Related terms:

For a list of other related terms see: electric field

Symbol: E

SI units: joules = newton × meters

Remarks:

E = QV

where:

Q = the electric charge on the particle

V = the electric potential at the point where the charge is located

E = 1/2 CV²

where:

C = the electric capacitance of a capacitor

V = the potential difference between the plates of the capacitor

E = εE_f²

where:

ε = permittivity of the electric field

E_f = electric field strength

E = 1/2 LI²

where:

L = self-inductance of a circuit

I = the current in the circuit

The electric potential per unit volume of an electric field is:

energy = (1/2)εE²

where:

ε = permittivity of the dielectric medium

E = magnitude of the electric field strength

electric field
E field

Category: phenomenon

Definition: A force field produced by an electric charge or by a changing magnetic field.

For a list of other related terms see: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

The terms electric field and E field are often used when electric field strength is the intended meaning.

An electric charge in motion also produces a magnetic field.

Notice that motion is dependent upon the choice of reference frame. Thus if an electric charge is at rest in the lab frame, an observer in the lab frame observes an electric field but not a magnetic field. On the other hand, an observer in a moving frame would observe both an electric field and a magnetic field.

In other words, electric fields and magnetic fields are simply different aspects of a single phenomenon: electromagnetic fields.

electric field flux

Category: scalar quantity

Definition: The flux of electric field strength through a surface.

Related terms:

For a list of other related terms see: electric field

Symbol: ??

SI units: volts / meter² = newtons / coulomb × meter

Remarks:

By Gauss's law, the total flux of electric field strength through a closed surface is equal to the total electric charge enclosed within the surface.

electric field strength (E)
electric intensity
electric field intensity
electric potential gradient

Category: vector quantity

Definition: The force that an electric field exerts on a test electric charge per unit of test electric charge. The direction of the force is in the direction of the field.

Related terms:

For a list of other related terms see: electric field

Symbol: E

SI units: volts / meter = newtons / coulomb

Remarks:

The mathematical expression for electric field strength is:

E = F / Q

where:

F = the force on the test electric charge

Q = magnitude of the test electric charge

According to Coulomb's law, the electric field strength of the electric field produced by a source electric charge in a vacuum and at rest in the lab frame is:

E = F / Q = (1 / ε₀)(1 / 4πr²)(q) r^

where:

r = distance from q to Q

q = magnitude of the source electric charge

r^ = unit vector in direction from q to Q

By Gauss's law, the total flux of electric field strength through a closed surface is equal to the total electric charge enclosed within the surface.

electric field vector

Category: vector quantity

Definition: The field quantity that defines an electric field.

Related terms:

For a list of other related terms see: electric field

Symbol: not applicable

SI units: ??

Remarks:

electric flux (Y)

Category: scalar quantity

Definition: The amount of electric charge displaced across an area in a dielectric medium by an electric field.

Related terms:

For a list of other related terms see: electric field

Symbol: ψ

SI units: coulombs

Remarks:

The mathematical expression for electric flux is:

ψ = D • a

= εE • a

where:

ψ = electric flux

D = electric flux density

a = area

ε = permittivity of the dielectric medium

electric flux density (D)
D field
electric displacement

Category: vector quantity

Definition: The amount of electric charge displaced across a unit area in a dielectric medium by an electric field.

Related terms: electric flux

For a list of other related terms see: electric field

Symbol: D

SI units: coulombs / meter²

Remarks:

The mathematical expression for electric flux density is:

D = εE

where:

D = electric flux density

ε = permittivity of the dielectric medium

The electric flux density at a point in an electric field in free space is ε₀E.

electric force

Category: vector quantity

Definition: The force that an electric field exerts on a electric charge at rest with respect to the source of the field.

Related terms: coulomb force

For a list of other related terms see: electric field

Symbol: varies

SI units: newtons

Remarks:

electric force law

Category: law

Statement: The force on an electric charge at rest in an electric field is proportional to the electric field strength and to the magnitude of the electric charge.

Related terms: electric force

For a list of other related terms see: electric field

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression for electric force is:

F = QE

where:

F = electric force

Q = electric charge

electric impedance

Category: scalar quantity

Definition: The ratio of rms electric potential difference to rms electric current when an alternating emf is applied to an electric circuit.

For a list of other related terms see: electricity and magnetism

Symbol: Z

SI units: ohms = newton × meter × seconds / coulomb²

Remarks:

Electric impedance is similar in meaning to electric resistance.

The mathematical expression for the electric impedance of an alternating current circuit is:

Z = V_rms / I_rms

where:

Z = electric impedance

V_rms = rms voltage

I_rms = rms electric current

Electric impedance is a function of electric resistance and electric reactance.

Z = (R² + X²)^½

Category: scalar quantity

Definition: The work required to move a unit positive electric charge from a point of zero electric potential to a specified point in an electric field.

The point of zero electric potential may be at an infinite distance from the source of the electric field at which point the electric potential would be essentially zero, or it may at a reference point that has been arbitrarily assigned a electric potential of zero.

Related terms:

For a list of other related terms see: electric field

Symbol: V

SI units: volts = joules / coulomb = newton × meters / coulomb

Remarks:

Electric potential is independent of the path taken.

There is no such thing as an absolute value of electric potential; only changes in electric potential are meaningful.

electric potential difference
voltage

Category: scalar quantity

Definition: The work required to move a unit positive electric charge between two points in an electric field.

Related terms: electric potential

For a list of other related terms see: electricity and magnetism, potential

Symbol: DV

SI units: volts = joules / coulomb = newton × meters / coulomb

Remarks:

Electric potential difference is independent of the path taken between two points.

electric reactance

Category: scalar quantity

Definition: In an alternating current circuit, that part of the electric impedance that is caused by electric capacitance or electric inductance and not by electric resistance

Related terms: inductive reactance, capacitive reactance

For a list of other related terms see: electric impedance

Symbol: X

SI units: ohms = newton × meter × seconds / coulomb²

Remarks:

The mathematical expression for electric reactance is:

X = (X_L - X_C)^½

where:

X = electric reactance

X_L = inductive reactance

X_C = capacitive reactance

electric resistance

Category: scalar quantity

Definition:

In an alternating current circuit, the the real part of the electric impedance.
In a direct current circuit, the ratio of the electric potential difference across a conductor to the electric current flowing through it.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: R

SI units: ohms = newton × meter × seconds / coulomb²

Remarks:

electric susceptance

Category: scalar quantity

Definition: The reciprocal of electric reactance.

Related terms:

For a list of other related terms see: electric impedance

Symbol: B

SI units: siemens = amperes / volt = coulomb² / newton × meter × second

Remarks:

electric susceptibility

Category: scalar quantity

Definition: The ratio of the electric polarization to the electric field strength in a dielectric medium in an electric field.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: c_e

SI units: dimensionless

Remarks:

The mathematical expression for electric susceptibility is:

c_e = P / E

where:

P = electric polarization

Electric susceptibility is equal to ε_r^-1 where ε_r is the relative permittivity of the dielectric medium.

electric vector potential

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

electrically charged

Category: phenomenon

Definition: Having an electric charge.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

electricity

Category: phenomenon

Definition: A fundamental entity of nature consisting of negative and positive kinds composed respectively of electrons and protons.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

electricity and magnetism
electromagnetism

Category: branch of physics

Definition: That branch of physics that deals with the phenomena related to electric charges and the motion of electric charges.

Related terms: see remarks

Symbol: not applicable

SI units: not applicable

Remarks:

The following phenomena are included:

electric fields produced by electric charges
magnetic fields produced by the motion of electric charges
propagation of electromagnetic waves

Following are some terms used in electricity and magnetism.

TERM	ELECTRIC	MAGNETIC
	electricity	magnetism
admittance	electric admittance
capacitance	electric capacitance
charge density	electric charge density
charge	electric charge	magnetic charge
circuit	electric circuit	magnetic circuit
conductance	electric conductance
conductivity	electric conductivity
constant	electric constant	magnetic constant
current density	electric current density
current	electric current
dipole moment	electric dipole moment	magnetic dipole moment
dipole	electric dipole	magnetic dipole
energy	electric energy	magnetic energy
field	electric field	magnetic field
field flux	electric field flux	magnetic field flux
field strength	electric field strength (E)	magnetic field strength (H)
field vector	electric field vector	magnetic field vector
flux	electric flux (Y)	magnetic flux (F)
flux density	electric flux density (D)	magnetic flux density (B)
force law	electric force law	magnetic force law
force	electric force	magnetic force
impedance	electric impedance
inductance	electric inductance
induction	electric induction
monopole		magnetic monopole
motive force	electromotive force (emf)	magnetomotive force
permeability		magnetic permeability
permittivity	electric permittivity
polarization	electric polarization
pole		magnetic pole
potential	electric potential	magnetic potential
potential difference	electric potential difference	magnetic potential difference
potential energy	electric potential energy
resistance	electric resistance
resistivity	electric resistivity
scalar potential	electric potential
susceptance	electric susceptance
susceptibility	electric susceptibility	magnetic susceptibility
vector potential	electric vector potential	magnetic vector potential (A)

electrodynamics

Category: branch of physics

Definition: That branch of physics that deals with the effects arising from the interactions between electric currents with magnets, with other electric currents, or with themselves as a consequence of the electromagnetic force.

Related terms: dynamics

For a list of other related terms see: electricity and magnetism, gauge theories, quantum field theories

Symbol: not applicable

SI units: not applicable

Remarks:

Electrodynamics is based on the observation that a moving electric charge produces a magnetic field and that an electric charge moving in a magnetic field will experience a force.

electromagnetic field

Category: field

Definition: A field in which there are interacting electric fields and magnetic fields.

Related terms: field

For a list of other related terms see: electricity and magnetism, field

Symbol: not applicable

SI units: not applicable

Remarks:

A changing electric field always produces a magnetic field and, conversely, a changing magnetic field always produces an electric field.

electromagnetic force

Category: fundamental force

Definition: A force between objects or particles that possess electric charge.

Related terms: electromagnetic interaction

For a list of other related terms see: electricity and magnetism, force, interaction

Symbol: ??

SI units: newtons

Remarks:

The electromagnetic force is one of the four fundamental forces:

electromagnetic force
gravitational force
strong force
weak force

The particle that mediates electromagnetic force is called the photon.

The range of a electromagnetic force is infinite.

If the electric charges have the same sign, the electromagnetic force is repulsive.

If the electric charges have opposite sign, the electromagnetic force is attractive.

electromagnetic interaction

Category: phenomenon

Definition: An interaction between objects or particles arising as a consequence of their electric charge.

Related terms: electromagnetic force

For a list of other related terms see: force, interaction

Symbol: not applicable

SI units: not applicable

Remarks:

All electrically charged particles participate in electromagnetic interactions.

electromagnetic mass

Category: scalar quantity

Definition: That part of the total inertia of an electrically charged object that arises from the electric charge of the object.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: ??

SI units: kilograms

Remarks:

The mathematical expression for the electromagnetic mass of an electric charge on a moving sphere is:

where:

m = electromagnetic mass

μ = permeability in the medium

e = amount of electric charge

a = radius of sphere

electromagnetic radiation

Category: phenomenon

Definition: Energy transmitted through space or through a medium in the form of electromagnetic waves.

Related terms: electromagnetic spectrum, light, photon

For a list of other related terms see: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

Electromagnetic radiation also exhibits particle-like properties.

The term light is sometimes loosely used in place of electromagnetic radiation of any frequency.

electromagnetic spectrum

Category: concept

Definition: The full range of frequencies of electromagnetic radiation.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

For descriptive purposes the electromagnetic spectrum is divided into approximate frequency ranges:

frequency hertz	wavelength meters	name	use
10¹	3 × 10⁷	...	power
10²	3 × 10⁶	...	power
10³	3 × 10⁵	ELF	...
10⁴	3 × 10⁴	VLF	induction heating
10⁵	3 × 10³	LF	long wave radio
10⁶	3 × 10²	MF	AM radio
10⁷	3 × 10¹	HF	short wave radio
10⁸	3 × 10⁰	VHF	television, FM radio
10⁹	3 × 10^-1	UHF	radar
10¹⁰	3 × 10^-2	SHF	radar, microwaves
10¹¹	3 × 10^-3	EHF	microwaves
10¹²	3 × 10^-4	far infrared	...
10¹³	3 × 10^-5	infrared	...
10¹⁴	3 × 10^-6	infrared	...
10¹⁵	3 × 10^-7	visible spectrum	...
10¹⁶	3 × 10^-8	ultraviolet	...
10¹⁷	3 × 10^-9	ultraviolet, x-rays	...
10¹⁸	3 × 10^-10	x-rays	...
10¹⁹	3 × 10^-11	x-rays	...
10²⁰	3 × 10^-12	gamma rays	...
10²¹	3 × 10^-13	gamma rays	...
10²²	3 × 10^-14	gamma rays	...
10²³	3 × 10^-15	gamma rays	...

electromagnetic theory of light
theory of light
wave model of light

Category: theory

Definition: The theory that light is an electromagnetic wave.

Related terms: wave-particle duality

Symbol: not applicable

SI units: not applicable

Remarks:

electromagnetic wave

Category: phenomenon

Definition: A system of electric fields and magnetic fields moving outward from a region where electric charges are accelerated.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

When particles of matter that possess electric charge decelerate, their kinetic energy decreases. An amount of energy equal to the decrease in kinetic energy is emitted in the form of what is called an electromagnetic wave.

electron
positron (antielectron)

Category: elementary particle

Definition: An electron is a charged lepton that belongs to the first generation of leptons.

An electron is a normal particle.

A positron is the antimatter equivalent of an electron.

The properties of an electron are:

property	value
electric charge	-1
rest mass	0.511 00 MeV / c² = 0.910 939 × 10^-30 kilogram
spin	1/2
mean lifetime	infinite

Related terms: elementary charge, muon, proton, tauon

For a list of other related terms see: leptons

For a list of other related terms see: particle categories

Symbol: e

SI units: not applicable

Remarks:

This is the only case in which an antiparticle has a distinct name.

Electrons interact though the electromagnetic force, weak force, and gravitational force but not through the strong force.

The electron is a fermion (since it has a spin of 1/2)

The electron is the lightest known particle that possesses a negative electric charge.

electron mass

Category: fundamental constant

Definition: The rest mass of an electron.

Related terms: none

Symbol: m_e

Values: 1 electron mass = 9.1094 × 10^-31 kilograms = 0.51100 MeV / c²

Remarks:

electron neutrino
electron antineutrino

Category: elementary particle

Definition: The neutrino that belongs to the first generation of leptons.

The properties of an electron neutrino are:

property	value
electric charge	0
rest mass	very small or 0
spin	1/2
mean lifetime	?? seconds

Related terms: leptons

Symbol: ν_e

SI units: not applicable

Remarks:

electronuclear force

Category: vector quantity

Definition: A force thought to have functioned in the very early universe that combined the electromagnetic force, weak force, and strong force.

Related terms: grand unified theory

For a list of other related terms see: force

Symbol: ??

SI units: newtons

Remarks:

electronvolt

Definition: A unit of measurement of energy equal to the work required to move an electron through a difference in potential of one volt.

Related terms: none

Symbol: eV

SI units: 1 electronvolt = 1.602 177 33 × 10^-19 joules (newton × meters)

Remarks:

The electronvolt unit is convenient at the atomic level.

electrostatic field

Category: ??

Definition: A force field produced by an electric charge at rest.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

electrostatic inductance

Category: scalar quantity

Definition: (to be completed at a later time)

For a list of other related terms see: electric induction

Symbol: ??

SI units: ??

Remarks:

The term can also be applied to a dielectric.

electrostatic induction

Category: phenomenon

Definition: The redistribution of electric charges in a object by an electric field.

For a list of other related terms see: electric induction

Symbol: not applicable

SI units: not applicable

Remarks:

electrostatic interaction

Category: phenomenon

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

electrostatics

Category: branch of physics

Definition: That branch of physics that deals with the forces between electric charges that are at rest.

Related terms: dynamics, statics

Symbol: not applicable

SI units: not applicable

Remarks:

If electric charges are not moving, they do not produce magnetic fields.

electroweak force

Category: fundamental force

Definition: A combination of the electromagnetic force and the weak force that may have occurred at an earlier time or may occur at very high energies.

Related terms: force

Symbol: ??

SI units: newtons

Remarks:

electroweak theory

Category: concept

Definition: Any gauge theory that unites the properties of electromagnetic interactions and weak interactions so that a single set of equations can be used to predict all of their characteristics.

Related terms: electroweak force, unified field theory

For a list of other related terms see: gauge theories, quantum field theories

Symbol: not applicable

SI units: not applicable

Remarks:

element

Category: concept

Definition:

In a geometric context, a geometric element.
In a chemical or particle context, one of the 100+ chemical elements.
In a matrix context, one of the values that make up the matrix.

Related terms: none

Symbol: varies

SI units: not applicable

Remarks:

elementary charge

Category: fundamental constant

Definition: The electric charge of one electron (negative) or one proton (positive).

Related terms: none

Symbol: e

Values: 1 elementary charge = 1.6022 × 10^-19 coulombs

Remarks:

elementary particle

Category: category of particle

Definition: A generic term for particles that, as far as is known, do not consist of simpler particles.

The categories of elementary particles are:

leptons
quarks
gauge bosons

Related terms: fundamental particle

For a list of other related terms see: particle categories

Symbol: varies

SI units: not applicable

Remarks:

The term elementary particles includes antiparticles as well as normal particles.

The term elementary particles includes particles that exhibit primarily wave-like properties (gauge bosons) as well as those that exhibit primarily particle-like properties (leptons and quarks).

The specific particles to which the term elementary particle applies has evolved over time. For example, from atom to proton to quark.

The number of elementary particles in each of the three categories is:

category	number
leptons	12
quarks	36
gauge bosons	12
total	60

Gravitons and Higgs bosons have not been included.

emf
electromotive force
electromotance

Category: scalar quantity

Definition: Emf is a measure of the strength of a source of electric energy.

Related terms:

Category: scalar quantity

Definition: The energy associated with a quantum state under defined conditions.

Related terms: none

Symbol: E

SI units: joules = newton × meters

Remarks:

The term energy level is often used when the quantum state itself is the intended meaning. This is incorrect usage because:

The energy of a given state may be changed by externally applied fields
There may be a number of states of equal energy in the system

entropy

Category: scalar quantity

Definition: The ratio of the change in the energy of a system to the thermodynamic temperature of the system.

dS = dE / T

where:

dS = differential change in entropy

dE = differential change in energy

T = thermodynamic temperature

Related terms: none

Symbol: S

SI units: joules / kelvin = newton × meters / kelvin

Remarks:

There is no such thing as an absolute entropy. Only changes in entropy are meaningful.

A change in entropy depends only on the end states of a system and is independent of the path taken by a process.

The entropy of a system is a measure of the unavailability of the internal energy of the system to do work in a cyclic process.

The overall entropy change in a reversible process is zero, but in any real process the entropy change will be positive when both the source and the destination of the energy are taken into account.

epoch

Category: concept

Definition: A period of time usually characterized by a distinctive series of events.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

equation

Category: notational convention

Definition: A statement that two mathematical expressions are equal.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

equation of state

Category: mathematical expression

Definition: An equation that relates the pressure, volume, and thermodynamic temperature of a substance.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The equation of state for an ideal gas is:

pV = nRT

where:

p = pressure

V = volume

n = number of moles

R = molar gas constant

Category: concept

Definition: Having the same potential.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

equivalence
equivalence principle

Category: principle

Statement: Inertial mass and gravitational mass are the selfsame property.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

erg

Definition: The unit of measurement of energy in the cgs system of units.

Related terms: none

Symbol: erg

SI units: 1 erg = 10^-7 joules (newton × meters)

Remarks:

ether

Category: concept

Definition: A hypothetical medium filling all of space and carrying electromagnetic radiation.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

This concept has been discarded.

Euclidean
Euclidean space
Euclidean space-time

Category: concept

Definition: Of, or based on, Euclidean geometry.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Euclidean geometry
parallel postulate

Category: branch of mathematics

Definition: A geometry based on Euclid's postulates including in particular the parallel postulate that states that through any point not on a given straight line there is exactly one straight line parallel to the given line.

Symbol: not applicable

SI units: not applicable

Remarks:

Euclidean geometry applies to surfaces that have no curvature, that is, planes in the ordinary sense.

Euler's equations

Category: theory

Definition: A set of three differential equations that describe the motion of a rigid object about a point using the principal axis through the point as coordinate axes.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of Euler's equations is:

I₁₁ - ω₂ω₃(I₂-I₃) = G₁

I₂₂ - ω₃ω₁(I₃-I₁) = G₂

I₃₃ - ω₁ω₂(I₁-I₂) = G₃

where:

I_n = moment of inertia about axis n

_n = derivative of ω_n with respect to time

ω_n = component of angular velocity about axis n

G_n = component of applied torque about axis n

even function

Category: concept

Definition: A mathematical function that has the following characteristic:

f(-x) = f(x)

Related terms: odd function

Symbol: not applicable

SI units: not applicable

Remarks:

A mathematical function can be even, odd, or neither.

The sine function is an odd function.

The cosine function is an even function.

e^x is neither odd nor even.

even parity

Category: concept

Definition: If a mathematical function does not change sign when are coordinates reversed, the mathematical function is said to have even parity.

f(x,y,z,) = f(-x,-y,-z)

Related terms: odd parity

For a list of other related terms see: parity

Symbol: not applicable

SI units: not applicable

Remarks:

event

Category: concept

Definition: Something that happens independently of the reference frame used to describe it.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

A flash of light
The coming together of two objects

event horizon

Category: phenomenon

Definition: The boundary around a black hole from inside of which neither matter nor radiation can escape.

Related terms: Schwarzschild radius

Symbol: not applicable

SI units: not applicable

Remarks:

The radius of the event horizon is equal to the Schwarzschild radius.

excited state

Category: concept

Definition: A state of a system that has a greater energy that the ground state of the system.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

exothermic reaction
exothermic

Category: phenomenon

Definition: A chemical reaction in which there is a transmission of energy from the reactants to the surroundings if the products of the chemical reaction are returned to the same temperature and pressure as originally existed.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Be careful; various disciplines use different signs.

experimental physics

Category: branch of physics

Definition: That branch of physics primarily concerned with observation and measurement as opposed to the development of theory.

Related terms: theoretical physics

Symbol: not applicable

SI units: not applicable

Remarks:

exponential decay

Category: phenomenon

Definition: Decay in which the rate of decay is proportional to the quantity of the decaying particle present in a sample.

Related terms: decay

Symbol: not applicable

SI units: not applicable

Remarks:

In a sample, the number of decays per second is:

A = λN = -dN / dt

where:

A = number of decays per second

λ = decay constant

N = number of particles in the sample

t = time

Integrating:

N = N₀e^-λt

where:

N₀ = number of particles at time 0

exponential rate of change
geometric progression

Category: concept

Definition: A rate of change, of a quantity, that is proportional to the amount of the quantity present.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

In equation form:

dq / dt = kq

where:

q = amount at time t

q₀ = initial amount

k = constant

t = time

t₀ = initial time

The constant (k) can be positive or negative.

extend

Category: concept

Definition: To stretch out in distance, area, volume, or time.

Related terms: extent, geometric element

Symbol: not applicable

SI units: not applicable

Remarks:

extensive

Category: concept

Definition: An extensive quantity or property is one that is proportional to the amount of the thing to which the quantity or property applies.

Related terms: intensive

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

Mass is extensive, temperature is not.

extent
extension

Category: concept

Definition: The distance, area, or volume over which something extends.

Related terms: geometric element

Symbol: not applicable

SI units: meters, meters², or meters³

Remarks:

external force

Category: vector quantity

Definition: A force that emanates from a source outside of the system under consideration.

Related terms: force

Symbol: ??

SI units: newtons

Remarks:

extrapolation

Category: mathematical operation

Definition: The estimation of the value of a mathematical function of a variable for a value of the variable outside the range of values for which the value of the mathematical function is known.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

extraterrestrial object

Category: generic term

Definition: An object that lies outside of the immediate vicinity of the earth.

Extraterrestrial objects include:

asteroids
black holes
comets
dust clouds
galaxies
galaxy clusters
gas clouds
globular clusters
moons
nebulae
stars

Statement: The curl of electric field strength is equal to minus the partial derivative of the magnetic flux density with respect to time.

Related terms: Maxwell's equations

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of Faraday's law is:

Faraday's law is one of Maxwell's equations.

Fermi-Dirac statistics

Category: ??

Definition: A statistical description of quantum mechanical systems in which the way in which particles can be distributed over the individual energy levels is restricted by the Pauli exclusion principle.

Related terms: Bose-Einstein statistics

Symbol: not applicable

SI units: not applicable

Remarks:

The type of statistics that apply to a particle is determined by the spin of the particle:

statistics	spin	particle category
Fermi-Dirac statistics	odd half integer	fermions
Bose-Einstein statistics	integer	bosons

fermion

Category: category of particle

Definition: A generic term for all particles that have odd half integer spin.

Related terms:

For a list of other related terms see: particle categories

Symbol: ??

SI units: not applicable

Remarks:

Leptons, quarks, and baryons (which consist of quarks) have odd half integer spin and are therefore fermions.

The distribution of fermions over the individual energy levels of a system is restricted by the Pauli exclusion principle and therefore fermions obey Fermi-Dirac statistics.

ferromagnetic

Category: concept

Definition: A property of certain solid substances that have a large positive magnetic susceptibility and therefore are capable of being magnetized by weak magnetic fields.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Feynman diagram

Category: notational convention

Definition: A pictorial representation of specific elementary particles and their interactions.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

field

Category: concept

Definition: A line, surface, or space in which a given quantity is associated with each point of the line, surface, or space.

The said quantity can be called the field quantity.

Symbol: not applicable

SI units: not applicable

Remarks:

The space may have any number of dimensions.

The field quantity may be a tensor quantity which, of course, includes a scalar quantity and a vector quantity.

In many important cases, the field quantity results from the presence of another quantity such as a mass or electric charge.

In many important cases, the field quantity is a force, that is of course a vector, in which case the field is a said to be a force field and a vector field.

In many important cases, the field quantity can be described by wave functions, in which case the field is said to be a wave field.

field energy

Category: scalar quantity

Category: fundamental constant

Definition: A dimensionless quantity formed from the four basic physical constants:

the electric charge of an electron
the speed of light
the Planck constant
the permittivity of free space.

Related terms: none

Symbol: α

Values: 7.297 353 1 » 10^-3 @ 1 / 137 (dimensionless)

Remarks:

The fine structure constant is a measure of the strength of the electromagnetic interaction.

The fine structure constant is a function of several other fundamental constants:

α = e² / 2hcε₀

where:

e = electric charge of an electron

first law of thermodynamics

Category: law

Statement: The net change in internal energy of a closed system is equal to the heat added to the system less the work done by the system.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

fission
nuclear fission

Category: phenomenon

Definition: The splitting of a nucleus into two or more parts of comparable mass.

Related terms: decay, fusion

Symbol: not applicable

SI units: not applicable

Remarks:

Fission is normally accompanied by the release of neutrons and gamma rays (photons).

The energy of the fission products is usually very large.

flavor

Category: concept

Definition: The type of a quark is referred to as its flavor.

There are exactly six types of quarks and therefore six flavors. These occur in three generations each of which has two members.

generation	electric charge = +2/3	electric charge = -1/3
1st	up quark	down quark
2nd	charmed quark	strange quark
3rd	top quark	bottom quark

Related terms: color, leptons, quantum flavordynamics, quarks

Symbol: ??

SI units: not applicable

Remarks:

fluid

Category: generic term

Definition: Fluid is a generic term for a liquid or a gas.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

fluid displacement

Category: scalar quantity

Definition: The amount of liquid displaced by a submerged or floating object.

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

fluid dynamics

Category: branch of physics

Definition: That branch of physics that deals with the properties and behavior of fluids that are in motion.

Related terms: fluid mechanics, fluid statics

Symbol: not applicable

SI units: not applicable

Remarks:

fluid mechanics

Category: branch of physics

Definition: That branch of physics that deals with the properties and behavior of fluids.

Symbol: not applicable

SI units: not applicable

Remarks:

Fluid mechanics can be divided in to two parts:

fluid statics
fluid dynamics

fluid statics

Category: branch of physics

Definition: That branch of physics that deals with the properties and behavior of fluids that are not in motion.

Related terms: fluid dynamics, fluid mechanics

Symbol: not applicable

SI units: not applicable

Remarks:

fluidity

Category: property

Definition: The reciprocal of dynamic viscosity.

Related terms: none

Symbol: φ

SI units: poise^-1 = meters² / newton × second

Remarks:

flux
flow

Category: scalar quantity

Definition:

The strength of a force field.
The transmission of a scalar quantity.
The rate of transmission of a scalar quantity.

Related terms: electric flux, magnetic flux, luminous flux

Symbol: varies

SI units: varies

Remarks:

flux density

Category: scalar quantity

Definition: The rate of flow of a vector field through an element of area per unit of area.

Related terms: vector field strength

Symbol: ??

SI units: not applicable

Remarks:

Flux density at a point is equal to the dot product of the vector field strength and the surface element. In other words, it is equal to the component of the vector field strength that is perpendicular to the surface element multiplied by the area of the surface element.

Category: phenomenon

Definition: Convection in which the movement of the fluid is caused predominantly by an outside force

Related terms: natural convection

Symbol: not applicable

SI units: not applicable

Remarks:

Fourier analysis

Category: mathematical operation

Definition: Computation of the coefficients in a Fourier series.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Fourier integral

Definition: The limiting form of a Fourier series when the period is made indefinitely great.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Fourier series

Category: mathematical expression

Definition: An infinite series of sine and cosine terms with known coefficients, the sum of which terms approximates a given periodic function.

Related terms: Fourier analysis

Symbol: not applicable

SI units: not applicable

Remarks:

Fourier transform

Definition: The result of the following mathematical operation in which a mathematical function of one variable (x) is changed to a mathematical function of a different variable(s).

F(s) =

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Fourier's theorem

Category: theorem

Statement: Any periodic function can be expressed as the sum of an infinite series of sine and cosine terms.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

fps system of units
foot-pound-second system of units
British system of units
English system of units

Category: system of units

free space

Category: concept

Definition: A space that contains no particles and no force fields .

Related terms: vacuum

Symbol: not applicable

SI units: not applicable

Remarks:

An absolute vacuum contains no particles but may contain a force field .

The values of the properties possessed by free space may be:

zero (e.g. thermodynamic temperature)
unity (e.g. refractive index)
maximum possible (e.g. speed of light)
specific values (e.g. permeability and permittivity)

free state

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Following are the names of some fundamental constants. See the individual terms for values:

Avogadro constant
Boltzmann constant
electric charge of an electron
fine structure constant
gravitational constant
mass of an electron
molar gas constant
permeability of free space
permittivity of free space
Planck constant
speed of light
Stefan-Boltzmann constant

fundamental force

Category: vector quantity

Definition: Any one of the four fundamental forces:

strong force
electromagnetic force
weak force
gravitational force

or a combination of one or more of the four that may have existed at an earlier time or that may exist at very high energies.

Related terms: force

Symbol: varies

SI units: newtons

Remarks:

The following are the approximate relative strengths of the fundamental forces:

force	relative strength^*	mediating particles
strong force	1	mesons / gluons
electromagnetic force	10^-2	photons
weak force	10^-9	intermediate vector bosons
gravitational force	10^-38	gravitons

* Approximate, for two protons in a nucleus.

fundamental frequency

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

fundamental particle

Category: generic term

Definition: A generic term for particles that, as far as is known, do not consist of simpler particles.

Related terms: elementary particle

Symbol: not applicable

SI units: not applicable

Remarks:

You may notice that this definition is the same as the one given for elementary particle. As the knowledge of physics has progressed, there has been a continuing attempt to select a categorical term for all of the simplest known particles. This has lead to some confusion.

In this glossary, we prefer to use the term elementary particle to refer to all the simplest known particles.

The distinction that is sometimes made is that elementary particles refers to hadrons not quarks and fundamental particle refers to quarks, not hadrons. We find this distinction more confusing than edifying and employ only the term elementary particle in this glossary.

fundamental quantity

Category: concept

Definition: (to be completed at a later time)

Related terms: base quantity, fundamental, quantity

Symbol: not applicable

SI units: not applicable

Remarks:

Force, length, mass, and time are interdependent; that is, one of them can be defined in terms of the other three.

Force, length, mass, and time are not absolutes; they are dependent upon the reference frame.

fusion

Category: phenomenon

Definition: A nuclear reaction between light atomic nuclei resulting in a conversion of mass to energy

Related terms: binding energy, fission

Symbol: not applicable

SI units: not applicable

Remarks:

Fusion is accompanied by the release of gamma rays (photons) and sometimes of neutrons.

The energy of the fusion products is very large.

g

galaxy

Category: object

Definition: A more or less organized system of stars and nebulae containing typically on the order of 10¹¹ stars in a space typically on the order of 10⁵ light-years across and usually separated from other groups of stars by 10⁵ light-years or more.

Related terms: cluster of galaxies

Symbol: not applicable

SI units: not applicable

Remarks:

Galaxies are often classified according to the arrangement of the stars in them:

spiral
regular spiral
barred spiral
elliptical
irregular

There are thought to be on the order of 10¹¹ galaxies in the universe.

Examples:

Milky Way: the galaxy in which the earth is located. It is thought to be a typical regular spiral galaxy.

Large Magellanic Cloud: a small irregular galaxy in the local galaxy cluster located about 600,000 light-years from the Milky Way.

Andromeda galaxy: a galaxy in the local galaxy cluster thought to be similar to the Milky Way located about 2,000,000 light-years from the Milky Way.

Galilean transformation
Galilean transformation equations

Category: mathematical operation

Definition: The set of equations, applicable in classical mechanics, that transform the coordinates of an event in one inertial reference frame to the coordinates of the event in a second inertial reference frame that is in motion with respect to the first inertial reference frame.

Related terms: Lorentz transformation equations

Symbol: not applicable

SI units: not applicable

Remarks:

In the simple case of two inertial reference frames with similarly oriented Cartesian coordinate systems moving along their common x axes, the equations for the Galilean transformation are:

Dx' = x - vDt

Dy' = Dy

Dz' = Dz

Dt' = Dt

where:

primed coordinates are in the moving frame

unprimed coordinates are in the lab frame

v = the speed of the moving frame relative to the lab frame

gamma ray
gamma radiation

Category: phenomenon

Definition: Electromagnetic radiation with frequency of the order of 10²¹ to 10²² hertz.

Symbol: not applicable

SI units: not applicable

Remarks:

Nuclei emit gamma rays when they decay from an excited state to a lower energy level.

Most gamma rays have energies in the range 10⁴ to 10⁶ eV, but some gamma rays of cosmic origin with energies up to 10⁸ eV have been detected. These are very high energies.

gas

Category: substance

Definition: Any fluid that expands to fill any volume, however large, without any change of phase.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

If the temperature of the fluid is below its critical temperature, the fluid is also called a vapor; especially if it is in equilibrium with a liquid phase.

gauge boson
gauge particle
field particle
mediating particle
mediator

Category: category of particle

Definition: A generic term for all elementary particles that mediate particle interactions.

The gauge bosons and the forces they mediate are:

gauge boson	force
gluons	strong force
photons	electromagnetic force
intermediate vector bosons	weak force
gravitons	gravitational force

Related terms: boson, particle

Related terms:

For a list of other related terms see: field, gauge transformation, particle categories

Symbol: not applicable

SI units: not applicable

Remarks:

There are three principal categories of elementary particles:

leptons
quarks
gauge bosons

All gauge bosons have spin +1.

gauge field

Category: generic term

Definition: A wave field in which the field quantity is gauge invariant.

Related terms: invariant, wave

For a list of other related terms see: gauge transformation, field

Symbol: not applicable

SI units: not applicable

Remarks:

Category: ??

Definition: (to be completed at a later time)

Related terms: none

For a list of other related terms see: gauge transformation

Symbol: not applicable

SI units: not applicable

Remarks:

gauge theory

Category: generic term

Definition: Any quantum field theory in which all measurable quantities remain unchanged under a gauge transformation.

Related terms: gauge transformation, theory

For a list of other related terms see: gauge transformation, quantum field theory

Symbol: not applicable

SI units: not applicable

Remarks:

In gauge theories, particle interactions (forces) are mediated by gauge bosons.

force	mediating gauge bosons
strong force	gluons
electromagnetic force	photons
weak force	intermediate vector bosons
gravitational force	gravitons

Gauge theories are believed to provide a basis for a description of all elementary particle interactions.

Gauge theories and the interactions (forces) that they cover include:

gauge theory	force
electrodynamics	electromagnetic force
electroweak theories	electromagnetic force and weak force
general relativity	gravitational force
grand unified theories	all
quantum chromodynamics	strong force
quantum flavordynamics	weak force

gauge transformation

Category: mathematical operation

Definition: A mathematical transformation in which the phases of the wave function that describes the field quantity of a wave field are altered by an amount that is a function of space and time.

Symbol: not applicable

SI units: not applicable

Remarks:

The term "gauge change" was introduced originally by H. Weyl and meant "change in length", the common meaning of gauge being size or length. It was later realized that the idea of changes in length in the circumstances that were being contemplated was not valid. The mathematics were then changed to include the square root of -1 as a factor with the result that the change was a change in phase rather than of length. Nevertheless the word "gauge" continues to be used.

gauss

Definition: The unit of measurement of magnetic flux density in the cgs electromagnetic system of units.

Related terms: none

Symbol: G

SI units: 1 gauss = 10^-4 tesla (newton × second / coulomb × meter)

Remarks:

Gauss's law

Category: law

Statement: The divergence of electric field strength at a point is proportional to the electric charge density at that point.

Symbol: not applicable

SI units: not applicable

Remarks:

In a vacuum, Gauss's law may be written:

where:

ρ = electric charge density

Gauss's law in an integral form can be stated: For any closed surface drawn in an electric field. the integral of the normal component of the electric field strength over the surface is equal to the total electric charge enclosed within the surface.

In a vacuum, the integral form of Gauss's theorem may be written:

where:

da = element of surface

dτ = element of volume

Q_enc = net enclosed electric charge

Analogous statements may be made for gravitational fields, and magnetostatic fields.

Gaussian system of units

Category: system of units

Definition: One of the variations of the cgs system of units.

Related terms:

For a list of other related terms see: systems of units

Symbol: not applicable

SI units: not applicable

Remarks:

In the Gaussian system of units, units from the cgs electrostatic system of units are used to measure electric quantities and units from the cgs electromagnetic system of units are used to measure magnetic quantities.

Gay-Lussac's law

Category: law

Statement: The pressure of a fixed amount of gas is directly proportional to its absolute temperature of the gas when the volume is kept constant.

Related terms: Boyle's law, Charles's law, ideal gas

Symbol: not applicable

SI units: not applicable

Remarks:

Gay-Lussac's law is only approximately true for actual gases.

general theory of relativity
Einstein's general theory of relativity

Category: theory

Definition: A theory of motion that deals with accelerated reference frames.

Related terms: relativity

For a list of other related terms see: gauge theories, quantum field theories, special theory of relativity

Symbol: not applicable

SI units: not applicable

Remarks:

The general theory of relativity was first published by Einstein in 1917.

The general theory of relativity is not limited, as the special theory of relativity is, to reference frames that are in uniform motion, and therefore is more general than the special theory of relativity.

generalized coordinates

Category: concept

Definition: Coordinates that describe the motion of a system without specifying the exact nature of the system.

Related terms: generalized momentum, degrees of freedom

Symbol: q_i

SI units: not applicable

Remarks:

There must be one generalized coordinate for each degree of freedom.

generalized momentum
generalized linear momentum

Category: vector quantity

Definition: Linear momentum expressed in terms of generalized coordinates.

Related terms: none

Symbol: p_i

SI units: kilogram × meters / second

Remarks:

The mathematical expression for the ith component of a generalized momentum is:

p_i = ¶L / ¶_i

where:

p_i = ith scalar component of generalized linear momentum

q_i = generalized coordinate

L = Lagrangian function

generations of particles

Category: concept

Definition: It is a remarkable fact that there are exactly six leptons and six quarks (and their antiparticles), that can be categorized into exactly three "generations" in which each generation of each category have exactly two members:

generation	charged leptons	neutrinos	quarks	quarks
electric charge	-1	0	+2/3	-1/3
1st	electron	electron neutrino	up quark	down quark
2nd	muon	muon neutrino	charmed quark	strange quark
3rd	tauon	tauon neutrino	top quark	bottom quark

Related terms:

For a list of other related terms see: particle categories

Symbol: not applicable

SI units: not applicable

Remarks:

Only the first generation of elementary particles occur in ordinary matter.

The term normal particle covers all three generations.

generic term

Category: concept

Definition: A term that encompasses a number of terms that share common attributes.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

Gravitational field and electric field are specific terms. Field is a generic term that encompasses, gravitational field, electric field, and other specific fields.

geodesic

Category: concept

Definition: The path with minimum (or maximum) distance between two points in a mathematically defined space.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

In a Cartesian space, a geodesic is a straight line.

On a sphere a geodesic is a great circle.

geometric element

Category: concept

Definition: A point, line, surface, or space.

Related terms: element, extent, geometry

Symbol: not applicable

SI units: not applicable

Remarks:

geometric mean

Definition: The nth root of the product of a set of n numbers.

Related terms:

For a list of other related terms see: arithmetic mean

Symbol: ??

SI units: not applicable

Remarks:

The geometric mean of the numbers a₁ ,a₂ ,a₃ ,..., a_n is:

(a₁a₂a₃...a_n)^{1 / n}

geometry

Category: branch of mathematics

Definition: Of, or relating to, the measurement, properties, and relationships of points, lines, angles, surfaces, and spaces.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Glashow-Weinberg-Salam theory
GWS theory
standard model

Category: theory

Definition: A unified field theory of electromagnetic interactions and weak interactions.

Related terms:

For a list of other related terms see: gauge theories, quantum field theories

Symbol: not applicable

SI units: not applicable

Remarks:

global gauge invariance

Category: concept

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

global gauge transformation

Category: concept

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

globular cluster

Category: phenomenon

Definition: A dense, spherical, and usually old cluster of stars.

Related terms: galaxy, nebula

Symbol: not applicable

SI units: not applicable

Remarks:

gluon

Category: category of particle

Definition: A generic term for all elementary particles that mediate the strong interaction.

The properties of an gluon are:

property	value
electric charge	0
rest mass	0
spin	1
mean lifetime	infinite

For a list of other related terms see: particle categories

Symbol: ??

SI units: not applicable

Remarks:

A gluon is analagous to a photon.

There are eight gluons.

All gluons are gauge bosons.

gluon field

Category: field

Definition: A field associated with a gluon.

Related terms: boson field

For a list of other related terms see: field

Symbol: not applicable

SI units: not applicable

Remarks:

gradient

Category: vector quantity

Definition: The derivative (slope) of a mathematical function in the direction of maximum ascent.

Related terms:

For a list of other related terms see: del operator

Symbol: grad or Ñ

SI units: not applicable

Remarks:

If:

f = f(x,y,z)

then

grad f = Ñf = i^¶f/¶x + j^¶f/¶y + k^¶f/¶z

gram

Definition: A unit of measurement of mass.

Related terms: none

Symbol: gm

SI units: 1 gram = 10^-3 kilogram

Remarks:

grand unified theory
GUT

Category: theory

Definition: A unified field theory that unites the properties of the strong interaction, electromagnetic interaction, and weak interaction so that a single set of equations can be used to predict all of their characteristics.

Related terms:

For a list of other related terms see: gauge theories, quantum field theories

Symbol: not applicable

SI units: not applicable

Remarks:

The grand unified theory is a gauge theory.

Ultimately, it should also include gravitation. It is not known whether such a theory can be constructed.

gravitation
gravity

Category: concept

Definition: The mutual attraction of all objects that possess mass.

Symbol: not applicable

SI units: not applicable

Remarks:

Gravitation is independent of strong interactions, electromagnetic interactions, and weak interactions.

gravitational constant

Category: fundamental constant

Definition: A fundamental constant that relates the force between two objects due to gravitation, the masses of the two objects, and the distance that separates the two objects.

Related terms:

For a list of other related terms see: gravitation

Symbol: G

Values: 6.672 59 × 10^-11 newton × meters² / kilogram²

Remarks:

Gravitational mass is the charge that produces the gravitational force.

gravitational field

Category: phenomenon

Definition: The force field produced by a mass.

Related terms:

For a list of other related terms see: field, force, gravitation

Symbol: not applicable

SI units: not applicable

Remarks:

gravitational field strength

Category: vector quantity

Definition: The force that a gravitational field exerts on a test mass per unit of test mass.

Related terms: field

For a list of other related terms see: gravitation

Symbol: ??

SI units: newtons

Remarks:

gravitational force
force of gravity

Category: fundamental force

Definition: A force between objects or particles that possess mass.

Related terms: gravitational interaction

For a list of other related terms see: force, gravitation, interaction

Symbol: ??

SI units: newtons

Remarks:

The gravitational force is one of the four fundamental forces:

electromagnetic force
gravitational force
strong force
weak force

The particle that mediates gravitational force is called the graviton.

The range of a gravitational force is infinite.

The gravitational force is always attractive.

gravitational interaction

Category: phenomenon

Definition: An interaction between objects or particles arising as a consequence of their mass.

Related terms gravitational force

For a list of other related terms see: force, gravitation, interaction

For a list of other related terms see: gravitation

Symbol: not applicable

SI units: not applicable

Remarks:

All particles that possess mass participate in gravitational interactions.

gravitational mass
gravitational charge

Category: scalar quantity

Definition: The property of an object that determines the strength of the gravitational force that the object generates.

Related terms: charge, inertial mass, equivalence principle

For a list of other related terms see: gravitation, interaction

Symbol: m

SI units: kilograms

Remarks:

Gravitational mass is the charge that produces the gravitational force.

It is believed that gravitational mass and inertial mass are the selfsame property.

gravitational potential
gravitational potential energy

Category: scalar quantity

Definition: The work required to move a unit of mass from infinity to a point in a gravitational field

Related terms: potential

For a list of other related terms see: gravitation

Symbol: ??

SI units: joules = newton × meters

Remarks:

gravitino

Category: hypothetical particle

Definition: The supersymmetric partner of the graviton.

Related terms: supersymmetry

For a list of other related terms see: gravitation

Symbol: ??

SI units: not applicable

Remarks:

graviton

Category: hypothetical particle

Definition: A hypothetical elementary particle that mediates gravitational interactions.

Related terms: gauge bosons

For a list of other related terms see: gravitation, particle categories

Symbol: ??

SI units: not applicable

Remarks:

A graviton is analagous to a photon.

A graviton is the quantum of the gravitational field and is thus a gauge boson.

The graviton is postulated to be its own antiparticle, to have zero electric charge, to have zero rest mass, and to have a spin of 2.

ground state

Category: concept

Definition: A state of a system that has the least possible energy.

Related terms: excited state

Symbol: ??

SI units: not applicable

Remarks:

A system may have more than one ground state with equal energies but different sets of quantum numbers.

There are two categories of hadrons:

baryons, which consist of exactly 3 quarks.
mesons, which consist of quark - antiquark pairs.

Examples:

The following particles are a few of the hadrons:

protons
neutrons

half-life

Category: scalar quantity

Definition: The time it takes for a quantity to decay to half its original amount.

Related terms: mean lifetime

Symbol: t₊

SI units: seconds

Remarks:

For exponential decay:

N = N₀e^-λt

where:

N = amount of quantity at time t

N₀ = amount of quantity at time 0

λ = decay constant

t = time

After a time equal to the half-life:

N / N₀ = 1/2 = e^-λt_½

® t_½ = (ln 2) / λ

Hamilton's equations of motion
canonical equations of motion

Category: theory

Definition: A set of first-order partial differential equations for a system of objects that relate the generalized coordinates and the generalized momenta of the system.

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of Hamilton's equations of motion are:

where:

H = Hamiltonian function

p_i = ith component of momentum

q_i = ith coordinate

Hamilton's equations of motion are a restatement of Lagrange's equations of motion with an emphasis on momenta rather than forces.

Hamilton's equations of motion are first-order differential equations, whereas Lagrange's equations of motion are second-order.

Hamilton's principle

Category: principle

Statement: Of all the possible paths along which a dynamic system may move from one point to another within a specified time interval, the actual path followed is that path that minimizes the time integral of the Lagrangian (the difference between the kinetic energy and the potential energy).

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of Hamilton's principle is:

ò (T-U) dt will be a minimum.

Hamiltonian function
Hamiltonian

Category: mathematical expression

Definition: A mathematical function that expresses the energy of a system in terms of generalized coordinates, generalized momenta, and time.

Symbol: H

SI units: not applicable

Remarks:

The mathematical expression of a Hamiltonian function is:

H = H(q_i, p_i, t)

where:

H = Hamiltonian function

q_i = ith generalized coordinate

p_i = ith component of generalized momentum

t = time

harmonic motion
sinusoidal motion

Category: phenomenon

Definition: A periodic motion that is composed of one or more simple harmonic motions.

Related terms: motion.

Symbol: not applicable

SI units: not applicable

Remarks:

head
pressure head

Category: pseudoscalar quantity

Definition: The height of a column of liquid (usually water) that is open to the atmosphere that will exactly balance a given pressure.

Related terms: none

Symbol: ??

SI units: meters

Remarks:

heat

Category: scalar quantity

Definition: Energy transferred or transmitted as a result of a temperature difference.

Related terms: work

For a list of other related terms see: energy

Symbol: Q

SI units: joules = newton × meters

Remarks:

There are three processes of heat transfer:

conduction
convection
electromagnetic radiation

Category: system of units

Definition: One of the variations of the cgs system of units.

Related terms:

For a list of other related terms see: systems of units

Symbol: not applicable

SI units: not applicable

Remarks:

The Heaviside-Lorentz system of units is a variation of the Gaussian system of units in which the permeability of free space has a value of 4π and the permittivity of free space has a value of 1 / 4π.

Heisenberg uncertainty principle
uncertainty principle
indeterminancy principle

Category: principle

Statement: There is a fundamental limit to the accuracy to which both the position and the velocity of a particle may be known simultaneously.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

If Dp_x is the uncertainty in the value of a component of momentum of a particle and Dx is the uncertainty in the corresponding coordinate of position at the same instant then:

Dp_x Dx ³ h / 2π

where h is the Planck constant.

Likewise, if DE is the uncertainty in the value of the energy of a particle and Dt is the uncertainty in the time interval during which the value of the energy is known then:

DE Dt ³ h / 2π

To put it another way, if one of the two values is known to be within certain limits, then it is not possible to know the other value to a greater accuracy than that given by the above equations.

This is not a matter of accuracy of measurement; it is a fundamental limit.

helicity

Category: quantum number

Definition: A quantum number used to specify the relative orientation of spin and linear momentum of massless particles.

Values are assigned as follows:

direction	helicity
same direction	+1
opposite direction	-1

Related terms: chiral state

Symbol: ??

Values: -1 or +1

Remarks:

For particles that possess mass, there is a very closely related term, chiral state or chirality.

It is a fundamental requirement of quantum mechanics that massless particles have their spins aligned in either the same direction or in the opposite direction to their linear momentum.

Neutrinos always have helicity -1 (opposite direction).

Antineutrinos always have helicity +1 (same direction).

helium

Category: chemical element

Definition: The chemical element having atomic number 2.

Related terms: hydrogen, lithium

Symbol: He

SI units: not applicable

Remarks:

There are five isotopes of helium. They have 1, 2, 3, 4, and 6 neutrons respectively.

Helium 4 (two protons + two neutrons) is the second most abundant chemical element in the universe.

henry

Definition: The unit of measurement of inductance in the SI system of units.

Related terms: none

Symbol: H

SI units: 1 henry = 1 weber / ampere = 1 newton × meter × seconds² / coulomb²

Remarks:

Hermitian conjugate

Definition: The matrix formed by taking the complex conjugate of each element of a matrix and transposing the result (exchanging rows and columns).

Related terms: none

Symbol: Ms (M dagger)

SI units: not applicable

Remarks:

Hermitian matrix

Category: concept

Definition: A matrix that equals the Hermitian conjugate of itself.

M = Ms

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

hertz

Definition: The unit of measurement of frequency in the SI system of units.

Related terms: none

Symbol: Hz

SI units: 1 hertz = 1 cycle / second

Remarks:

Higgs boson

Category: hypothetical particle

Definition: A gauge boson predicted by the Glashow-Weinberg-Salam theory.

Related terms: electroweak theory

Symbol: ??

SI units: not applicable

Remarks:

As of June 2001, the existence of the Higgs boson had not been confirmed.

The Higgs boson is predicted to have spin 0 and a large mass.

Higgs field

Category: field

Definition: The field associated with the Higgs boson.

Related terms: boson field

For a list of other related terms see: field

Symbol: not applicable

SI units: not applicable

Remarks:

Higgsino

Category: hypothetical particle

Definition: The supersymmetric partner of the Higgs boson.

Related terms: supersymmetry

Symbol: ??

SI units: not applicable

Remarks:

Hilbert space

Category: concept

Definition: A vector space for which a dot product is defined and that has the property that if a sequence of elements is such that any two members are arbitrarily close together if the members are chosen far enough along in the sequence, the sequence converges to a limit belonging to the vector space.

Related terms: matrix mechanics

Symbol: not applicable

SI units: not applicable

Remarks:

In matrix mechanics, the eigenfunctions of quantum mechanics are represented by orthogonal unit vectors in a Hilbert space.

homeomorphism
homeomorphic

Category: quality

Definition: A one-to-one mapping in topology between two figures that is continuous in both directions.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

homogeneous
nonhomogeneous

Category: concept

Definition: Having the same structure, composition, and characteristics throughout.

Related terms: isotropic

Symbol: not applicable

SI units: not applicable

Remarks:

In mathematics, homogeneous has a number of very specific meanings that are not included in this glossary.

Hooke's law

Category: law

Statement: When a object is subjected to a stress, the strain is proportional to the stress.

Related terms: modulus of elasticity

For a list of other related terms see: stress

Symbol: not applicable

SI units: not applicable

Remarks:

Hooke's law is only approximately true for some substances and even for those cases it is only true within limits.

horizontal

Category: concept

Definition: Parallel to, in the plane of, or operating in a plane parallel to a base line.

Related terms: vertical

Symbol: not applicable

SI units: not applicable

Remarks:

In common usage the base line is the horizon.

horizontal polarization

Category: phenomenon

Definition: Polarization of electromagnetic radiation in which the electric field vector is horizontal and the magnetic field vector is vertical.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

horsepower

Definition: A unit of measurement of power in the fps system of units.

Related terms: none

Symbol: hp

SI units: 1 hp = 745.7 watts (newton × meters / second)

Remarks:

Hubble constant

Category: empirical constant

Definition: The ratio of the recessional velocity of distant galaxies to their distance from the earth.

Related terms: none

Symbol: H₀

Values: 55 to 80 kilo meters / second × mega parsec

Remarks:

As of June 2001, the value of the Hubble constant is in dispute.

The reciprocal of the Hubble constant has the dimension of time and gives an indication of the age of the universe. The lower value (55) gives an age of 18 × 10⁹ years.

hydrogen

Category: chemical element

Definition: The chemical element having atomic number 1.

Related terms: deuterium, helium, lithium, tritium

Symbol: H

SI units: not applicable

Remarks:

There are three isotopes of hydrogen: hydrogen, deuterium, and tritium, having 0, 1, and 2 neutrons respectively.

hypercharge

Category: quantum number

Definition: A quantum number equal to the sum of baryon number and strangeness.

Related terms: none

Symbol: Y

Values: ??

Remarks:

Hypercharge is conserved in strong interactions and electromagnetic interactions but not in weak interactions.

hyperfine structure

Category: phenomenon

Definition: A closely spaced structure in the spectrum of an atom or molecule.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Hyperfine structure may be caused by:

multiple isotopes
the magnetic moment of a non-spherical nucleus
the interaction of the magnetic moments of the nucleus and the electrons

hyperon

Category: category of particle

Definition: A generic term for long-lived baryons other than the protons and neutrons.

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

Long-lived in this context means not decaying by strong interaction, i.e. particles with mean lifetimes greater than about 10^-24 seconds.

hypothesis

Category: generic term

Definition: A scientific proposition intended to explain a given set of phenomena, suggested as possibly true, and tentatively assumed in order to pursue the logical consequences.

Related terms: hypothetical

For a list of other related terms see: proposition

Symbol: not applicable

SI units: not applicable

Remarks:

A hypothesis is a proposition that is less well established than a theory and considered to be subject to verification.

hypothetical
conjectural
tentative

Category: concept

Definition: Suggested as possibly true and tentatively assumed in order to pursue the logical consequences.

Related terms: hypothesis

Symbol: not applicable

SI units: not applicable

Remarks:

hypothetical particle

Category: concept

Definition: A particle, the existence of which has been suggested but not proven.

Related terms: hypothetical

Symbol: not applicable

SI units: not applicable

Remarks:

hypothetical quantity

Category: concept

Definition: A quantity, the existence of which has been suggested but not proven.

Related terms: hypothetical

Symbol: not applicable

SI units: not applicable

Remarks:

hysteresis

Category: phenomenon

Definition: A delay in the change of an observed effect in response to a change in the mechanism producing the effect.

Related terms: elastic hysteresis

Symbol: not applicable

SI units: not applicable

Remarks:

i

ideal gas
perfect gas

Category: substance

Definition: An ideal gas is a hypothetical gas that would obey the following laws:

Avogadro's hypothesis
Boyle's law
Charles's law
Dalton's law
Gay-Lussac's law
ideal gas law
Joule's law

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

All of these laws are only approximately true for actual gases.

ideal gas law

Category: law

Definition: The equation of state for an ideal gas.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of the ideal gas law is:

PV = NRT

where:

P = absolute pressure
V = volume
N = number of moles
R = molar gas constant
T = absolute temperature

illuminance
illumination
intensity of illumination

Category: scalar quantity

Definition: The luminous flux incident on a given surface per unit of area.

Related terms: luminance, radiance

Symbol: E

SI units: lux = lumens / meter²

Remarks:

imaginary number

Category: concept

Definition: The square root of a negative number.

Related terms: complex number, real number

Symbol: i (the square root of -1)

SI units: dimensionless

Remarks:

Imaginary numbers are a subset of the complex numbers.

Examples:

The square root of -4 is 2i.

impedance

Category: scalar quantity

Definition: A measure of the opposition of a system to an oscillating force.

Related terms: electric impedance, mechanical impedance

Symbol: Z

SI units: varies

Remarks:

Impedance is similar in meaning to resistance.

impulse

Category: vector quantity

Definition: The change in momentum of a object produced by a force acting on the object for a (usually short) time interval .

Related terms: none

Symbol: ??

SI units: kilogram × meters / second

Remarks:

impulsive force

Category: vector quantity

y = f(x)

y is a dependent variable and x is an independent variable.

index of refraction
refractive index
absolute index of refraction
relative index of refraction

Category: property

Definition: A relative index of refraction is the ratio of the phase velocity of light in one medium to the phase velocity in another medium.

An absolute index of refraction is the ratio of the phase velocity of light in a medium to the phase velocity of light in a vacuum

Related terms: refraction

Symbol: n

SI units: dimensionless

Remarks:

induced emf

Category: scalar quantity

inertial force
inertia force

Category: pseudoforce

Definition: A pseudoforce that arises because the reference frame of the observer is not an inertial reference frame.

Related terms: force

Symbol: F

SI units: newtons

Remarks:

inertial mass

Category: scalar quantity

Definition: The property of an object that determines the acceleration that an object undergoes when acted upon by a force.

Related terms: gravitational mass, equivalence principle

Symbol: m

SI units: kilograms

Remarks:

It is believed that gravitational mass and inertial mass are the selfsame property.

inertial reference frame
noninertial reference frame
newtonian system

Category: concept

Definition: An inertial reference frame is a reference frame that is neither accelerating nor rotating. In other words, it must be in uniform motion.

Related terms: Newton's first law

For a list of other related terms see: reference frame

Symbol: not applicable

SI units: not applicable

Remarks:

If Newton's first law holds in a reference frame, then the reference frame must be an inertial reference frame.

There is no preferred inertial reference frame. This is equivalent to saying that there is no such thing as an absolute velocity.

infinite

Category: concept

Definition: Unlimited as to amount, extent, or number.

Related terms: none

Symbol: ¥

SI units: not applicable

Remarks:

There are several orders of infinite, the smallest being the countably infinite (aleph null, ¥₀).

infinite series

Category: mathematical expression

Definition: A mathematical expression that consists of the sum of an infinite number of terms each of which is given by some mathematical expression or rule that is a function of its position in the series.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

inflation

Category: hypothesis

Definition: A brief and rapid expansion of the universe at a very early time associated with the phase transition that separated the strong force from the electroweak force.

Related terms: Big Bang, symmetry breaking

Symbol: not applicable

SI units: not applicable

Remarks:

infrared

Category: quality

Definition: Electromagnetic radiation with frequency of the order of 10¹² to 10¹⁴ hertz.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

integer
integer number

Category: concept

Definition: The numbers 0, ±1, ±2, ±3, a

Related terms: number

Symbol: n

SI units: not applicable

Remarks:

The integers are a superset of the natural numbers and a subset of the rational numbers.

integral

Definition: The result of a mathematical integration

Related terms: definite integral, indefinite integral

Symbol: not applicable

SI units: not applicable

Remarks:

integration

Category: mathematical operation

Definition: The mathematical operation of finding a mathematical function whose differential is known.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

intensity

Category: generic term

Definition: The rate of impingement of a quantity such as radiation on a unit of extent, mass, or charge.

Related terms: none

Symbol: varies

SI units: varies

Remarks:

A particular intensity may be a scalar quantity or a vector quantity.

intensive

Category: concept

Definition: An intensive quantity or property is one that is the same regardless of the amount of the thing to which the quantity or property applies.

Related terms: extensive

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

Temperature is intensive, mass is not.

interaction
particle interaction

Category: concept

Definition: Any process in which particles exert forces on each other.

Symbol: not applicable

SI units: not applicable

Remarks:

There are four fundamental interactions:

force	particles affected
strong force	quarks, hadrons
electromagnetic force	quarks, hadrons, charged leptons
weak force	quarks, hadrons, all leptons
gravitational force	all

intermediate vector boson

Category: category of particle

Definition: A generic term for all elementary particles that mediate the weak interaction.

For the properties of intermediate vector bosons, see the individual particle:

W+ particle
W- particle
Z0 particle

Related terms: gauge bosons

For a list of other related terms see: particle categories

Symbol: W, Z

SI units: not applicable

Remarks:

An intermediate vector boson is analagous to a photon.

internal energy
thermal energy

Category: scalar quantity

Definition: The sum of the potential energies of the particle interactions and the kinetic energies of the particles within an amount of substance.

Related terms:

For a list of other related terms see: energy

Symbol: U

SI units: joules = newton × meters

Remarks:

The term internal energy is applied only on a macro scale. On a micro scale, the component energies would be separately considered.

The internal energy of a object may be changed by both of the processes of work and heat.

internal quantum number

Category: concept

Definition: A quantum number associated with any quantized property of a particle.

Related terms: quantum number

Symbol: varies

SI units: dimensionless

Remarks:

The complete set of internal quantum numbers is:

electric charge
baryon number
lepton number
spin quantum number
upness
downness
strangeness
charm
beauty
truth

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

invariance
symmetry

Category: property

Definition: The property of remaining unchanged under certain mathematical transformations such as:

changing the orientation in space
changing the sign of the electric charge
changing the phase of a wave function
changing the direction of time flow
space inversion

Symbol: not applicable

SI units: not applicable

Remarks:

invariance principle
symmetry principle

Category: principle

Statement: In order for a physical law to be correct, the law must be the same in all reference frames.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

invariant

Category: concept

Definition: Unchanged by a mathematical operation.

Related terms: symmetry

Symbol: not applicable

SI units: not applicable

Remarks:

Invariant may be compared with conserved which means unchanged by a physical process.

If the value of a quantity is unchanged by a mathematical operation on a system then:

the quantity is said to be invariant under the mathematical operation
a symmetry is said to exist
the quantity is said to be a symmetric quantity under the mathematical operation
the mathematical operation is said to be a symmetry operation.

inverse of a matrix

Definition: A mathematical transformation of a matrix that when multiplied by the original matrix yields the unit matrix.

Related terms: none

Symbol: M^-1where M is the original matrix

SI units: not applicable

Remarks:

The mathematical expression of the definition is:

MM^-1 = U

where:

M = original matrix

M^-1 = inverse of the matrix

U = unit matrix

The inverse of a matrix is computed by dividing each element of the adjoint of the matrix by the determinant of the matrix.

The original matrix must be a square matrix.

inverse square law

Category: concept

Definition: A law relating the intensity of an effect to the reciprocal of the square of the distance from the cause.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

Coulomb's law
Newton's law of universal gravitation

inversion

Category: mathematical operation

Definition: Reversal of sign or direction.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

ion
ionized

Category: object

Definition: An electrically charged atom or molecule.

Related terms: anion, cation

For a list of other related terms see: atom

Symbol: not applicable

SI units: not applicable

Remarks:

ionic bond

Category: phenomenon

Definition: A chemical bond in which the "shared" electrons spend most of the time around one of the atoms thereby creating an polarization with the result that the atoms are held together by electromagnetic force.

Related terms: covalent bond

Symbol: not applicable

SI units: not applicable

Remarks:

ionization

Category: process

Definition: The process of forming ions.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

If A is an atom then ionization can be represented by:

A ® A⁺ + e^-

where:

A⁺ = ion

e^- = electron

ionization energy
ionization potential

Category: scalar quantity

Definition: The minimum energy required for ionization.

Related terms: none

Symbol: I

SI units: joules = newton × meters

Remarks:

The ion and the electron must be far enough apart for their electrostatic interaction to be negligible.

There must be no net increase in kinetic energy.

ionizing radiation

Category: phenomenon

Definition: Any radiation that causes the ionization of the medium through which it passes.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Ionizing radiation may consist of high energy particles or of electromagnetic radiation.

irradiance

Category: scalar quantity

Definition: The radiant flux incident upon a given surface per unit of area.

Related terms: radiant exitance, illuminance

For a list of other related terms see: radiant flux

Symbol: E

SI units: watts / meter² = newtons / meter× second

Remarks:

irrational number

Category: concept

Definition: A real number that can not be expressed as the quotient of two integers.

Related terms: rational number

Symbol: not applicable

SI units: not applicable

Remarks:

Irrational numbers are a subset of the real numbers.

isentropic
isentropic process
reversible process

Category: concept

Definition: Occurring without any increase in entropy.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

On a macroscopic scale, an isentropic process is a theoretical ideal; no actual macroscopic processes are isentropic.

ISO

Category: common term

Definition: An acronym for The International Organization for Standardization.

Related terms: SI Units

Symbol: not applicable

SI units: not applicable

Remarks:

isolated system

Category: concept

Definition:

In thermodynamics, a system that can not exchange mass or energy with the surroundings.

In classical mechanics, a system of objects in which the only forces present are those between the objects in the system.

Related terms: closed system, open system

Symbol: not applicable

SI units: not applicable

Remarks:

isospin
isotopic spin
isobaric spin
i-spin

Category: quantized property

Definition: A quantized property of elementary particles.

Related terms: spin

Symbol: I

SI units: dimensionless

Remarks:

Isospin should not be confused with spin.

isospin quantum number

Category: quantum number

Definition: An quantum number associated with the isospin of a particle.

Related terms: quantum number

Symbol: ??

Values: integers or half-integers

Remarks:

isothermal
isothermal process

Category: concept

Definition: A process that occurs at constant temperature.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

isotope

Category: substance

Definition: Any of two or more species of a chemical element with the same number of protons but a different number of neutrons in the nucleus.

Related terms:

For a list of other related terms see: atom

Symbol: not applicable

SI units: not applicable

Remarks:

The chemical properties of the isotopes of an chemical element are the same.

Hydrogen has three isotopes:

ordinary hydrogen

deuterium

tritium

where the subscripts indicate the number of protons and the superscripts indicate the total number of nucleons (protons plus neutrons) in the nucleus.

isotopic parity
G-parity

Category: quantum number

Definition: A quantum number associated with elementary particles that have zero baryon number and +1 strangeness.

Related terms: none

Symbol: ??

Values: -1, 0, or +1

Remarks:

G-parity is conserved in strong interactions only.

k

kelvin
kelvin scale
degree kelvin

Definition: The base unit of thermodynamic temperature in the SI system of units.

The ISO definition is: "The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water" (1967).

Related terms: Celsius, Fahrenheit

Symbol: K

SI units: kelvin

Remarks:

kilogram

Definition: The base unit of mass in the SI system of units.

The ISO definition is: "The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram." (1901)

Related terms: none

Symbol: kg

SI units: kilograms = newton × seconds² / meter

Remarks:

1 kilogram = 5.609 586 2 × 10²⁹ MeV / c²

kinematic viscosity

Category: property

Definition: The ratio of the viscosity of a fluid to the density of the fluid.

Related terms: none

Symbol: ν

SI units: meters² / second

Remarks:

kinematics

Category: branch of physics

Definition: That branch of mechanics that deals with the motion of a system of objects without reference to mass or force.

Related terms: dynamics

Symbol: not applicable

SI units: not applicable

Remarks:

Kinematics is considered to be a branch of mechanics despite the fact that mechanics is defined as being concerned with forces.

kinetic

Category: concept

Definition: Of, or related to, the motion of objects and the forces and energies associated therewith.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

kinetic energy

Category: scalar quantity

Definition: The work required to bring a object in motion in an inertial reference frame to rest in the inertial reference frame.

Related terms:

For a list of other related terms see: energy

Symbol: T

SI units: joules = newton × meters

Remarks:

The motion can be either rectilinear motion or rotational motion.

The kinetic energy of a object due to linear motion is:

K = mc²(γ-1)

where:

m = rest mass

Newton's law of universal gravitation

At nonrelativistic velocities, the above equation reduces (via a binomial expansion of the square root) to:

K = (1/2)mv²

The kinetic energy of a object due to its rotational motion is:

K = (1/2)Iω²

where:

I = moment of inertia

ω = angular velocity

kinetic theory

Category: theory

Definition: A theory that combined the following concepts:

atomic theory of matter
internal energy
heat

SI units: not applicable

Remarks:

The mathematical expression of Lagrange's equations of motion is:

(i = 1, 2, 3, ...)

where:

t = time

L = Lagrangian = T-U

T = kinetic energy

U = potential energy

q_i = generalized coordinate

Lagrangian function
Lagrangian

Category: mathematical expression

Definition: A mathematical expression for the kinetic energy minus the potential energy in a conservative system.

Symbol: L

SI units: not applicable

Remarks:

The mathematical expression of the Lagrangian is:

L = T(q_i,_i) - U(q_i,_i)

where:

L = Lagrangian

T = kinetic energy

U = potential energy

q_i = generalized coordinate

_i = generalized acceleration

laminar flow
viscous flow
streamline flow

Category: phenomenon

Definition: Steady flow of a fluid in which the fluid moves in parallel layers.

Related terms: turbulent flow

Symbol: not applicable

SI units: not applicable

Remarks:

Laplace's equation

Category: mathematical expression

Statement: An equation that states that the Laplacian of a mathematical function is zero.

Ñ²V = 0

Related terms: Poisson's equation

Symbol: not applicable

SI units: not applicable

Remarks:

Laplacian

Category: operator

Definition: The three-dimensional second-order partial differential operator.

Related terms: none

Symbol: Ñ²

SI units: not applicable

Remarks:

In Cartesian coordinates, the Laplacian of the mathematical function f is equivalent to:

latent heat

Category: scalar quantity

Definition: The quantity of heat absorbed or released in an isothermal change of phase.

Related terms: none

Symbol: L

SI units: joules = newton × meters

Remarks:

law

Category: generic term

Definition: A scientific proposition that, insofar as is known, is true and invariable under the specified conditions.

Related terms:

For a list of other related terms see: proposition

Symbol: not applicable

SI units: not applicable

Remarks:

Frequently, the conditions are not explicitly stated and may not even be accurately known.

Examples:

Le Chatelier's principle

Category: principle

Statement: When a constraint is applied to a dynamic system in equilibrium, changes takes place within the system, opposing the constraint and tending to restore equilibrium.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

least action principle
least action

Category: principle

Statement: The trajectory of a system is that path that makes the action stationary relative to nearby values between the same configurations and for which the energy has the same constant value.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

least time principle
principle of least time
Fermat's principle
least time

Category: principle

Statement: The path of a ray between two points during reflection or refraction is the path of least time.

Related terms: stationary time principle

Symbol: not applicable

SI units: not applicable

Remarks:

left-hand rule
left-handed

Category: concept

Statement:

Hold the fingers of the left-hand in the plane of rotation.
Bend the fingers in the direction of rotation.
The thumb then points in the positive direction.

Steps 2 and 3 may be reversed depending on what is known.

Related terms: none

Symbol: L

SI units: not applicable

Remarks:

If the above rule does not hold then the system is right-handed

Legendre polynomial
Legendre function

Category: mathematical expression

Definition: A solution to Legendre's equation.

Related terms: none

Symbol: P_n(x)

SI units: not applicable

Remarks:

Legendre polynomials arise when studying physical phenomena having spherical geometry and in many other applications.

The mathematical expression for Legendre polynomials is:

The first three Legendre polynomials are:

P₀(x) = 1

P₁(x) = x

P₂(x) = ½(3x²-1)

...

Legendre's equation

Category: mathematical expression

Definition: A differential equation of the form:

where:

l is a constant

Related terms: Legendre polynomials

Symbol: not applicable

SI units: not applicable

Remarks:

length

Category: base quantity

Definition: One of those fundamental quantities that can not be defined except in terms of other fundamental quantities. These are: force, length, mass, and time.

Related terms: base quantities, relativity

Symbol: varies

SI units: meters

Remarks:

Length is a base quantity in the SI system of units.

Lenz's law

Category: law

Statement: An induced emf always gives rise to an electric current whose magnetic field opposes the change that produced it.

Related terms: none

For a list of other related terms see: electric induction

Symbol: not applicable

SI units: not applicable

Remarks:

lepton
normal lepton
antilepton

Category: category of particle

Definition: Lepton is a generic term for all elementary particles that have spin 1/2 and do not take part in strong interactions.

A normal lepton is a normal particle.

An antilepton is the antimatter equivalent of a normal lepton.

Related terms:

generation	charged leptons	neutrinos	charged antileptons	antineutrinos
electric charge	-1	0	+1	0
lepton number	+1	0	-1	0
1st	electron	electron neutrino	positron	electron antineutrino
2nd	muon	muon neutrino	antimuon	muon antineutrino
3rd	tauon	tauon neutrino	antitauon	tauon antineutrino

For a list of other related terms see: particle categories

Symbol: not applicable

SI units: not applicable

Remarks:

There are three principal categories of elementary particles:

leptons
quarks
gauge bosons

There are exactly 3 × 2 × 2 = 12 leptons in total.

Each generation of lepton has a distinct quantized property the value of which is given by a quantum number called a lepton number.

All charged leptons and are identical except for: electric charge, mass, and lepton number

lepton number
lepton quantum number

Category: quantum number

Definition: An additive quantum number associated with a quantized property of each of the leptons. Also the property itself.

Related terms:

For a list of other related terms see: quantum number

Symbol: l

Values: -1, 0, or +1

Remarks:

Each generation of lepton has a distinct type of lepton number:

generation	name	normal leptons	antileptons
1st	electron lepton number	+1	-1
2nd	muon lepton number	+1	-1
3rd	tauon lepton number	+1	-1

All other elementary particles have lepton numbers of 0.

The total of each type of lepton number is conserved in all particle interactions.

light
visible spectrum

Category: phenomenon

Definition: That range of electromagnetic radiation that is detectable by the human eye.

Related terms: electromagnetic wave

Symbol: not applicable

SI units: not applicable

Remarks:

The frequency range of electromagnetic radiation that can be detected by the human eye is approximately 400 tera hertz to 750 tera hertz.

The term light is sometimes loosely used in place of electromagnetic radiation of any frequency.

light travel time

Category: scalar quantity

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: seconds

Remarks:

light-year

Definition: The distance that electromagnetic radiation travels in a vacuum in one year.

Related terms: speed of light

Symbol: ??

Values: 1 light-year = 9.460528 × 10¹² meters

Remarks:

line
curve

Category: geometric element

Definition: A straight or curved geometric element such as is generated by a moving point and that has extension only along the path of the point.

Related terms: surface, space

Symbol: not applicable

SI units: not applicable

Remarks:

line current

Category: vector quantity

Definition: An electric current along a line.

Related terms: surface current, volume current

For a list of other related terms see: electric current

Symbol: I

SI units: amperes = coulombs / second

Remarks:

Line current is the relevant quantity when a electric current flows along a line as opposed to over a surface (surface current density), or through a volume (volume current density).

Much of the time only the magnitude of a line current is of interest and line current is treated as a scalar.

linear

Category: common term

Definition: Directly proportional.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

A mathematical function (y) of the variable (x) is linear with respect to the variable (x) if:

1) f(x₁+x₂) = f(x₁)+f(x₂)

and

2) f(ax) = af(x)

linear homogeneous differential equation

Category: mathematical expression

Definition: An ordinary differential equation of the form:

a₀y + a₁dy / dx + a₂d²y / dx² + ... = 0

where:

y = mathematical function of x

a_n = constant of mathematical function of x

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The equation is called linear because it does not contain any products of y and derivatives of y such as y², y(dy / dx), (dy / dx)², etc.

The equation is called homogeneous because every term contains y or a derivative of y; i.e. there is no term that is a constant or a mathematical function of x alone.

linear strain
longitudinal strain

Category: scalar quantity

Definition: The change in length per unit of length when a object is subjected to a compressive stress or a tensile stress.

Related terms: Young's modulus

For a list of other related terms see: stress

Symbol: ε

SI units: dimensionless

Remarks:

lines of force

Category: notational convention

Definition: Lines drawn in order to visualize a force field. The direction of the lines at every point are drawn so as to indicate the direction of the force on a test charge.

Related terms:

For a list of other related terms see: force

Symbol: not applicable

SI units: not applicable

Remarks:

liquid

Category: substance

Definition: A phase of matter, intermediate between a gas and a solid, that is characterized by ability to flow and near incompressibility.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

liter

Definition: A unit of measurement of volume.

Related terms: none

Symbol: L

SI units: 1 liter = 1 cubic deci meter = 10^-3 meter³

Remarks:

Use of the term liter is discouraged when giving the results of high accuracy measurements.

lithium

Category: chemical element

Definition: The chemical element having atomic number 3.

Related terms: hydrogen, helium

Symbol: Li

SI units: not applicable

Remarks:

Lobachevskian geometry
hyperbolic geometry

Category: branch of mathematics

Definition: A non-Euclidean geometry in which the parallel postulate of Euclidean geometry is replaced by the postulate that through any point not on a given straight line, there are an infinite number of straight lines that are parallel to the given line.

The following possess locality:

particles

The following do not possess locality:

space
time

longitudinal wave
pressure wave
P-wave

Category: concept

Definition: A wave in which the displacement of the transmitting medium is parallel to the direction of propagation.

Related terms: transverse wave

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

Sound

Lorentz factor

Category: number

Definition: A factor in the Lorentz transformation equations.

Related terms: none

Symbol: γ

SI units: dimensionless

Remarks:

The mathematical expression of the Lorentz factor is:

where:

u = velocity as measured in the lab frame

The Lorentz factor is defined for convenience in notation.

Lorentz force

Category: vector quantity

Definition: The total force on an electric charge that is moving in coincident electric field and magnetic field.

Related terms: Lorentz force law

Symbol: varies

SI units: newtons

Remarks:

Lorentz force law

Category: law

Statement: The total force on an electric charge in motion in coincident electric field and magnetic fields is the vector sum of the electric force and the magnetic force acting on the electric charge.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of the Lorentz force law is:

F = q [ E + (v ´ B) ]

where:

F = Lorentz force

q = amount of electric charge

v = velocity of the electric charge

The velocity must be measured with respect to the inertial reference frame in which the magnetic force is zero.

Lorentz transformation

Category: mathematical operation

Definition: The mathematical transformation of coordinates from one inertial reference frame to another taking into account relativistic effects.

Related terms: Lorentz transformation equations

Symbol: not applicable

SI units: not applicable

Remarks:

Lorentz transformation equations

Category: mathematical operation

Definition: The set of equations that transform the coordinates of an event in one inertial reference frame to the coordinates of the event in a second inertial reference frame that is in motion with respect to the first reference frame.

Related terms: Galilean transformation equations

Symbol: not applicable

SI units: not applicable

Remarks:

There are similar equations for transforming motion-related quantities, such as velocity, momentum, and kinetic energy, from the lab frame to a moving frame.

In the simple case of two inertial reference frames with similarly oriented Cartesian coordinate systems moving along their common x axes, the equations for the Lorentz transformation are:

Dx' = γ(Dx-v(Dt)]

Dy' = Dy

Dz' = Dz

Dt' = γ[Dt-(v / c²)Dx]

where:

primed coordinates are in the moving frame

unprimed coordinates are in the lab frame

v = the speed of the moving frame relative to the lab frame

lumen

Definition: The unit of measurement of luminous flux in the SI system of units.

Related terms: none

Symbol: lm

SI units: 1 lumen = 1 candela × steradian

Remarks:

luminance

Category: vector quantity

Definition: The luminous intensity per unit of projected area of a point source of light.

Related terms: illuminance, radiance

Symbol: L

SI units: candela / meter²

Remarks:

luminosity

Category: property

Definition: The attribute of a source of light that gives the visual sensation of brightness.

Related terms: none

Symbol: ??

SI units: ??

Remarks:

The luminosity of a source of light depends on the radiant flux, but also on the fact that the sensitivity of the eye varies for different wavelengths.

luminous flux

Category: scalar quantity

Definition: The time rate of flow of electromagnetic radiation evaluated according to its capacity to produce a visual sensation in the human eye.

Related terms: none

Symbol: F

SI units: lumens = candela × steradian

Remarks:

luminous intensity
candle power

Category: base quantity

Definition: The luminous flux emitted per unit of solid angle by a point source in a given direction.

Related terms: base quantities

Symbol: I

SI units: candela = lumens / steradian

Remarks:

Luminous intensity is a base quantity in the SI system of units.

The use of the term candle power is discouraged.

lux

Definition: The unit of measurement of illuminance in the SI system of units.

Related terms: none

Symbol: lx

SI units: 1 lux = 1 lumen / meter² = 1 candela × steradian / meter²

Remarks:

Lyman series
Balmer series
Paschen series
Brackett series
Pfund series

Category: phenomenon

Definition: A series of lines in the hydrogen spectrum that are represented by the mathematical expression:

1/λ = R(1/n₁² - 1/n₂²)

where:

λ = wavelength of a line in the series

R = Rydberg constant

n₁ = an integer

n₁	series
1	Lyman
2	Balmer
3	Paschen
4	Brackett
5	Pfund

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

magnetic

Category: concept

Definition: Of, related to, or characterized by magnetism.

Related terms: electromagnetism

For a list of other related terms see: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

magnetic charge

Category: scalar quantity

Definition: (to be completed at a later time)

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: ??

SI units: ??

Remarks:

magnetic circuit

Category: concept

Definition: The completely closed path described by a magnetic line of force.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

magnetic dipole

Category: concept

Definition: If an electric circuit exists in a magnetic field, it will experience a torque. In this circumstance, the electric circuit is called a magnetic dipole, and the torque is called the magnetic dipole moment.

Related terms: electric dipole, magnetic dipole moment

For a list of other related terms see: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

Magnetic dipole originally referred to magnets, but magnets are formed by the alignment of the motion of the electrons in the atoms forming the magnet. Therefore a magnet is just a macroscopic magnetic dipole.

magnetic energy

Category: scalar quantity

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: joules = newton × meters

Remarks:

magnetic field
B field

Category: phenomenon

Definition: A force field produced by a magnetic pole, an electric charge in motion, an electric current, or a varying electric field.

Related terms: field, magnetism

For a list of other related terms see: electricity and magnetism, field

Symbol: not applicable

SI units: not applicable

Remarks:

The term magnetic field is often used when magnetic flux density is the intended meaning.

magnetic field strength (H)
magnetic field intensity
magnetic intensity
magnetizing force
H field

Category: vector quantity

Definition: The ratio of the magnetic flux density at a given point to the permeability of the local medium.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: H

SI units: amperes / meter = coulombs / meter × second

Remarks:

The magnetic field strength created by a long straight wire carrying a electric current is:

H = (I / 2πr) i^

where:

I = electric current

r = distance from wire

i^ unit vector in the direction of the electric current

Magnetic field strength (H) is related to magnetic flux density (B) by the following mathematical expression:

H = B / μ

where:

μ = permeability of the medium

magnetic field vector

Related terms:

For a list of other related terms see: electricity and magnetism

Definition: (to be completed at a later time)

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: ??

SI units: not applicable

Remarks:

magnetic flux (F)
magnetic field flux
flux of magnetic induction

Definition: This is a toughie!

Category: scalar quantity

Related terms: magnetic field, magnetic flux density

For a list of other related terms see: electricity and magnetism

Symbol: F

SI units: webers = joules / ampere = newton × meter × seconds / coulomb

Remarks:

dF = B • da

where:

F = magnetic flux

a = area

magnetic flux density (B)
magnetic induction

Category: vector quantity

Definition: Magnetic flux per unit of area.

For a list of other related terms see: electricity and magnetism

Symbol: B

SI units: teslas = webers / meter² = newton × seconds / coulomb × meter

Remarks:

In a vacuum, magnetic flux density is related to magnetic field strength by the following mathematical expression:

B = μ₀H

where:

magnetic force

Category: vector quantity

Definition: The force exerted on an electric charge by a magnetic field.

Related terms:

For a list of other related terms see: force

Symbol: varies

SI units: newtons

Remarks:

magnetic force law

Category: law

Statement: The magnetic force on an electric charge moving in a magnetic field is equal to the product of the magnitude of the electric charge and the cross product of the velocity of the electric charge and the magnetic flux density.

Related terms: Lorentz force law

For a list of other related terms see: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of the magnetic force law is:

F = Q(v ´ B)

where:

F = magnetic force

Q = magnitude of the electric charge

v = velocity of the electric charge

The direction of the magnetic force is at right angles to both the velocity and the magnetic field and is determined by the right-hand rule.

The velocity must be measured with respect to the inertial reference frame in which the magnetic force is zero.

Like Coulomb's law, the magnetic force law is based on empirical evidence (i.e. it is not derived from other considerations).

magnetic inductance

Category: ??

Definition: This term is not used.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

magnetic moment
magnetic dipole moment
electromagnetic moment

Category: vector quantity

Definition: The torque experienced by an electric circuit in a magnetic field.

Of an electrically charged particle with spin, ??

For a list of other related terms see: electricity and magnetism

Symbol: m

SI units: ampere × meters² = coulomb × meters / second

Remarks:

The mathematical expression for the torque is:

L = m ´ B

newton × meters = (coulomb × meters² / second) × (newton × seconds / coulomb × meter)

where:

L = torque

m = magnetic dipole moment

Alternatively, magnetic moment is sometimes defined as the ratio of the torque to the magnetic field strength in which case, the mathematical expression for the torque is:

L = m ´ H

where:

L = torque

m = magnetic moment (weber × meter)

Magnetic dipole moment is used as a measure of magnetic field strength.

magnetic monopole

Category: hypothetical particle

Definition: A hypothetical particle with a magnetic charge of either north or south.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: ??

SI units: not applicable

Remarks:

The existence of magnetic monopoles is predicted by several theories but, as of June 2001, none have been observed.

magnetic pole

Category: phenomenon

Definition: A region in a magnetized object in which the magnetic flux density is more or less concentrated.

Related terms: magnetic monopole

For a list of other related terms see: electricity and magnetism

Symbol: ??

SI units: not applicable

Remarks:

magnetic potential
magnetic potential energy

Category: scalar quantity

Definition: The potential energy of an electrically charged object in a magnetic field.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: ??

SI units: joules = newton × meters

Remarks:

The magnetic potential per unit volume of a magnetic field is:

Energy = μH²/2

where:

μ = permeability in the medium

H = magnitude of the magnetic field strength

magnetic potential difference

Category: scalar quantity

Definition: The difference between the magnetic states of two points in a magnetic field.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: ΔU

SI units: ??

Remarks:

When electric currents are present, the concept of magnetic potential difference is not valid.

magnetic quantum number

Category: quantum number

Definition: (to be completed at a later time)

Category: phenomenon

Definition: A complex phenomenon associated with the motion of electric charges.

Related terms: electromagnetism

For a list of other related terms see: electricity and magnetism

Symbol: not applicable

SI units: not applicable

Remarks:

magnetization

Category: scalar quantity

Definition: The magnetic moment of a object, per unit of volume.

Related terms: electric polarization

Symbol: M

SI units: webers / meter² = newton × seconds / coulomb × meter

Remarks:

Magnetization is caused by electric currents or by elementary atomic magnetic moments.

magnetized

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

magnetomotive force

Category: scalar quantity

Definition: The integral the magnetic field strength around a closed path.

Related terms:

For a list of other related terms see: force

Symbol: F_m

SI units: amperes = coulombs / second

Remarks:

magneton

Category: property

Definition: The intrinsic magnetic moment of a particle.

Related terms: Bohr magneton, nuclear magneton

Symbol: μ

SI units: joules / tesla = coulomb × meters² / second

Remarks:

magnetostatic field

Category: field

Definition: (to be completed at a later time)

Related terms:

For a list of other related terms see: field

Symbol: not applicable

SI units: not applicable

Remarks:

magnetostatic potential

Category: scalar quantity

Definition: (to be completed at a later time)

Related terms: potential

Symbol: ??

SI units: ??

Remarks:

magnetostatics

Category: branch of physics

Definition: That branch of physics that deals with magnetic fields produced by steady electric currents.

Related terms:

For a list of other related terms see: dynamics

Symbol: not applicable

SI units: not applicable

Remarks:

The magnetic fields produced by magnets are due to the steady motion of electrons in the atoms of the magnet and therefore magnetostatics includes the study of magnets.

The study of magnetic fields produced by varying electric currents is included within electrodynamics.

magnitude
size

Category: concept

Definition:

Of a scalar quantity, the numerical value.
Of a vector quantity, the numerical value disregarding the direction.

Related terms: amount, extent

Symbol: ??

SI units: not applicable

Remarks:

main diagonal

Category: mathematical expression

Definition: The elements of a square matrix from the upper left corner to the lower right corner.

Related terms: matrix, unit matrix

Symbol: not applicable

SI units: not applicable

Remarks:

manifold

Category: concept

Definition: A topological space such that every point in the topological space has a neighborhood that is homeomorphic to the interior of a sphere in Euclidean space of the same number of dimensions.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

mass

Category: base quantity

Definition: One of those fundamental quantities that can not be defined except in terms of other fundamental quantities. These are: force, length, mass, and time.

Mass is the charge that produces the gravitational force.

Symbol: m

SI units: kilograms

Remarks:

Mass is a base quantity in the SI system of units.

Inertial mass is that property of a object by which the object has inertia.

Gravitational mass is that property of a object by which the object produces a gravitational field.

As far as we know, inertial mass is the selfsame property as gravitational mass.

massive
massless

Category: concept

Definition:

Massive means having a nonzero mass.
Massless means having a zero mass.

Symbol: not applicable

SI units: not applicable

Remarks:

In common usage massive implies a very large mass, this may be the case but not necessarily so when speaking of particles.

mathematical equation

Category: mathematical expression

Definition: A mathematical expression that asserts that one mathematical expression is equal to another mathematical expression.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

mathematical expression
expression
formula

Category: concept

Definition: A mathematically valid combination of operators and operands.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The operands may be constants or variables.

mathematical function
function

Category: generic term

Definition: A mathematical expression that assigns exactly one element of one set to each element of the same or another set.

Related terms: trigonometric functions

Symbol: f(x)

SI units: not applicable

Remarks:

mathematical group

Category: concept

Definition: A group of elements or mathematical operations (a, b, c, ...) for which a law of combination may be defined so that the product (ab) of any two elements is well defined and satisfies the following conditions:

If a and b belong to the set, so does ab.
Combination is associative; that is a(bc) = (ab)c.
The set contains an element (e), called the identity, such that ae = ea = a for all elements (a) of the set.
For every element (a) in the set, there is an element (b) such that ab = ba = e.

Related terms: group theory

Symbol: varies

SI units: not applicable

Remarks:

mathematical operand
operand

Category: mathematical expression

Definition: A number or a symbol representing a number or quantity in a mathematical expression that is operated on by a mathematical operator.

Related terms: mathematical operator

Symbol: not applicable

SI units: not applicable

Remarks:

mathematical operation
operation

Category: concept

Definition: A process of deriving one mathematical expression from another according to a rule.

Related terms: mathematics

Symbol: not applicable

SI units: not applicable

Remarks:

mathematical operator
operator

Category: mathematical expression

Definition: A mathematical expression or symbol denoting an mathematical operation to be performed.

Related terms: mathematical operand

Symbol: varies

SI units: not applicable

Remarks:

Examples:

operator	meaning
+	plus
-	minus
d	total differential
¶	partial differential
•	dot product
´	cross product

mathematical transformation
transformation

Category: mathematical operation

Definition: A mathematical operation that changes one mathematical expression into another equivalent mathematical expression in accordance with a set of rules.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Some specific mathematical transformations are:

Lorentz transformation

space inversion

mathematics

Category: branch of science

Definition: The study of numbers and their operations, interrelations, combinations, generalizations, and abstractions, and of space configurations and their structure, measurement, transformations, and generalizations.

Symbol: not applicable

SI units: not applicable

Remarks:

matrix

Category: mathematical expression

Definition: A rectangular array of mathematical elements.

Related terms: none

Symbol: an array in brackets

SI units: not applicable

Remarks:

An matrix of order m x n is an array of m rows and n columns of numbers.

The individual numbers are called elements of the matrix.

matrix mechanics

Category: theory

Definition: One of the mathematical expressions of quantum mechanics.

Related terms:

For a list of other related terms see: quantum mechanics

Symbol: not applicable

SI units: not applicable

Remarks:

Matrix mechanics is equivalent to wave mechanics. In matrix mechanics, the wave functions of wave mechanics are replaced by vectors in a Hilbert space and physical quantities are represented by time-dependent matrices.

Matrix mechanics is not useful for obtaining quantitative solutions to actual problems but, because it is concisely expressed in a form independent of special coordinate systems, it is useful for proving general theorems.

Matrix mechanics was developed by Bohr and Heisenberg.

matter

Category: phenomenon

Definition: Any object, particle, or substance that has primarily particle-like properties as opposed to wave-like properties.

Depending upon the context, any of the following may be intended:

ordinary matter only
normal matter only
normal matter and antimatter.

Related terms:

For a list of other related terms see: object, particle categories

Symbol: not applicable

SI units: not applicable

Remarks:

The following are matter: atoms, leptons, quarks.

The following are NOT matter: force fields, gluons, photons

Usually matter is thought of as occupying space and having mass. However, electrons are thought to be point particles and neutrinos may not have mass. Nevertheless, electrons and neutrinos are considered to be matter.

Matter is convertible in to energy.

Maxwell's equations
Maxwell's electromagnetic theory

Category: theory

Definition: A set of four equations that describe electric and magnetic phenomena.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of Maxwell's equations is:

Ñ • E = ρ / ε₀ (Gauss's law)

Ñ ´ E = - ¶B / ¶t (Faraday's law)

Ñ • B = 0 (no name)

Ñ ´ B = μ₀J + μ₀ ε₀ ¶E / ¶t (Ampere's law)

Maxwell's equations, together with the Lorentz force law, provide a complete definition of the phenomena of electricity and magnetism:

Ampere's law is stated here in a form that was modified by Maxwell to take into account varying electric field strengths.

Maxwell-Boltzmann statistics

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

mean decay time

Category: scalar quantity

Definition: (to be completed at a later time)

Related terms:

For a list of other related terms see: decay

Symbol: ??

SI units: seconds

Remarks:

Mean decay times for types of interactions are:

interaction	mean decay time, seconds
strong interaction	10^-23
electromagnetic interaction	10^-16
weak interaction	??

mean free path

Category: scalar quantity

Definition: The arithmetic mean distance that a particle travels between two successive interactions.

Related terms: none

Symbol: λ

SI units: meters

Remarks:

mean lifetime
lifetime

Category: scalar quantity

Definition: The mean time for which an particle exists before it decays.

Definition: The arithmetic mean of the lifetimes of a population.

Related terms: half-life

For a list of other related terms see: decay

Symbol: τ

SI units: seconds

Remarks:

The mean lifetime is the reciprocal of the decay constant.

The mean lifetime is related to the half-life by the mathematical expression:

t_½ = (ln 2) × τ » 0.693 × τ

For exponential decay, mean lifetime is equal to the reciprocal of the decay constant:

τ = 1 / λ

where:

τ = mean lifetime

λ = decay constant

measurement

Category: common term

Definition: A number, extent, or amount obtained by physical comparison to a standard quantity.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

mechanical

Category: concept

Definition: Pertaining to the quantitative relations of forces and matter.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

mechanical energy
total mechanical energy

Category: scalar quantity

Definition: The sum of the kinetic energy and the potential energy of a system.

Related terms:

For a list of other related terms see: energy

Symbol: ??

SI units: joules = newton × meters

Remarks:

Note that mechanical energy does not include internal energy.

mechanical impedance

Category: scalar quantity

Definition: The complex ratio of the force acting in the direction of motion to the velocity.

Symbol: Z_m

SI units: newton × seconds / meter

Remarks:

The mathematical expression for mechanical impedance is:

Z_m = F / v

where:

Z_m = mechanical impedance

F = driving force

v = velocity

Mechanical impedance is a function of mechanical resistance and mechanical reactance.

Z_m = (R_m² + X_m²)^½

where:

Z_m = mechanical impedance

R_m = mechanical resistance

X_m = mechanical reactance

mechanical reactance

Category: scalar quantity

Definition: The imaginary part of mechanical impedance.

Related terms: none

Symbol: X_m

SI units: newton × seconds / meter

Remarks:

mechanical resistance

Category: scalar quantity

Definition: The real part of mechanical impedance.

Related terms: impedance, resistance

Symbol: R_m

SI units: not applicable

Remarks:

mechanics

Category: branch of physics

Definition: That branch of physics that deals with the behavior of a system of objects when they are subjected to forces.

Related terms: see remarks

Symbol: not applicable

SI units: not applicable

Remarks:

Mechanics is concerned with energy, force, inertia, mass, momentum, and motion.

Mechanics can be divided in several ways.

Based on motion:

dynamics
kinematics
statics

Based on size of the system:

classical mechanics
nonrelativistic quantum mechanics

Based on velocity

nonrelativistic mechanics
relativistic mechanics

Other bases:

continuum mechanics
statistical mechanics
fluid mechanics
celestial mechanics

median
central value

Definition: The central value in a set of values arranged in order of magnitude.

Related terms:

For a list of other related terms see: arithmetic mean

Symbol: ??

SI units: not applicable

Remarks:

The number of values less than the median is equal to the number of values greater than the median.

mediate

Category: concept

Definition: To transmit as an intermediate mechanism or agency.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

medium

Category: substance

Definition: A substance regarded as the means of transmission of a force, quantity, or effect.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

meson

Category: category of particle

Definition: A generic term for all particles that are composed of quark - antiquark pairs.

Related terms:

For a list of other related terms see: particle categories

Symbol: varies

SI units: not applicable

Remarks:

All mesons have integer spin and are therefore bosons.

All mesons are composed of quarks and are therefore hadrons:

A meson is its own antiparticle.

metaphysics

Category: philosophical term

Definition: A branch of philosophy that includes:

Cosmology, the study of the origin, evolution, structure, composition, and nature of the universe as a whole,
Epistemology, the study of the nature and grounds of knowledge especially with reference to its limits and validity, and
Ontology, the study of the nature of being.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

metastable

Category: phenomenon

Definition: A state of pseudo-equilibrium.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

meter

Definition: The base unit of length in the SI system of units.

The ISO definition is: "The meter is the length of the path traveled by light in vacuum during a time interval of 1/299 792 458 of a second." (1983)

Related terms: foot

Symbol: m

SI units: meters

Remarks:

metric

Category: concept

Definition: Of, or relating to, a metric system of units.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

metric system of units
metric system

Category: system of units

Definition: Any of the following systems of units:

cgs system of units
MKS system of units
SI system of units

Related terms:

For a list of other related terms see: systems of units

Symbol: not applicable

SI units: not applicable

Remarks:

MeV

Definition: One million electronvolts.

Related terms: none

Symbol: MeV

Values: 1 MeV = 10⁶ electronvolts = 1.602 177 33 × 10^-13 joules (newton × meters)

Remarks:

1 MeV/c² = 0.178 266 27 × 10^-29 kilograms

micro meter
micron

Definition: One millionth of a meter.

Related terms: SI prefixes

Symbol: μm

Values: 1 micrometer = 10^-6 meter

Remarks:

microscopic

Category: concept

Definition: A range of size at which the characteristics of individual particles are significant or dominate.

Related terms: macroscopic

Symbol: not applicable

SI units: not applicable

Remarks:

Quantum theory, for example, is typically an analysis of behavior on a microscopic scale.

microwave

Category: quality

Definition: Electromagnetic radiation with a wavelength in the approximate range 0.001 meter to 0.1 meter.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Minkowski geometry

Category: branch of physics

Definition: The geometry of Minkowski space-time.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

An event in Euclidean space-time corresponds to a (world) point in Minkowski space-time.

A point in Euclidean space-time corresponds to a (world) line in Minkowski space-time.

Definition: If f(x) is a frequency distribution giving the frequency or probability of x, then the mode of x is the value of x for which f(x) is a maximum.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

model

Category: generic term

Definition: A scientific proposition expressed in terms of phenomena we are familiar with.

Related terms:

For a list of other related terms see: proposition

Symbol: not applicable

SI units: not applicable

Remarks:

Often the model will attempt to provide a mental image of the phenomenon.

modern physics

Category: branch of physics

Definition: Those branches of physics that have developed from about 1905 to the present. It encompasses quantum mechanics, relativity, and cosmology.

Related terms: classical physics

Symbol: not applicable

SI units: not applicable

Remarks:

Modern physics includes, in particular, the relativity and quantum theories.

modulus

Category: mathematical expression

Definition: A constant or coefficient that expresses the degree to which a object or substance possesses a property.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

modulus of elasticity
elastic modulus

Category: scalar quantity

Definition: The ratio of stress to strain in a object that is subjected to stress.

A modulus of elasticity will be constant (i.e. Hooke's law applies) only over a limited range of stress.

Outside the range (if any) of stress in which Hooke's law applies, the modulus must be defined as the ratio of a small change in stress to a small change in strain at a particular value of stress.

Related terms: bulk modulus, shear modulus, Young's modulus

For a list of other related terms see: stress

Symbol: E

SI units: pascals = newtons / meter²

Remarks:

There are several moduli because there are several types of stress.

molar

Category: common term

Definition: An adjective meaning per mole.

Related terms: Avogadro's number, mole

Symbol: not applicable

SI units: not applicable

Remarks:

molar gas constant
gas constant
universal gas constant

Category: fundamental constant

Definition: The constant in the equation of state for an ideal gas.

Related terms: none

Symbol: R

Values: 8.314 510 joules / mole × kelvin

Remarks:

molar volume

Category: fundamental constant

Definition: The volume that one mole of an ideal gas occupies at standard temperature and standard pressure.

Related terms: Avogadro constant

Symbol: V_m

Values: 1 molar volume = 22.414 liters = 22.414 × 10^-3 meters³ / mole

Remarks:

mole
gram mole

Definition: The base unit of amount of substance in the SI system of units.

The ISO definition is: "The mole is the amount of substance of a system that contains as many elementary entities as there are atoms in 0.012 kilograms of carbon 12." (1971)

Related terms: Avogadro constant, molar

For a list of other related terms see: relative atomic mass

Symbol: mol

SI units: moles

Remarks:

In the SI system of units, 1 mole of carbon-12 has a mass of 12 grams.

In the fps system of units, 1 mole of carbon-12 is understood to mean 12 pounds.

molecular weight

Category: scalar quantity

Definition: The average mass of a molecule of a chemical compound in atomic mass units.

Related terms:

For a list of other related terms see: relative atomic mass

Symbol: ??

SI units: atomic mass units

Remarks:

It is necessary to say "average" because of the existence of isotopes of the constituent elements. The isotopes of an element have different atomic masses,

molecule

Category: object

Definition: The smallest particle of a chemical compound that retains the chemical properties of the compound.

Related terms:

For a list of other related terms see: atom

Symbol: not applicable

SI units: not applicable

Remarks:

A molecule consists of atoms.

moment

Category: varies

Definition: The tendency or measure of the tendency to produce revolution about a point or axis.

See a particular term:

moment of a vector about a point
moment of a vector about an axis

Symbol: not applicable

SI units: not applicable

Remarks:

moment of a force about an axis
torque

Category: scalar quantity

Definition: See moment of a vector about an axis.

Related terms: axis, force, moment

Symbol: T

SI units: newton × meters

Remarks:

It is usually assumed that:

1) the vector lies in a plane perpendicular to the axis and

2) the intended result is the moment about the point of intersection of the plane and the axis. If this is not the case, see moment of a vector about a point.

Under the above assumptions, the mathematical expression for torque is:

T = r ´ F

where:

T = torque

r = radius vector

F = force

moment of a vector about a point
moment about a point

Category: pseudovector quantity

Definition: The cross product of the given vector and the displacement vector between the given point and any point on the line of action of the given vector.

Symbol: M

SI units: newton × meters

Remarks:

The mathematical expression for moment of a vector about a point is:

M = r ´ v

where:

r = displacement vector

v = given vector

moment of a vector about an axis
moment about an axis

Category: scalar quantity

Definition: The product of the shortest distance of the line of action of the vector from the axis and the component of the vector in the plane perpendicular to the axis.

Symbol: M

SI units: newton × meters

Remarks:

The moment of a vector about an axis may also be defined as the component in the direction of the axis, of the moment of a vector about a point, the point being on the axis.

Following this latter definition, the mathematical expression for moment of a vector about an axis is:

M = n • (r ´ v)

where:

n = unit vector along the axis

r = displacement vector

v = given vector

The term moment about an axis is often used when the intended meaning is: a vector with 1) the above magnitude and 2) a direction along the axis:

M = M × n = n • (r ´ v) × n

moment of inertia
rotational inertia

Category: scalar quantity

Definition: The moment of inertia of a point mass about an axis is the product of the mass and the square of the perpendicular distance from the axis to the mass.

Related terms: angular momentum, mass, moment, revolution, rotation, torque

Symbol: I

SI units: kilogram × meters²

Remarks:

The mathematical expression for the moment of inertia of a point mass about an axis is:

I = m × r²

where:

m = mass

r = distance from mass to axis

Often the axis will be an axis through the center of mass of a object and the total moment of inertia of the object is intended.

Example:

The moment of inertia of a uniformly dense cylinder about the longitudinal axis of the cylinder is:

where:

ρ = density of cylinder

R = radius of cylinder

L = length of cylinder

momentum
linear momentum

Category: vector quantity

Definition: The linear momentum of a object is equal to the product of its mass and its velocity.

Related terms: angular momentum, Newton's first law

Symbol: p

SI units: kilogram × meters / second

Remarks:

The mathematical expression for momentum is:

p = m × v

where:

p = linear momentum

m₀ = mass of the object

v = velocity of the object

If the velocity is a significant fraction of the speed of light, relativistic effects must be taken into account and the mathematical expression for linear momentum becomes:

p = γm₀v

where:

p = linear momentum of the object in the lab frame

m₀ = rest mass of the object in the lab frame

v = velocity of the object in the lab frame

Notice that linear momentum is dependent upon the reference frame in which the velocity is measured.

If the velocity of the object is equal to the speed of light, then the rest mass must be zero and the linear momentum by the above definitions is indeterminate. In this case, the linear momentum can be obtained by eliminating the velocity from the equation for the linear momentum (p = γm₀u) and the equation for the total energy (E = γm₀c²). This results in the equation:

E² = m₀²c⁴ + p²c²

From this equation, for a rest mass of zero, the linear momentum is:

p = E / c

motion
motion-like

Category: phenomenon

Definition: If the distance between two objects varies with time, or either object is rotating, or they are revolving around a common axis, the two objects are said to be in motion with respect to each other.

Likewise, if the position of an object is changing with respect to a reference frame, then the object is in motion with respect to the reference frame.

Symbol: not applicable

SI units: not applicable

Remarks:

In order to describe the motion of an object or reference frame, an inertial reference frame must be specified.

motive force

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

moving frame
moving reference frame
moving frame of reference

Category: concept

Definition: An inertial reference frame that is in motion with respect to the lab frame.

Related terms:

For a list of other related terms see: reference frame

Symbol: not applicable

SI units: not applicable

Remarks:

muon
mu meson
normal muon
antimuon

Category: elementary particle

Definition: A muon is an elementary particle that is similar to an electron but with a mass that is 206.768 times as great.

A normal muon is a normal particle.

An antimuon is the antimatter equivalent of a muon.

The properties of an normal muon are:

property	value
electric charge	-1
rest mass	105.659 MeV / c² = 188.354 3 × 10^-30 kilogram
spin	1/2
mean lifetime	2.197 × 10^-6 seconds

Related terms: electron, tauon

For a list of other related terms see: leptons

Symbol: μ

SI units: not applicable

Remarks:

A muon is a charged lepton.

Muons belong to the second generation of leptons.

muon neutrino
muon antineutrino

Category: elementary particle

Definition: The neutrino that belongs to the second generation of leptons.

The properties of an muon neutrino are:

property	value
electric charge	0
rest mass	very small or 0
spin	1/2
mean lifetime	?? seconds

Related terms: muon

For a list of other related terms see: leptons

Symbol: ν_μ

SI units: not applicable

Remarks:

mutual inductance

Category: scalar quantity

Category: concept

Definition: The numbers 1, 2, 3, a

Related terms: integers

For a list of other related terms see: number

Symbol: n

SI units: not applicable

Remarks:

The natural numbers are a subset of the integers.

natural units

Category: system of units

Definition: A system of units in which mass, length, and time are given the dimensions of power or energy, usually expressed in electronvolts, with the result that the Planck constant and the speed of light have a value of 1.

Related terms: Gaussian system of units

Symbol: not applicable

SI units: not applicable

Remarks:

nebula

Category: object

Definition: An extraterrestrial cloud of gas or dust.

Related terms:

For a list of other related terms see: extraterrestrial objects

Symbol: not applicable

SI units: not applicable

Remarks:

The term nebula has been used at one time or another to describe almost every kind of extraterrestrial object.

negative
negative number

Category: concept

Definition:

A number that is less than zero and opposite in sign to a positive number.
Extending or generated in a direction opposite to an arbitrarily chosen direction.
Being, related to, or charged with electricity of which the electron is the elementary unit of measurement.

Related terms: positive

Symbol: (-)

SI units: not applicable

Remarks:

negative electric charge
negative charge

Category: property

Definition: An electric charge having the same polarity as the electric charge of an electron.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: ??

SI units: not applicable

Remarks:

net force
unbalanced force

Category: vector quantity

Definition: The vector sum of all forces acting on a object.

Related terms:

For a list of other related terms see: force

Symbol: ??

SI units: newtons

Remarks:

neutral

Category: property

Definition: Having no net electric charge.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

neutrino
normal neutrino
antineutrino

Category: category of particle

Definition: Neutrino is a generic term for all elementary particles that have spin 1/2, no electric charge, and no mass. (As of June 2001, we are not sure about the mass.)

A normal neutrino is a normal particle.

An antineutrino is the antimatter equivalent of a normal neutrino.

Related terms:

For a list of other related terms see: leptons

Symbol: e / ν / τ

SI units: not applicable

Remarks:

The normal neutrinos are:

the electron neutrino,
the muon neutrino, and
the tauon neutrino.

The antineutrinos are:

the electron antineutrino,
the muon antineutrino, and
the tauon antineutrino.

For each normal neutrino there is a corresponding antineutrino; thus there are exactly 3*2 = 6 neutrinos in total.

All normal neutrinos have left-handed helicity.

All antineutrinos have right-handed helicity.

All normal neutrinos and antineutrinos are identical except for: lepton number, helicity, and possibly mass.

All neutrinos interact principally through the weak force and not at all through the strong force or the electromagnetic force.

neutron
normal neutron
antineutron

Category: particle

Definition: A neutron is a particle of matter that is composed of quarks and has no electric charge.

A normal neutron is a normal particle.

An antineutron is the antimatter equivalent of a normal neutron.

The properties of a neutron are:

property	value
electric charge	0
rest mass	939.57 MeV / c² = 1674.9 × 10^-30 kilograms
spin	1/2
mean lifetime	900 seconds

Related terms: electron, proton

For a list of other related terms see: particle categories

Symbol: n

SI units: not applicable

Remarks:

All neutrons interact though the strong force, weak force, and gravitational forces but not through the electromagnetic force.

A neutron has a mass roughly equal to that of a proton and about 1838.7 times that of an electron.

A neutron is a fermion (since it has spin of 1/2) and a hadron (since it takes part in strong interactions) and a baryon (since it is a fermion and a hadron).

neutron number

Category: scalar quantity

Definition: The number of neutrons in the nucleus of an atom.

Related terms: nucleon number, proton number

For a list of other related terms see: relative atomic mass

Symbol: N

SI units: dimensionless

Remarks:

newton

Definition: The unit of measurement of force in the SI system of units.

Related terms: none

Symbol: N

SI units: 1 newton = kilogram × meter / second²

Remarks:

In the SI system of units, a newton is by definition the amount of force that will accelerate a mass of one kilogram at a rate of one meter per second per second.

Newton's first law
Newton's first law of motion

Category: law

Statement: A object will remain at rest or in uniform motion unless it is acted upon by an external force.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

In order for Newton's first law to hold, the reference frame of the observer must be in uniform motion. In other words, the reference frame of the observer must be an inertial reference frame, i.e., must not be accelerating or rotating at any time during an experiment.

Newton's law of universal gravitation
universal gravitation

Category: law

Statement: Every particle of mass attracts every other particle of mass in the universe with a force that is proportional to the product of the two masses and inversely proportional to the square of the distance between them.

Related terms:

For a list of other related terms see: gravitation

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of Newton's law of universal gravitation is:

where:

F = gravitational force

m = mass of test mass

M = mass of the source mass

r = distance of separation of the masses

r^ = unit vector in direction from m to M

Newton's laws
Newton's laws of motion

Category: generic term

Definition: A set of laws concerning motion.

Newton's first law
Newton's second law
Newton's third law

Symbol: not applicable

SI units: not applicable

Remarks:

Newton's second law
Newton's second law of motion

Category: law

Statement: A object acted upon by a force moves in such a manner that the time rate of change of linear momentum equals the force.

Related terms: Newton's laws of motion

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of Newton's second law is:

F = d(mv) / dt

where:

F = force

m = mass

v = velocity

t = time

This equation defines the relationship among the four fundamental quantities: force, inertial mass, length, and time.

For constant mass, the above equation becomes:

F = m(dv/dt) = ma

where:

a = acceleration

This is one of the most famous equations in physics.

Newton's third law
Newton's third law of motion

Category: law

Statement: If two objects exert forces on each other these forces are equal in magnitude and opposite in direction.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Newtonian

Category: ??

Definition: Of, by, or in the manner of Isacc Newton.

Symbol: not applicable

SI units: not applicable

Remarks:

Newtonian fluid
non-Newtonian fluid

Category: property

Definition: For a fluid in laminar flow, if the velocity gradient is proportional to the stress, the fluid is said to be a Newtonian fluid.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Newtonian force

Category: concept

Definition: A force that follows an inverse square law.

Related terms:

For a list of other related terms see: force

Symbol: ??

SI units: newtons

Remarks:

Newtonian theory of relativity
Newtonian relativity

Category: theory

Definition: (to be completed at a later time)

Related terms:

For a list of other related terms see: relativity

Symbol: not applicable

SI units: not applicable

Remarks:

The unspoken assumptions of Newtonian theory of relativity are that time is everywhere the same and information can be propagated to any distance instantaneously.

node

Category: concept

Definition: A point in an oscillating system at which the oscillating quantity is at a minimum or zero.

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

Noether's theorem

Category: theorem

Statement: Every symmetry of nature yields a conservation law. Conversely, every conservation law reveals an underlying symmetry.

Related terms: conserved, invariant

Symbol: not applicable

SI units: not applicable

Remarks:

Symmetry is synonymous with invariance.

Invariant means unchanged by a mathematical operation.

Conserved means unchanged by a physical process.

The following are some invariances (symmetries) and their corresponding conserved quantities:

invariance	conserved quantity
translation of time	energy
translation of space	momentum
rotation of space	angular momentum
inversion of charge	charge conjugation parity (C)
inversion of space	space parity (P)
inversion of time	time parity (T)
inversion of charge and space	(CP)
inversion of charge, space, and time	(CPT)

non locality

Category: phenomenon

Definition: A linkage between simultaneous events.

Related terms: locality

Symbol: not applicable

SI units: not applicable

Remarks:

Note that in simultaneous events, there is no time for a signal to be transmitted even at the speed of light.

nonrelativistic quantum mechanics

Category: branch of physics

Definition: That branch of quantum mechanics that deals with systems in which the particles are moving slowly compared to the velocity of light and in which particles are neither created or destroyed.

Related terms:

For a list of other related terms see: quantum mechanics

Symbol: not applicable

SI units: not applicable

Remarks:

Category: phenomenon

Definition: Normal matter is matter that consists of normal particles.

Antimatter is matter composed entirely of antiparticles.

Related terms: ordinary matter

For a list of other related terms see: particle categories

Symbol: not applicable

SI units: not applicable

Remarks:

Gauge bosons are considered to be normal matter because they occur naturally even though they they consist of both normal quarks and antiquarks.

Whether antimatter occurs naturally in any part of the universe is unknown.

Why normal matter prevails over antimatter is also unknown.

normal particle
antiparticle

Category: category of particle

Definition: Normal particle is a generic term that is an extension of the term ordinary particle to include the particles of the second and third generations of leptons and quarks and particles composed of the second and third generation quarks.

By similar, we mean that the signs of the internal quantum numbers are the same as the corresponding particles in the first generation.

Antiparticle is a generic term for particles that are like normal particles except that the signs of all the internal quantum numbers are reversed.

For a list of other related terms see: particle categories

Symbol: not applicable

SI units: not applicable

Remarks:

Antiparticles have the same mass as their corresponding normal particles but the opposite sign for all other charges.

The normal leptons are:

generation	charged leptons	neutrinos
1st	electron	electron neutrino
2nd	muon	muon neutrino
3rd	tauon	tauon neutrino

The normal quarks are:

generation	quarks	quarks
1st	up quark	down quark
2nd	charmed quark	strange quark
3rd	top quark	bottom quark

Gauge bosons are included within the meaning of normal particle even though they consist of normal quarks and antiquarks.

Every normal particle has a corresponding antiparticle and vice versa.

If a particle has no internal quantum numbers, then the antiparticle is identical to the normal particle and vice versa.

normalization

Category: mathematical operation

Definition: An mathematical operation by which a normalizing factor is introduced into an mathematical function so that the integral of the mathematical function over all space is equal to 1.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

An example of the result of a normalization is:

y' = Ay dx = 1

Definition: That branch of physics that deals with the structure and properties of atomic nuclei.

Related terms:

For a list of other related terms see: branches of physics

Symbol: not applicable

SI units: not applicable

Remarks:

nuclear reaction

Category: phenomenon

Definition: A reaction between an atomic nucleus and a high energy particle or photon leading to the creation of a modified nucleus and the possible ejection of one or more particles and perhaps a large amount of energy.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

nucleon

Category: category of particle

Definition: A generic term for a proton or a neutron.

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

nucleon number
atomic mass number

Category: scalar quantity

Definition: The number of nucleons (protons and neutrons) in the nucleus of an atom.

Related terms: neutron number, proton number

For a list of other related terms see: relative atomic mass

Symbol: A

SI units: dimensionless

Remarks:

In the nucleus of an atom there are:

symbol	particles	name	alternate name
Z	protons	proton number	atomic number
N	neutrons	neutron number	neutron number
A=N+Z	nucleons	nucleon number	atomic mass number

nucleosynthesis

Category: phenomenon

Definition: The creation of chemical elements by nuclear reactions.

Related terms: reaction

Symbol: not applicable

SI units: not applicable

Remarks:

nucleus
atomic nucleus

Category: object

Definition: The central part of an atom.

Related terms:

For a list of other related terms see: atom

Symbol: not applicable

SI units: not applicable

Remarks:

The nucleus of an atom consists of protons and neutrons.

nuclide

Category: category of particle

Definition: A species of atom characterized by the number of protons, the of number neutrons, and the energy content.

Related terms:

For a list of other related terms see: atom

Symbol: ??

SI units: not applicable

Remarks:

null geodesic

Category: concept

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

In this glossary, the term object is used if the thing is an atom or larger, and the term particle is used if the thing is smaller than an atom.

Usually a (more or less) rigid object is intended.

odd function

Category: concept

Definition: A mathematical function that has the following characteristic:

f(x) = -f(x)

Related terms: even function

Symbol: not applicable

SI units: not applicable

Remarks:

A mathematical function can be even, odd, or neither.

Sine is an odd function.

Cosine is an even function.

e^x is neither odd nor even.

odd half integer

Category: number

Definition: A value such as 1/2, 3/2, 5/2, ...

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

odd parity

Category: concept

Definition: If a mathematical function changes sign when coordinates are reversed, the mathematical function is said to have odd parity.

f(x,y,z,) = -f(-x,-y,-z)

Related terms: even parity

For a list of other related terms see: parity

Symbol: not applicable

SI units: not applicable

Remarks:

ohm

Definition: The unit of measurement of electric resistance in the SI system of units.

Related terms: none

Symbol: W

SI units: 1 ohm = 1 volt / ampere = 1 newton × meter × second / coulomb²

Remarks:

By definition, an ohm is the resistance between two points on a conductor through which an electric current of one ampere flows as a result of a electric potential difference of one volt applied between the points.

Ohm's law

Category: law

Statement: The electric current in a conductor is directly proportional to the electric potential difference applied to it.

Related terms: electric resistance

Symbol: not applicable

SI units: not applicable

Remarks:

open system

Category: concept

Definition: A system that may exchange mass or energy with the surroundings.

Related terms: closed system, isolated system

Symbol: not applicable

SI units: not applicable

Remarks:

open universe

Category: concept

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: ??

Remarks:

orbital quantum number
orbital angular momentum quantum number
azimuthal quantum number

Category: quantum number

Definition: A quantum number that governs the orbital angular momentum of a particle.

Related terms:

For a list of other related terms see: quantum number

Symbol: l

Values: 0, 1/2, ...

Remarks:

order of magnitude

Category: concept

Definition: The value of a number within a factor of 10.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

ordinal number

Category: concept

Definition: A number that designates the place occupied by an item in an ordered sequence.

Related terms: cardinal number

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

1st, 2nd, 3rd, ...

ordinary differential equation

Category: mathematical expression

Definition: A differential equation that does not contain any partial derivatives

Related terms: partial differential equation

Symbol: not applicable

SI units: not applicable

Remarks:

ordinary matter

Category: phenomenon

Definition: Ordinary matter is matter that occurs naturally.

That would be: the first generation of normal leptons (i.e. electrons and electron neutrinos) and particles that consist of the first generation of normal quarks (i.e. normal protons and normal neutrons).

The second and third generations of leptons and quarks, the quarks themselves, and antiparticles are not considered to be ordinary matter.

Related terms: antimatter, normal matter

For a list of other related terms see: particle categories

Symbol: not applicable

SI units: not applicable

Remarks:

The antimatter equivalent of ordinary matter would consist of antiprotons, antineutrons, positrons, and electron antineutrinos.

ordinary particle

Category: category of particle

Definition: A generic term for particles that occur naturally.

For a list of other related terms see: particle categories

Symbol: not applicable

SI units: not applicable

Remarks:

The particles that occur naturally are:

the first generation of leptons (electrons and electron neutrinos)
the first generation of quarks (up quarks and down quarks)
particles that consist of the first generation of quarks
gauge bosons

ordinate

Category: concept

Definition: The Cartesian coordinate obtained by measuring parallel to the y axis.

Related terms: none

Symbol: varies (often y)

SI units: not applicable

Remarks:

origin

Category: concept

Definition: The intersection of the coordinate axes.

Related terms:

For a list of other related terms see: coordinate systems

Symbol: not applicable

SI units: not applicable

Remarks:

orthogonal

Category: concept

Definition: Mutually perpendicular.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

oscillating system
oscillator

Category: concept

Definition: A system which oscillates.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

oscillation

Category: phenomenon

Category: property

Definition: Parity is a property of a wave function that characterizes its behavior under simultaneous reversal of all spatial coordinates through the origin.

The wave function is said to have even parity if:

f(x,y,z) = f(-x,-y,-z)

and odd parity if:

f(x,y,z) = -f(-x,-y,-z)

If these two equations are combined:

f(x,y,z) = P(-x,-y,-z)

then P is the quantum number, parity.

Symbol: P

Values: -1, 0, or +1

Remarks:

Parity is the eigenvalue of the mathematical operation of space inversion.

Parity has meaning only for fields or waves and therefore has meaning only in classical field theory or quantum mechanics.

Parity is conserved in all particle interactions except weak interactions.

Category: operator

Definition: An operator that indicates partial differentiation.

Related terms:

For a list of other related terms see: differentiation

Symbol: ¶,Ñ

SI units: not applicable

Remarks:

¶ is the symbol for the partial differential operator with respect to one variable.

Ñ (del or nabla) is the partial differential operator in 3 dimensions.

partial differentiation
partial derivative

Category: mathematical operation

Definition: Differentiation with respect to one variable while all other variables are held constant.

Related terms:

For a list of other related terms see: differentiation

Symbol: ¶

SI units: not applicable

Remarks:

partial pressure

Category: scalar quantity

Definition: That part of the pressure of a gas that is due to a particular molecular species that is present.

Related terms: none

Symbol: p

SI units: pascals = newtons / meter²

Remarks:

The partial pressure of a component of a gas is equal to the number fraction of molecules times the pressure of the gas.

particle

Category: phenomenon

Definition: A portion of matter that is smaller than an atom.

As of June 2001, the meaning is not generally understood to extend to the "strings" of string theory.

For a list of other related terms see: atom, object, particle categories

Symbol: varies

SI units: not applicable

Remarks:

All particles exhibit both particle-like and wave-like properties.

Leptons, quarks, and particles composed of quarks exhibit primarily particle-like properties.

Gauge bosons exhibit primarily wave-like properties .

A particle is usually thought of as occupying space and having mass. However, electrons are thought to be point particles and neutrinos may not have mass. Nevertheless, electrons and neutrinos are considered to be particles.

particle characteristics

Elementary particles

category	subcategory	force	type	statistics	spin
leptons	electrons	electromagnetic force	fermion	Fermi-Dirac	1/2
"	neutrinos	weak force	fermion	Fermi-Dirac	1/2
quarks	quarks	strong force	fermion	Fermi-Dirac	1/2
gauge bosons	photons	electromagnetic force	boson	Bose-Einstein	1
"	intermediate vector bosons	weak force	boson	Bose-Einstein	1
"	gluons	strong force	boson	Bose-Einstein	1
"	gravitons	gravitational force	boson	Bose-Einstein	2
"	Higgs	??	boson	Bose-Einstein	0

Composite particles

category	subcategory	force	type	statistics	spin
hadrons	baryons	strong force	fermion	Fermi-Dirac	odd half integer
"	mesons	strong force	boson	Bose-Einstein	integer

particle interaction

Category: phenomenon

Definition: An interaction between particles.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

particle physics

Category: branch of physics

Definition: That branch of physics that deals with the properties, behavior, and interactions of the elementary particles.

Related terms:

For a list of other related terms see: branches of physics

Symbol: not applicable

SI units: not applicable

Remarks:

Related fields of study are:

particle	particle physics
molecule	chemistry
atom	atomic physics
atomic nuclei	nuclear physics
lepton / quark	particle physics

particle-like

Category: concept

Definition: Resembling a particle in form, behavior, or characteristics

Related terms: wave-like

Symbol: not applicable

SI units: not applicable

Remarks:

partition function

Category: mathematical expression

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

pascal

Photons mediate electromagnetic interactions.

Definition: The unit of measurement of pressure or stress in the SI system of units.

Related terms: none

Symbol: Pa

SI units: 1 pascal = 1 newton / meter²

Remarks:

Pascal's principle

Category: principle

Statement: Pressure applied to a confined fluid increases the pressure throughout the fluid by the same amount.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Pauli exclusion principle
exclusion principle

Category: principle

Statement: In any system, two identical fermions can not have the same set of quantum numbers.

Related terms: none

Category: scalar quantity

Definition: The ratio of the magnetic flux density in a medium to the external magnetic field strength inducing the magnetic flux (F).

Related terms: permeability of free space

For a list of other related terms see: electricity and magnetism

Symbol: μ

SI units: henrys / meter = newton × seconds² / coulomb²

Remarks:

The mathematical expression for permeability is:

μ = B / H

permeability of free space
magnetic constant

Category: fundamental constant

Definition: The ratio of the magnetic flux density in free space to the external magnetic field strength inducing the magnetic flux (F).

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: μ₀

Values: 4π × 10^-7 henrys / meter = newton × seconds² / coulomb²

Remarks:

The permeability of free space multiplied by the permittivity of free space is equal to 1 over the speed of light squared.

μ₀ε₀ = 1 / c²

permittivity
electric permittivity

Category: scalar quantity

Definition: The ratio of the electric displacement (D) in a dielectric medium to the applied electric field strength.

Related terms: permittivity of free space

For a list of other related terms see: electricity and magnetism

Symbol: ε

SI units: farads / meter = coulombs² / newton × meter²

Remarks:

Permittivity is a measure of the ability of dielectric medium to resist the flow of electric charge.

The permittivity of a conductor is 0.

permittivity of free space
electric constant

Category: fundamental constant

Definition: The ratio of the electric flux density (D) in free space to the applied electric field strength.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: ε₀

Values: 8.854 187 817 × 10^-12 farads / meter = coulombs² / newton × meter²

Remarks:

The permeability of free space multiplied by the permittivity of free space is equal to 1 over the speed of light squared.

μ₀ε₀ = 1 / c²

perpendicular
normal

Category: concept

Definition: At right angles to another line or surface.

Related terms: tangent

Symbol: not applicable

SI units: not applicable

Remarks:

perturbation

Category: concept

Definition: A deviation from the usual motion.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

phase

Category: concept

Definition:

A point in the period of a periodically varying quantity in relation to a base point.
A homogeneous, distinct, and separable portion of a nonhomogeneous substance.

Related terms: phase of matter, phase of wave motion

Symbol: not applicable

SI units: not applicable

Remarks:

phase angle

Category: scalar quantity

Definition: The angle between the two vectors that represent two sinusoidally varying quantities having the same frequency.

Related terms: phase difference

Symbol: φ

SI units: radians

Remarks:

phase difference

Category: scalar quantity

Definition: The difference in the phase of two periodically varying quantities that have the same frequency.

Related terms: phase angle

Symbol: φ

SI units: seconds or radians

Remarks:

A phase difference may be expressed as a fraction of a period, a time interval, or an angle.

If two periodically varying quantities are not sinusoidal but have the same fundamental frequency, then the phase difference is the difference of phase of the two frequencies.

phase invariance
phase symmetry

Category: concept

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

phase of matter

Category: concept

Definition: A distinct state of aggregation of matter.

Related terms: gas, liquid, solid, plasma

Symbol: not applicable

SI units: not applicable

Remarks:

It is usually said that there are three phases of matter: gaseous. liquid, and solid, The plasma state is sometimes added.

A system may consist of one gaseous phases, one or more liquid phases, and one or more solid phases.

phase of wave motion

Category: concept

Definition: A point in the period of a periodically varying quantity in relation to a base point.

Related terms: in phase, periodic motion, phase difference

Symbol: not applicable

SI units: not applicable

Remarks:

Phase can be expressed as a fraction of a period, a time interval, or an angle.

phase shift

Category: scalar quantity

Definition: Of a periodic quantity, any change in the phase of one quantity or in the phase difference between two or more quantities.

Related terms: none

Symbol: ??

SI units: hertz = cycles / second

Remarks:

phase space

Category: concept

Definition: A multi-dimensional space in which the coordinates represent the variables required to specify the state of the system.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

A six-dimensional space incorporating three dimensions of position and three of linear momentum.

phase transition

Category: phenomenon

Definition:

In thermodynamics, a change from one phase of matter to another.
In cosmology, a change in which one of the four fundamental forces separated from a unified force.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

phase velocity
phase speed

Category: scalar quantity

Definition: The speed at which a phase of a wave is propagated.

Related terms: group velocity

Symbol: v_p

SI units: meters / second

Remarks:

The mathematical expression for phase velocity is:

v_p = λ / T = υ / k

where:

λ = wavelength

T = period

υ = frequency

k = wave number

Phase velocity is not limited by the speed of light.

phenomenon

Category: common term

Definition: An observable event, or object. Something known directly or indirectly through the senses as opposed to through thought alone.

Related terms: concept

Symbol: not applicable

SI units: not applicable

Remarks:

philosophy

Category: philosophical term

Definition: The pursuit of knowledge of reality by chiefly speculative means rather than the observational means used in science.

Related terms: mathematics, physics, science

Symbol: not applicable

SI units: not applicable

Remarks:

phonon

Category: particle

Definition: A quantum of vibrational energy.

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

photino

Category: hypothetical particle

Definition: The supersymmetric partner of the photon.

Related terms:

For a list of other related terms see: supersymmetry

Symbol: ??

SI units: not applicable

Remarks:

photoelectric constant

Category: fundamental constant

Definition: The ratio of the Planck constant to the electric charge of the electron.

Related terms: none

Symbol: ??

SI units: 4.1357 × 10^-15 joule × second / coulomb

Remarks:

photoelectric effect

Category: phenomenon

Definition: The liberation of electrons from matter by electromagnetic radiation of specific frequencies.

Related terms: quantum mechanics

Symbol: not applicable

SI units: not applicable

Remarks:

photo ionization

Category: phenomenon

Definition: ionization of an atom or molecule by electromagnetic radiation.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

photon

Category: elementary particle

Definition: A quantum of electromagnetic radiation.

The properties of a photon are:

property	value
electric charge	0
rest mass	0
spin	1
mean lifetime	infinite

Related terms: gauge bosons

For a list of other related terms see: particle categories

Symbol: γ

SI units: not applicable

Remarks:

Use of the term photon implies reference to the particle-like behavior of electromagnetic radiation as contrasted with its wave-like behavior.

A photon is a gauge boson.

The energy of a photon is given by:

E = hυ

where:

υ = frequency

Photons have zero rest mass.

physical

Category: common term

Definition:

Having material existence.
Perceptible, directly or indirectly, through the senses and subject to the laws of nature.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

physical process

Category: concept

Definition: A process involving physical things.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

physicists

Category: common term

Definition: A person who has contributed to the study of physics.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

The following physicists are mentioned in this glossary.

Ampere, Archimedes, Argand, Avogadro, Balmer, Becquerel, Biot, Bohr, Boltzmann, Bose, Boyle, Brackett, Brown, Dalton, de Broglie, Dirac, Doppler, Einstein, Euclid, Euler, Fahrenheit, Faraday, Fermat, Fermi, Feynman, Fourier, Friedmann, Galileo, Gauss, Gay-Lussac, Glashow, Green, Hamilton, Heaviside, Heisenberg, Hermite, Higgs, Hilbert, Hooke, Hubble, Joule, LaGrange, LaPlace, Le Chatelier, Legendre, Lenz, Lobachevski, Lorentz, Lyman, Maxwell, Minkowski, Newton, Noether, Ohm, Pascal, Paschen, Pauli, Pfund, Planck, Poisson, Poynting, Pythagoras, Raman, Rayleigh, Reynolds, Riemann, Rutherford, Rydberg, Salam, Savart, Schrodinger, Schwarzschild, Stefan, Stokes, Thomson, Weinberg, Wien, Young, Yukawa, Zeeman

physics

Category: science

Definition: The science that deals with space, time, forces, matter, energy and their interactions.

Symbol: not applicable

SI units: not applicable

Remarks:

Physics can be subdivided in several ways.

By historical era:

classical physics prior to about 1905
modern physics after 1905

By the velocities involved:

nonrelativistic velocities v<<c
relativistic velocities otherwise

By whether or not quantum effects are significant:

quantum mechanics quantum effects significant
non-quantum mechanics usually implied by omission

By Subject: (the following is not an exhaustive list)

atomic physics
dynamics
electricity and magnetism
electrodynamics
electrostatics
kinematics
mechanics
magnetostatics
nuclear physics
particle physics
quantum chromodynamics
quantum electrodynamics
quantum flavordynamics
statics

By approach used:

chaos theory
field theory
statistical mechanics

At one time physics was called natural philosophy.

pi

Category: fundamental constant

Definition: In a Euclidean space, the ratio of the circumference of a circle to the diameter of the circle.

Related terms: none

Symbol: π

Value: 3.141 592 653 589 793

Remarks:

planck

Definition: The unit of measurement of action.

Related terms: none

Symbol: ??

SI units: 1 planck = 1 joule × second

Remarks:

Planck constant

Category: fundamental constant

Definition: The ratio of a quantum of energy to its frequency. The Planck constant is a universal constant.

Related terms: none

Symbol: h

Values: 6.626 076 5 × 10^-34 joule × seconds

Remarks:

The Planck constant shows up in many circumstances particularly in quantum mechanics.

For example, the energy of a photon is given by:

E = hυ

where υ is the frequency of the light wave.

It often happens that the Planck constant appears with a factor of 1/2π. For convenience in notation, the mathematical expression h / 2π has been give its own symbol: .

= h / 2π

The value of is 1.0546 × 10^-34 joule × second

Planck length

Definition: A unit of measurement of length.

Related terms: none

Symbol: ??

Values: 1 Planck length = 1.6160 × 10^-35 meters

Remarks:

Planck length is a function of other constants:

where:

Planck mass

Category: scalar quantity

Definition: A unit of measurement of mass.

Related terms: none

Symbol: ??

SI units: 2.1768 × 10^-8 kilogram

Remarks:

Planck mass is a function of other constants:

where:

Planck time

Category: fundamental constant

Definition: The time required for a photon to travel a distance equal to the Planck length at the speed of light.

Related terms: none

Symbol: ??

SI units: 1.7086 × 10^-43 second

Remarks:

Planck time is a function of other constants:

where:

Planck's law
Planck's radiation law

Category: law

Statement: The energy of electromagnetic radiation is confined to small indivisible packets or photons each of which has an energy h × f where h is the Planck constant and f is frequency of the electromagnetic radiation.

Definition: The energy of electromagnetic radiation is confined to small indivisible "packets". These packets are called photons.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of the Planck radiation law is:

where:

u = energy density

k = Boltzmann constant

T = thermodynamic temperature

The energy of a packet is given by:

E = hυ

where:

υ = frequency

plane

Category: geometric element

Definition: A surface of such a nature that a straight line joining two of its points likes wholly in the surface.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

plane wave

Category: phenomenon

Definition: A wave in which the wavefront is a straight line or a plane.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

plasma

Category: substance

Definition: A highly or completely ionized substance.

Related terms: phase of matter

Symbol: not applicable

SI units: not applicable

Remarks:

Plasmas are formed at very high temperature (> 20,000 kelvin) or by photoionization.

point

Category: geometric element

Definition:

A position.
A particular value of a quantity.
A geometric element that has no extension and that is located by coordinates in a coordinate system.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

poise

Definition: The unit of measurement of viscosity in the cgs system of units.

Related terms: none

Symbol: P

Values: 1 poise = 0.1 pascal × second

Remarks:

Poisson's equation

Category: mathematical expression

Statement: An equation that states that the Laplacian of a mathematical function is equal to another, non-zero, mathematical function.

Related terms: Laplace's equation

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of Poisson's equation is:

Ñ²f = g

where:

f = f(x,y,z)

g = g(x,y,z)

Examples:

The Laplacian of an electric potential is equal to minus the divergence of the electric field strength.

Ñ²V = -Ñ+E = -ρ / ε₀

polarity

Category: concept

Definition: The condition of a system in which opposite or contrasting properties are exhibited in opposite or contrasting parts or directions.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

polarization
polarized
unpolarized

Category: phenomenon

Definition: The way in which the direction of oscillation of electromagnetic radiation varies.

For a list of other related terms see: electric polarization

Related terms: none

Symbol: p

SI units: not applicable

Remarks:

If the direction of vibration does not vary in any regular manner, the radiation is said to be unpolarized.

If the electric field resides entirely in one plane, the radiation is said to be plane polarized.

If the electric field rotates with constant angular velocity, the radiation is said to be circularly polarized.

If the electric field not only rotates but also varies in magnitude, the radiation is said to be elliptically polarized.

pole

Category: concept

Definition: The place toward which lines of magnetic flux converge or diverge.

Related terms: monopole, magnetic pole

Symbol: not applicable

SI units: not applicable

Remarks:

polynomial

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

position

Category: common term

Definition:

The point in an extent at which something is located.
The ordinal number of an item in an ordered sequence.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

position vector

Category: vector quantity

Definition: A vector representing in direction and magnitude the difference in position between a given point and the origin.

Related terms: displacement vector

Symbol: r

SI units: meters

Remarks:

The scalar components of the position vector are the coordinates of the point in the coordinate system.

In Cartesian coordinates the position vector is given by:

r = x i^ + y j^ + z k^

where:

r is the position vector

(x,y,z) are the coordinates of the point.

i^, j^, k^ are the unit vectors for the x,y,z axes respectively

positive

Category: concept

Definition:

Greater than zero.
Extending or generated in a direction customarily taken as increasing.
Being, related to, or charged with electricity of which the proton is the elementary unit of measurement.

Related terms: negative

Symbol: (+)

SI units: not applicable

Remarks:

positive number

Category: concept

Definition: A number that is greater than zero.

Related terms: negative

Symbol: (+)

SI units: not applicable

Remarks:

postulate

Category: generic term

Definition: A hypothesis advanced as an essential presupposition, condition, or premise of a train of reasoning.

Related terms: axiom

For a list of other related terms see: proposition

Symbol: not applicable

SI units: not applicable

Remarks:

potential difference

Category: scalar quantity

Definition: Potential difference is the work required to move a unit quantity from one point to another point in a force field .

Related terms:

For a list of other related terms see: potential

Symbol: varies

SI units: joules / unit of the quantity = newton × meters / unit

Remarks:

The work done is independent of the path taken between the two points.

The energy resides in the system.

potential energy
potential

Category: scalar quantity

Definition: If an object is part of a system that exerts a force on the object, then the work required to move the object from one point in the range of the force to a second point in the range of the force with no net change in the kinetic energy or internal energy of the object is the change in potential energy in the system.

Symbol: U

SI units: joules = newton × meters

Remarks:

The work done is independent of the path taken between the two points.

Potential energy is often spoken of as if it resides in the subject object. However, this is not the case; the energy resides in the system as a whole.

There is no such thing as an absolute value of potential energy; only changes in potential energy are meaningful.

The required energy can come from a source external to the system or internal to the system.

In some cases, point one is taken to be a point in the range of the force at which the force is zero, such as the point at which a spring is fully extended or a point that is at infinite distance from the source of a field.

In some cases, point one is taken to be a reference point and the potential energy at the reference point is taken to be zero.

Commonly cited systems include:

a object elevated above the surface of the earth
a object and a spring
the earth and the moon

Examples:

The force (F) exerted on a object by a spring that acts in the x direction is given (approximately) by Hooke's law:

F = -k(x-x₀)x^

where:

k = spring constant

x₀ = point at which the spring is relaxed

x-x₀ = displacement from point x₀

x^ = unit vector in the x direction

The minus sign indicates that the force is opposite in direction to the displacement.

If another external force is applied to move the object from x₀ to x, then the work required from the external agent is given by:

W =

and

DU = W

where:

DU = change in potential energy of the system

W = the work done on the system

Note that the external force must be opposite in direction and therefore in sign to the force exerted by the spring.

potential gradient

Category: vector quantity

Definition: The rate of change of potential with respect to distance measured in the direction of maximum rate of change.

Related terms: none

Symbol: ??

SI units: joules / meter = newtons

Remarks:

Examples:

The mathematical expression for the gradient of electric potential is:

E = -ÑV

where:

V = electric field potential

potential well

Category: phenomenon

Definition: A region in a force field in which the potential reaches a minimum.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

pound

Definition: The unit of measurement of mass in the fps system of units

Related terms: none

Symbol: lb

SI units: 1 pound = 0.453 592 37 kilogram

Remarks:

power

Category: scalar quantity

Definition: The rate at which energy is expended or work is done.

Related terms: none

Symbol: P

SI units: watts = joules / second = newton × meters / second

Remarks:

Poynting vector

Category: pseudovector quantity

Definition: The energy transmitted by electromagnetic radiation per unit of area per unit of time.

Related terms: none

Symbol: S

SI units: joules / meter² × second = newtons / second

Remarks:

At a point, the Poynting vector is equal to the cross product of the electric field strength and the magnetic field strength at the point.

The mathematical expression of the Poynting vector in free space is:

quantum number	state specified
n (the principal quantum number)	energy level
l	total angular momentum
m_l	z component of total angular momentum
m_s	spin

principle

Category: generic term

Definition: A scientific proposition that is generally accepted as true and fundamental.

Related terms:

For a list of other related terms see: proposition

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

causality principle
complementarity principle
conservation of charge principle
conservation of energy principle
conservation of momentum principle
continuity principle
correspondence principle
equipartition of energy principle
invariance principle
Le Chatelier's principle
least action principle
least time principle
Hamilton's principle
Pauli exclusion principle
superposition principle
similarity principle
stationary time principle
uncertainty principle (Heisenberg)

principle of conservation
conservation

Category: generic term

Definition: A statement that a specific quantity is unchanged by a physical process.

Related terms:

proper length
proper distance

Category: scalar quantity

Definition: The distance between two points or objects whose position is measured at the same time by observers at rest with respect to the points

Related terms: none

Symbol: ??

SI units: meters

Remarks:

proper time
proper time interval

Category: scalar quantity

Definition: Time as it would be measured by an observer in the proper frame is called proper time by an observer in the lab frame.

Related terms:

For a list of other related terms see: reference frame

Symbol: τ

SI units: seconds

Remarks:

A proper time interval is related to a lab time interval as follows:

Δτ = γΔt

where:

Δτ = proper time interval

nonrelativistic quantum mechanics

Δt = lab time interval

property

Category: common term

Definition: An intrinsic or essential characteristic, quantity, or quality of a thing.

Related terms: intrinsic

Symbol: varies

SI units: not applicable

Remarks:

A quantity that is related to the motion of a particle, such as velocity, energy, or momentum, is not intrinsic to the particle and therefore is not spoken of as a property of the particle.

The term property is sometimes applied to the effect that a thing has on another thing. For example, gravitational force can be said to be a property of mass. This use of the term is discouraged.

Example:

A negative electric charge is a property of an electron; if a particle does not have a negative electric charge, it is not an electron.

proposition

Category: generic term

Definition: A statement in words or mathematical expressions of a concept that can be believed, doubted, or denied or is true or false.

Related terms: axiom, hypothesis, law, model, postulate, principle, theorem, theory

Symbol: not applicable

SI units: not applicable

Remarks:

term	implication
axiom	a self-evident truth
postulate	an essential presupposition
hypothesis	subject to verification
law	true in specific circumstances
model	described in terms of familiar phenomena
principle	a general law covering multiple cases
proposition	offered for consideration
theorem	a part of a more general theory
theory	a systematic and complete view of a subject

proton
normal proton
antiproton

Category: particle

Definition: A proton is a particle of matter that is composed of quarks and has an electric charge.

A normal proton is a normal particle and has a positive electric charge.

An antiproton is the antimatter equivalent of a normal proton and has a negative electric charge.

The properties of a proton are:

property	value for a normal proton
electric charge	+1
rest mass	938.28 MeV / c² = 1672.62 × 10^-30 kilogram
spin	1/2
mean lifetime	infinite

Related terms:

For a list of other related terms see: particle categories

Symbol: p

SI units: not applicable

Remarks:

All protons interact through the strong force, electromagnetic force, weak force, and gravitational forces.

A proton has a mass roughly equal to that of a neutron and about 1836.2 times that of an electron.

A proton is a fermion (since it has spin of 1/2) and a hadron (since it takes part in strong interactions) and a baryon (since it is both a fermion and a hadron).

proton mass

Category: fundamental constant

Definition: The rest mass of a proton.

Related terms: none

Symbol: m_p

Values: 1 proton mass - 1.6276 × 10^-27 kilograms = 938.28 MeV / c²

Remarks:

pseudo

Category: common term

Definition:

Alike in some ways but not in all.
Artificial.

Symbol: not applicable

SI units: not applicable

Remarks:

pseudo acceleration

Category: pseudovector quantity

Definition: An artificial acceleration corresponding to a pseudoforce.

Related terms: none

Symbol: ??

SI units: meters / second²

Remarks:

pseudo force

Category: vector quantity

Definition: An artificial force that allows an observer in a noninertial reference frame (i.e. a reference frame that is rotating or accelerating) to describe the motion of a object in terms of Newton's laws of motion.

Related terms:

For a list of other related terms see: force

Symbol: ??

SI units: not applicable

Remarks:

pseudo scalar meson

Category: category of particle

Definition: A meson in which one quark has spin +1/2 while the other quark has spin -1/2 with the result that the meson has spin 0. In this context "pseudoscalar" means spin 0.

Related terms: vector meson

Symbol: varies

SI units: not applicable

Remarks:

pseudoscalar quantity
pseudo scalar

Category: concept

Definition: A quantity that is defined by a magnitude only but that is distinguished from a scalar in that it is an odd function, i.e. it changes sign when all spatial coordinates are reflected through the origin.

Symbol: varies

SI units: not applicable

Remarks:

Examples:

pressure
volume
the triple product of three vectors: a • (b ´ c)

pseudovector quantity
pseudo vector
axial vector

Category: concept

Definition: A quantity that is situated along an axis, but the direction of which is arbitrary.

A pseudovector changes sign when all spatial coordinates are reflected through the origin.

Symbol: bold letter

SI units: not applicable

Remarks:

A true vector is a symmetric first-order tensor. A pseudovector is really not a vector but a skew-symmetric second-order tensor.

The cross product of two vectors is a pseudovector. Notice that the direction of a cross product is normal to the plane of rotation but that there are still two choices for the direction. The choice of the direction is determined by a convention: the right-hand rule.

In a space inversion the handedness of the coordinate system is changed, however the choice of direction for a pseudovector is similar to a true vector except for the change of sign under space inversion.

In a theory with parity invariance, vectors and pseudovectors may not be added.

Examples:

pseudovector quantities are:

angular momentum

magnetic field

pulse

Category: phenomenon

Definition: A transient variation in a quantity whose value is normally constant.

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

Pythagorean theorem

Category: theorem

Category: common term

Definition: A characteristic of a thing that is measurable in duration, extent, intensity, magnitude, volume, or value.

Related terms: basic quantities, quality

Symbol: varies

SI units: not applicable

Remarks:

If a quantity is intrinsic to a thing it is called a property of the thing instead of a quantity.

quantized
quantized property
quantized quantity

Category: concept

Definition: Occurring only in discrete values.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

For a list of quantities that may be quantized, see conserved quantities.

quantum

Category: concept

Definition: The smallest amount of energy that a system can gain or lose.

Related terms: quantum theory

Symbol: ??

SI units: not applicable

Remarks:

quantum chromodynamics
chromodynamics
QCD

Category: theory

Definition: A gauge theory of strong interactions.

Related terms:

For a list of other related terms see: interaction

Symbol: not applicable

SI units: not applicable

Remarks:

Quantum chromodynamics is based on the idea that certain gauge bosons called gluons carry the strong force between particles that possess the color charge.

Quantum chromodynamics applies both relativity and quantum theory to strong interactions.

quantum effect

Category: phenomenon

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

quantum electrodynamics
QED

Category: theory

Definition: A gauge theory of electromagnetic interactions.

Related terms:

For a list of other related terms see: interaction

Symbol: not applicable

SI units: not applicable

Remarks:

Quantum electrodynamics is based on the idea that certain gauge bosons called photons carry the electrically charged particles that possess electric charge.

Quantum electrodynamics applies both relativity and quantum theory to electromagnetic interactions.

quantum field

Category: generic term

Definition: A field in which the field quantity is quantized.

Related terms:

For a list of other related terms see: field

Symbol: not applicable

SI units: not applicable

Remarks:

quantum field theory

Category: generic term

Definition: A quantum mechanical theory in which particles are represented by wave fields whose normal modes of oscillation are quantized.

For a list of other related terms see: quantum mechanics

Symbol: not applicable

SI units: not applicable

Remarks:

Applications of quantum field theory include:

systems in which particle creation and destruction can occur.
description of elementary particles and their associated wave fields at relativistic velocities.
nonrelativistic quantum field theory for systems of many particles.

Quantum field theory deals with systems possessing an infinite number of degrees of freedom such as electromagnetic fields and gravitational fields.

quantum field vacuum

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

quantum flavordynamics
flavordynamics
QFD

Category: theory

Definition: A gauge theory of weak interactions.

Related terms:

For a list of other related terms see: interaction

Symbol: not applicable

SI units: not applicable

Remarks:

Quantum flavordynamics is based on the idea that certain gauge bosons called intermediate vector bosons carry the weak force between particles that possess the weak charge.

Quantum flavordynamics applies both relativity and quantum theory to weak interactions.

quantum gravitation

Category: theory

Definition: A gauge theory of gravitational interactions.

Related terms: gravitation

For a list of other related terms see: interaction

Symbol: not applicable

SI units: not applicable

Remarks:

Quantum gravitation is based on the idea that certain gauge bosons called gravitons carry the gravitational force between particles that possess the mass.

quantum mechanical system

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

quantum mechanics
quantum physics

Category: branch of physics

Definition: That branch of physics in which the quantum theory plays a role.

Symbol: not applicable

SI units: not applicable

Remarks:

Quantum mechanics generalizes and supersedes classical mechanics and Maxwell's equations.

In some contexts, the meaning of quantum mechanics is restricted to nonrelativistic quantum mechanics.

In quantum mechanics the quantum theory is applied to matter, electromagnetic radiation, and the interaction between matter and electromagnetic radiation.

There are three domains of applicability:

relativistic quantum mechanics

quantum field theory

Category: theory

Statement: Certain physical quantities can take on only discrete values.

Related terms: quantum mechanics

Symbol: not applicable

SI units: not applicable

Remarks:

For example, the energy of electromagnetic radiation can take on only discrete values.

The energy of electromagnetic radiation is given by:

E = nhν

where:

E = energy (joules)

n = integer (0, 1, 2, 3, ...)

h = Planck constant (6.626 × 10^-34 joule × second)

ν = frequency (cycles per second)

One implication of the quantum theory is that electromagnetic radiation has particle-like properties.

The study of the implications of the previous statement is called quantum mechanics.

quark
normal quark
antiquark

Category: category of particle

Definition: Quark is a generic term for all elementary particles that take part in strong interactions and have spin 1/2.

A normal quark is a normal particle.

An antiquark is the antimatter equivalent of a quark.

There are six types (or flavors) of normal quarks arranged in exactly 3 generations; each generation having exactly 2 members.

generation	electric charge = +2/3	quantum number	electric charge = -1/3	quantum number
1st	up quark	upness	down quark	downness
2nd	charmed quark	charm	strange quark	strangeness
3rd	top quark	truth	bottom quark	beauty

Related terms:

For a list of other related terms see: flavor, particle categories

Symbol: not applicable

SI units: not applicable

Remarks:

There are three principal categories of elementary particles:

leptons
quarks
gauge bosons

Each generation has a set of three quantized properties called colors associated with it.

Each flavor has a corresponding antiparticle.

Thus there are 6*2*3 = 36 quarks in total.

Quarks do not appear as independent particles, only in combination with other quarks. These combinations are called hadrons.

quark confinement

Category: theory

Definition: The theory that quarks can not exist outside of a hadron.

Related terms: free state

Symbol: not applicable

SI units: not applicable

Remarks:

Definition: The unit of measurement of plane angle in the SI system of units. One radian encloses an arc on a concentric circle equal to the radius of a the circle.

Related terms:

For a list of other related terms see: angle

Symbol: rad

SI units: 1 radian = 1 cycle / 2π

Remarks:

There are 2π radians in a complete circle.

2π radians = 360 degrees.

radiance

Category: vector quantity

Definition: The radiant intensity in a specified direction, per unit of projected area.

Related terms: illuminance, irradiance, luminance

Symbol: L

SI units: not applicable

Remarks:

radiant energy

Category: scalar quantity

Definition: Energy in the form of electromagnetic radiation.

Related terms: none

Symbol: ??

SI units: joules = newton × meters

Remarks:

radiant exitance
radiant emittance

Category: scalar quantity

Definition: The radiant flux leaving a given surface per unit of area.

Related terms: irradiance

For a list of other related terms see: radiant flux

Symbol: M

SI units: watts / meter² = newtons / meter × second

Category: phenomenon

Definition: A scattering effect in which the electromagnetic radiation scattered from molecules differs in wavelength from the incident electromagnetic radiation.

Related terms:

For a list of other related terms see: scattering

Symbol: not applicable

SI units: not applicable

Remarks:

The changes in wavelength of the electromagnetic radiation correspond to specific energy-level differences in the molecules associated with rotation and vibration.

range

Category: common term

Definition: The distance, area, or volume affected, covered, included, or used.

Related terms: none

Symbol: not applicable

SI units: varies

Remarks:

rate
rate of flow

Category: scalar quantity

Definition: The amount of a quantity per unit of time.

Related terms: rate of change

Symbol: varies

SI units: varies

Remarks:

Examples:

quantity	units of the rate
angular velocity	radians / second
electric current	amperes
heat transfer	joules / second
linear acceleration	radians / second²
speed	meters / second
volumetric flow	meters³ / second

rate of change

Category: scalar quantity

Definition: The ratio of the change in one quantity to the change in another quantity over the same interval.

Related terms: rate

Symbol: varies

SI units: varies

Remarks:

Examples:

If quantity x changes by an amount Δx in a time Δt, then the rate of change of quantity x is Δx / Δt.

rational number

Category: concept

Definition: A number that is equal to the ratio of two integers.

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

Rational numbers are a superset of the integers and a subset of the real numbers.

ray

Category: concept

Definition: An infinitely narrow beam of wave motion.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

A ray of light corresponds to the path that a photon takes.

A ray is perpendicular to the wavefront.

Rayleigh scattering

Category: phenomenon

Definition: The scattering of electromagnetic radiation by particles that are small compared with the wavelength of the electromagnetic radiation.

Related terms:

For a list of other related terms see: scattering

Symbol: not applicable

SI units: not applicable

Remarks:

reactance

Category: scalar quantity

Definition: That part of impedance that is not due to resistance.

Related terms: electric reactance, mechanical reactance

Symbol: X

SI units: varies

Remarks:

reaction

Category: phenomenon

Definition: An interaction in which the interacting matter is modified.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

real number

Category: concept

Definition: A number that has no imaginary part.

Related terms:

For a list of other related terms see: number

Symbol: ??

SI units: not applicable

Remarks:

Real numbers are the union of the rational numbers and the irrational numbers, and a subset of the complex numbers.

recombination

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

rectilinear

Category: concept

Definition: Along a straight line.

Related terms: rectilinear motion

Symbol: not applicable

SI units: not applicable

Remarks:

rectilinear motion
linear motion
translational motion

Category: phenomenon

Definition: The motion of an object or reference frame that is moving in a straight line in an inertial reference frame. The object or reference frame may be accelerating but not rotating.

Related terms:

For a list of other related terms see: motion.

Symbol: not applicable

SI units: not applicable

Remarks:

red shift

Category: phenomenon

Definition: A shift in the wavelength of electromagnetic radiation toward longer wavelengths.

Related terms: Doppler effect, blueshift

Symbol: not applicable

SI units: hertz = cycles / second

Remarks:

Redshift can be measured from the displacement of spectral lines.

Redshift in electromagnetic radiation from nearby objects is due primarily to their motion away from the earth.

Redshift in electromagnetic radiation from distant objects is thought to be due primarily to the expansion of space.

reduced mass

Category: scalar quantity

Definition: The product of two masses divided by their sum.

Related terms: none

Symbol: ??

SI units: kilograms

Remarks:

Reduced mass may be calculated from the following mathematical expression:

reference frame

Category: concept

Definition: A reference frame consists of a three-dimensional coordinate system and coordinated clocks by which an observer at rest in the reference frame can determine the position and time at which an event occurs.

Symbol: not applicable

SI units: not applicable

Remarks:

A reference frame will be one of the following types:

inertial reference frame
accelerated reference frame

More than one reference frame may be considered in an experiment. The reference frames may have different origins, different orientations, and may be in motion with respect to each other.

For the special theory of relativity to hold, a reference frame must not be accelerated at any time during an experiment.

The special theory of relativity may hold if there are two reference frames and they are both accelerated and the accelerations are complementary i.e. the accelerations are equal in magnitude and opposite in direction.

In the general theory of relativity, reference frames may be accelerated.

reflectance

Category: scalar quantity

Definition: The ratio of the reflected radiant flux to the incident radiant flux.

Related terms:

For a list of other related terms see: radiant flux

Symbol: ρ

SI units: dimensionless

Remarks:

reflection

Category: phenomenon

Definition: The change in direction that a part of a ray of electromagnetic radiation undergoes when it encounters a surface between two media. The component of the incident velocity perpendicular to the surface is reversed.

Related terms: reflection laws.

Symbol: not applicable

SI units: not applicable

Remarks:

reflection laws
laws of reflection

Category: law

Statement: When electromagnetic radiation is reflected,

The incident ray, the normal to the surface at the point of incidence, and the reflected ray lie in the same plane.
The angle of incidence with the normal is equal to the angle of reflection with the normal.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

refraction

Category: phenomenon

Definition: The change in direction that a ray of electromagnetic radiation undergoes when it passes into a medium with a different index of refraction.

Related terms: none

Symbol: not applicable

SI units: radians

Remarks:

region
region of space

Category: concept

Definition: An extent that is distinguishable from its surroundings by some characteristic.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

relative

Category: common term

Definition:

An amount expressed in terms of a base amount.
The difference between a specified amount and a base amount
Orientation and position with respect to a base orientation and position.

Related terms: absolute

Symbol: not applicable

SI units: not applicable

Remarks:

relative atomic mass
atomic weight

Category: scalar quantity

Definition: The average mass of an atom of a chemical element expressed in atomic mass units.

Symbol: A_r

SI units: atomic mass units

Remarks:

It is necessary to say "average" because of the existence of isotopes of the element. The isotopes of an element have different atomic masses,

relative permeability

Category: scalar quantity

Definition: The ratio of the permeability of a medium to the permeability of free space.

Related terms: none

Symbol: ε_r

SI units: dimensionless

Remarks:

The mathematical expression for relative permeability is:

μ_r = μ / μ₀

where:

μ = permeability of the medium

relative permittivity
dielectric constant

Category: scalar quantity

Definition: The ratio of the permittivity of a dielectric medium to the permittivity of free space.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: μ_r

SI units: dimensionless

Remarks:

The mathematical expression for relative permittivity is:

ε_r = ε / ε₀

where:

ε = permittivity of the dielectric medium

relative velocity
relative motion

Category: vector quantity

Definition: The vector difference in velocity between two objects or reference frames.

Related terms:

For a list of other related terms see: motion.

Symbol: v

SI units: meters / second

Remarks:

The above definition can be used with accuracy only at velocities much less than the speed of light. It is not exact in that it does not take into account relativity. For example, if two observers are each traveling at (nearly) the speed of light in opposite directions, their relative velocity can not be two times the speed of light. Their relative velocity is, at most, the speed of light.

relativistic
nonrelativistic

Category: concept

Definition: Moving at a velocity such that there is a significant change in properties in accordance with the theory of relativity.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

relativistic dynamics

Category: branch of physics

Definition: The study of dynamics in which relativistic effects are significant.

Related terms:

For a list of other related terms see: dynamics

Symbol: not applicable

SI units: not applicable

Remarks:

relativistic kinetic energy

Category: scalar quantity

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: joules = newton × meters

Remarks:

relativistic mass

Category: scalar quantity

Definition: The mass of a object that is moving in the lab frame as measured in the lab frame.

Related terms: mass, rest mass

Symbol: m

SI units: kilograms

Remarks:

Relativistic mass is given by the mathematical expression:

m = γm₀

where:

m₀ = rest mass

relativistic matter

Category: concept

Definition: Matter that has a velocity in the reference frame of the observer that is a significant fraction of the speed of light.

Related terms:

For a list of other related terms see: theory of motion

Symbol: not applicable

SI units: not applicable

Remarks:

relativistic mechanics
nonrelativistic mechanics

Category: branch of physics

Definition: Mechanics that take relativity into account.

Related terms:

For a list of other related terms see: theory of motion

Symbol: not applicable

SI units: not applicable

Remarks:

relativistic quantum field theory
nonrelativistic quantum field theory

Category: theory

Definition: A quantum field theory mathematically expressed so as to be independent of a inertial reference frame.

Related terms:

For a list of other related terms see: quantum field theory

Symbol: not applicable

SI units: not applicable

Remarks:

relativistic quantum mechanics

Category: branch of physics

Definition: That branch of quantum mechanics that deals with the application of the quantum theory to particles moving at a velocity near to or equal to the velocity of light.

resonance

Category: phenomenon

Definition: The condition that exists when the frequency of a oscillating driving force coincides with the natural frequency of an oscillating system.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

resonances

Category: category of particle

Definition: Short-lived elementary particles that decay by strong interaction in about 10^-24 seconds.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Resonances can be regarded as excited states of more stable particles.

rest energy

Category: property

Definition: The energy equivalent of the rest mass of a particle.

Related terms: none

Symbol: ??

SI units: joules = newton × meters

Remarks:

rest mass

Category: scalar quantity

Definition: The mass of a object at rest in the lab frame.

Related terms: mass, relativistic mass

Symbol: m₀

SI units: kilograms

Remarks:

result of a mathematical operation

Category: mathematical expression

Definition: The number or mathematical expression that results when a mathematical operation is performed on an mathematical expression.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

resultant force

Category: vector quantity

Definition: Th net force that resuls from a combination of forces.

Related terms:

For a list of other related terms see: force

Symbol: F

SI units: newtons

Remarks:

retarded time

Category: scalar quantity

Definition: The time, in the lab frame, at which the electromagnetic radiation just received left its source

Related terms: none

Symbol: t_r

SI units: not applicable

Remarks:

The mathematical expression for retarded time is:

t_r = t - r / c

where:

t_r = retarded time

r = distance from the source to the observer at the time the electromagnetic radiation was emitted

t = time of arrival in the lab frame

revolution
revolve

Category: concept

Definition: A circular motion of a object about an exterior axis.

Related terms:

For a list of other related terms see: motion.

Symbol: not applicable

SI units: not applicable

Remarks:

The earth rotates on its axis once per day; it revolves around the sun once per year.

Reynolds number

Category: dimensionless number

Definition: A dimensionless number useful in characterizing fluid flow.

Related terms: none

Symbol: Re

SI units: dimensionless

Remarks:

Below a Reynold's number of about 2000, the flow of a fluid in a pipe is laminar; above about 2000, it is turbulent.

Riemannian geometry

Category: branch of mathematics

Definition: A non-Euclidean geometry in which the parallel postulate of Euclidean geometry is replaced by the postulate that through any point not on a given straight line, there is no straight line that is parallel to the given line.

Related terms: Euclidean geometry, Lobachevskian geometry.

Symbol: not applicable

SI units: not applicable

Remarks:

To be more precise, "straight line" should be replaced by "infinitely extended geodesic" in the above definition.

Riemannian geometry applies to, for example, a spherical surface.

right angle

Category: concept

Definition: An angle of 90º or ½π radians

Related terms: none

Symbol: ??

SI units: radians

Remarks:

right triangle

Category: concept

Definition: A triangle in which one of the angles is a right angle.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

right-hand rule
right-handed

Category: concept

Statement:

Hold the fingers of the right hand in the plane of rotation.
Bend the fingers in the direction of rotation.
The thumb then points in the positive direction.

Steps 2 and 3 may be reversed depending on what is known.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

If the above rule does not hold then the system is left-handed

rolling friction

Category: concept

Definition: The resistance to the rolling of a more or less circular object over a more or less plane surface.

Related terms:

For a list of other related terms see: friction

Symbol: not applicable

SI units: not applicable

Remarks:

root mean square
rms

Definition: The square root of the sum of the squares of a set of numbers.

Related terms: arithmetic mean, mode, median

Symbol: not applicable

SI units: not applicable

Remarks:

The root mean square of the numbers a₁ ,a₂ ,a₃ ,..., a_n is:

(a₁² + a₂² + a₃² + ... + a_n²)^1/2

rotating reference frame

Category: concept

Definition: A reference frame that is rotating.

Related terms: inertial reference frame

Symbol: not applicable

SI units: not applicable

Remarks:

The fact that a reference frame is rotating can be detected by an observer in the reference frame because of the forces generated by the rotation (cf. inertial reference frame).

rotation
rotational motion

Category: phenomenon

Definition: A circular motion of a object about an interior axis.

Related terms: revolution

For a list of other related terms see: motion.

Symbol: not applicable

SI units: not applicable

Remarks:

The earth rotates on its axis once per day; it revolves around the sun once per year.

Rutherford model

Category: hypothesis

Definition: A model of atoms that envision them as a nucleus surrounded by orbiting electrons.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The Rutherford model is sometimes described as a "planetary" model.

Rydberg constant

Category: empirical constant

Definition: A constant in the mathematical expression for the wave number of electromagnetic radiation emitted by atoms containing a single electron.

Related terms: none

Symbol: R

SI units: 1.097 373 153 4 × 10⁷ meter^-1

Remarks:

The mathematical expression for the wave number is:

where:

k = the wave number

R = the Rydberg constant

n = an integer

m = an integer > n

Z = the proton number (atomic number)

s

scalar
scalar quantity

Category: concept

Definition: A quantity that is defined by magnitude only. In contrast with a vector quantity, it does not have a direction associated with it.

Symbol: varies

SI units: not applicable

Remarks:

Examples:

Scalar quantities include: energy, mass, and time.

Vector quantities include: force, linear momentum, and velocity.

scalar component

Category: scalar quantity

Definition: Of a vector in a specified direction, a scalar equal to the magnitude of the projection of the vector on a line in the specified direction.

Related terms: component

Symbol: varies

SI units: not applicable

Remarks:

The mathematical expression for the scalar component of a vector in the direction of r is:

v_r = (v • r^) × r^

where:

v = specified vector

v_r = component of v in the direction of r

r^ = unit vector in the direction of r

Examples:

The scalar components of a position vector are simply equal to the coordinates of the position. In Cartesian coordinates:

r = r_x×i^ + r_y×j^ + r_z×k^

where:

r = position vector

r_x, r_y, r_z = scalar components = coordinates

i^, j^, k^ = unit vectors in x, y, z directions

scalar field

Category: concept

Definition: A field in which the field quantity is a scalar quantity.

Related terms:

For a list of other related terms see: field

Symbol: not applicable

SI units: not applicable

Remarks:

scalar function

Category: mathematical function

Definition: A mathematical function the value of which is a scalar quantity.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

scalar particle

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

scalar potential

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

scale factor

Category: number

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

Category: mathematical expression

Definition: The basic nonrelativistic equation of wave mechanics expressing the behavior of a particle in a force field.

Related terms: principal quantum number

Symbol: not applicable

SI units: not applicable

Remarks:

The time-dependent form of the equation, that describes progressive waves, applicable to the motion of free particles is:

where:

ψ = ψ(x,y,z,t) = wave function = probability amplitude

m = mass of particle

t = time

U = potential energy

The time-independent form of the equation, that describes standing waves, applicable to, for example, an electron in an atom is:

where:

ψ = ψ(x,y,z) = wave function

E = total energy

Schwarzschild radius

Category: scalar quantity

Definition: The critical radius to which matter must be compressed in order to form a black hole.

Related terms: event horizon

Symbol: ??

SI units: meters

Remarks:

The mathematical expression for the Schwarzschild radius is:

r = 2GM / c²

where::

r = Schwarzschild radius

M = the mass of the matter

Category: concept

Definition: Rules derived by quantum mechanics specifying the transitions that may occur between different quantum states of a system.

shear stress
shear

Category: vector quantity

Definition: The situation when shear stress is present is that an object has equal and opposite forces applied along parallel planes in the object.

The shear stress is the force per unit of area in a plane that is between and parallel to the two boundary planes.

Related terms: shear modulus, shear strain

For a list of other related terms see: stress

Symbol: τ

SI units: newtons / meter²

Remarks:

It is usually assumed that the force is evenly distributed over the planes. Otherwise, a smaller region must be considered.

shift

Category: common term

Definition: A change in frequency.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

SI prefixes

Category: concept

Definition: A set of prefixes for decimal multiples of units in the SI system of units.

Related terms: none

Symbol: see table

SI units: not applicable

Remarks:

The SI prefixes are:

prefix	symbol	exponent
yotta	Y	+24
zetta	Z	+21
exa	E	+18
peta	P	+15
tera	T	+12
giga	G	+9
mega	M	+6
kilo	k	+3
hecto	h	+2
deka	da	+1
deci	d	-1
centi	c	-2
milli	m	-3
micro	μ	-6
nano	n	-9
pico	p	-12
femto	f	-15
atto	a	-18
zepto	z	-21
yocto	y	-24

SI units
SI system of units
International System of Units
System International d'Unites

Category: system of units

Definition: The ISO has defined a system of units of measurement called the International System of Units. In French it is called System International d'Unites. The international abbreviation for this set of units is SI units.

The seven base units are:

base quantity	base unit
length	meter
mass	kilogram
time	second
electric current	ampere
thermodynamic temperature	kelvin
amount of substance	mole
luminous intensity	candela

Related terms:

For a list of other related terms see: systems of units

Symbol: see the specific unit

SI units: not applicable

Remarks:

Precise definitions of the seven base units in terms of actual physical measurements are specified by the ISO. These definitions may change from time to time.

Units of measurement for all other quantities are defined by the ISO in terms of the base units. These are called derived units.

The SI system of units is the modern equivalent of the metric system of units.

The SI system of units is sometimes called the "rationalized" MKS system of units.

sidereal time

Category: scalar quantity

Definition: Time based on successive transits of the March equinox across a given meridian.

Related terms: universal coordinated time

Symbol: ??

SI units: seconds

Remarks:

siemens

Definition: The unit of measurement of electric conductance in SI units.

Related terms: none

Symbol: S

SI units: 1 siemens = 1 ohm^-1 = 1 ampere / volt = 1 coulomb² / newton × meter × second

Remarks:

simple harmonic motion
SHM

Category: phenomenon

Definition: A periodic motion in which the displacement is a sinusoidal function of time.

Related terms:

For a list of other related terms see: motion.

Symbol: not applicable

SI units: not applicable

Remarks:

Simple harmonic motion results when a object is subjected to a restoring force directly proportional to the displacement from a fixed point in the line of motion.

The differential equation of simple harmonic motion is:

m = -kx

where:

m = mass of the object

= acceleration of the object

k = restoring force per unit of displacement

x = displacement

The solution to the differential equation is:

x = A cos(ωt + α)

where:

A = amplitude = maximum displacement

ω = angular frequency

t = time

α = phase angle

simultaneous
simultaneity

Category: concept

Definition: Two events are simultaneous in an inertial reference frame if, and only if, the time of their occurrence is the same as measured by coordinated clocks in the same inertial reference frame.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The same two events will generally not be simultaneous in another inertial reference frame.

Two events are simultaneous in all reference frames if they occur at the same time and (essentially) the same place.

sine
sine function

Category: mathematical function

Definition: One of the trigonometric functions. The ratio of the opposite side to the hypotenuse of a right triangle.

Related terms:

For a list of other related terms see: periodic functions

Symbol: sin

SI units: dimensionless

Remarks:

singularity

Category: concept

Definition: A point at which the derivative of a given mathematical function does not exist but every neighborhood of which contains points for which the derivative exists.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

sinusoidal

Category: concept

Definition: Having a waveform that is the same as that of a sine function.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

sinusoidal function

Category: mathematical function

Definition: A function in which the ordinates are proportional to a sine function.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Category: scalar quantity

Definition: Time based on successive transits of the sun across a given meridian.

Related terms: none

Symbol: ??

SI units: seconds

Remarks:

solid

Category: common term

Definition:

One of the three phases of matter (gas, liquid, solid).
A geometric element that has three dimensions and occupies space.
A substance that does not flow perceptibly under moderate stress.
A object that tends to maintain its shape and size when acted upon by a force.
A object with no internal cavity.

Related terms: none

Symbol: not applicable

SI units:

Remarks:

solid angle

Category: scalar quantity

Definition: The angular spread at the vertex of a cone or similar figure.

Related terms: none

Symbol: W

SI units: steradians

Remarks:

soliton

Category: particle

Definition: A solitary wave state with the properties of a stable particle.

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

source electric charge

Category: scalar quantity

Definition: An electric charge that is the source of a specific electric field.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: q

SI units: coulombs

Remarks:

This term is used in electrostatics.

space
spatial

Category: concept

Definition: A multi-dimensional extent in which objects exist and events occur and have position and direction.

Related terms: space-time, temporal, volume

Symbol: not applicable

SI units: meters³

Remarks:

In classical physics, the number of dimensions is three, all spatial.

In modern physics there are usually four dimensions, three spatial and one temporal.

In string theory a variety of number of dimensions has been contemplated, but in June 2001 the number is thought to be eleven.

space inversion
parity transformation

Category: mathematical operation

Definition: The simultaneous reversal of all spatial coordinates through the origin.

Related terms: inversion, space

For a list of other related terms see: parity

Symbol: P

SI units: not applicable

Remarks:

space parity

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

space quantization

Category: phenomenon

Definition: The limitation of the direction of the spin angular momentum to quantized values.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

space-time

Category: concept

Definition: The four-dimensional order in which the position of every event can be specified by three spatial coordinates and one temporal coordinate.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

space-time continuum

Category: concept

Definition: A four-dimensional coordinate system consisting of three spatial coordinates and one temporal coordinate by which the position of an event can be specified.

Related terms: 4-vector, 4-momentum

Symbol: not applicable

SI units: not applicable

Remarks:

In the space-time continuum a point is called an event.

The coordinates of an event are:

(ict, x, y, z)

where:

i =

t = time

The difference between two events is called an interval.

An interval is invariant under Lorentz transformation.

space-time invariance
space-time symmetry

Category: concept

Definition: Invariance under the following mathematical transformations:

change of reference frame
space inversion
space translation
time translation
...

Related terms: symmetry

Symbol: not applicable

SI units: not applicable

Remarks:

spatial coordinate

Category: ??

Definition: A coordinate that helps to define a position in space, not time.

Related terms:

For a list of other related terms see: coordinate systems

Symbol: varies (often x, y, z)

SI units: not applicable

Remarks:

special theory of relativity
Einstein's special theory of relativity

Category: theory

Definition: A theory of motion that deals with inertial reference frames.

Related terms: general theory of relativity

For a list of other related terms see: relativity

Symbol: not applicable

SI units: not applicable

Remarks:

The special theory of relativity was first published by Einstein in 1905.

What makes the special theory of relativity more general than the Newtonian theory of motion is that it takes into explicit account the time for information to propagate.

The special theory of relativity is based on these notions:

The laws of nature are the same for all observers.
The maximum speed of propagation is the speed of light
The speed of light is the same for all observers.
Reference frames are in uniform motion, cf. general theory of relativity.

specific

Category: common term

Definition: As a qualifying adjective to a quantity, the amount of the quantity per unit of mass.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

specific gravity
relative density

Category: property

Definition: The ratio of the density of a liquid to the density of water at the same temperature and pressure.

Related terms: none

Symbol: d

SI units: dimensionless

Remarks:

A specific gravity will usually be given for a standard temperature.

specific heat

Category: property

Definition: The amount of energy required to increase the temperature of a unit mass of substance one unit of temperature.

Symbol: c

SI units: not applicable

Remarks:

When not specifically qualified, specific heat usually means specific heat at constant pressure.

specific heat at constant pressure
specific heat capacity

Category: scalar quantity

Definition: The amount of energy required to increase the temperature of a unit mass of substance one unit of temperature while the pressure is held constant.

Symbol: c_p

SI units: joules / kilogram × kelvin = newton × meters / kilogram × kelvin

Remarks:

Category: scalar quantity

Definition: The rate of change of position.

The magnitude of a velocity irrespective of direction.

Related terms: none

Symbol: |v|

SI units: meters / second

Remarks:

speed of light
velocity of light

Category: scalar quantity

Definition: Unless otherwise qualified, the speed of light in a vacuum.

Related terms: none

Symbol: c

SI units: meters / second

Remarks:

The speed of light in a medium is always less than the speed of light in a vacuum.

speed of light in a vacuum
speed of light in vacuo

Category: fundamental constant

Definition: The speed at which electromagnetic radiation propagates in a vacuum.

Related terms: none

Symbol: c

Values: 2.997 924 58 × 10⁸ meters / second

Remarks:

The speed of light is the same in all inertial reference frames.

The speed of light decreases when the light enters a material medium.

spherical polar coordinate system
spherical polar coordinates

Category: concept

Definition: A coordinate system based on:

an origin
a plane though the origin
a base line in the plane through the origin
an axis perpendicular to the plane through the origin

The coordinates of a point, using the most common symbols, are:

r - the distance from the origin to the point
θ - the right-handed angle between the base line and a plane through the axis and the point
φ - the angle between the positive axis and a line connecting the origin and the point

Related terms:

For a list of other related terms see: coordinate systems

Symbol: not applicable

SI units: not applicable

Remarks:

Coordinates are stated in the following order (r,θ,φ).

Spherical polar coordinates are useful when the system has some degree of symmetry about the origin.

spherically symmetric

Category: quality

Definition: Symmetric about a point.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

spin
intrinsic angular momentum

Category: pseudovector quantity

Definition: That part of the angular momentum of a particle that is intrinsic to the particle.

For a list of other related terms see: angular momentum

Symbol: J

SI units: joule × seconds = newton × meter × seconds

Remarks:

The other component of the total angular momentum, orbital angular momentum is not included.

The mathematical expression for spin is of the form:

where:

s = spin quantum number

All particles are categorized either as bosons (obey Bose-Einstein statistics) or as fermions (obey Fermi-Dirac statistics) based on their spin:

fermions have odd half integer spin (1/2, 3 / 2,...).
bosons have integer spin (0, 1, 2, ...)

The following categories of particles have odd half integer spin and are therefore fermions:

leptons
baryons
quarks

The following categories of particles have integer spin and are therefore bosons:

mesons
gauge bosons

Spin should not be confused with isospin.

spin angular momentum

Category: pseudovector quantity

Definition:

On a macroscopic scale, spin angular momentum is the sum of the orbital angular momenta of the particles that make up a object and thus is not different in kind from orbital angular momentum.
On a microscopic scale, however, the spin of a particle, is different. For one thing, it is quantized. Therefore, in quantum mechanics the spin of a particle must also be taken into account when considering the total angular momentum of the particle.

Related terms:

For a list of other related terms see: angular momentum

Symbol: ??

SI units: kilogram × meters² / second

Remarks:

spin quantum number

Category: quantum number

Definition: A quantum number that characterizes the spin of a particle.

Related terms: spin

For a list of other related terms see: quantum number

Symbol: s, m_s, J, I

SI units: dimensionless

Remarks:

spin-statistics theorem

Category: theorem

Statement: Odd half integer spins can only be quantized consistently if they obey Fermi-Dirac statistics and integer spins can only be quantized consistently if they obey Bose-Einstein statistics.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

spinor

Category: concept

Definition: A mathematical function that transforms linearly under a proper Lorentz transformation.

This is a totally inadequate definition.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

square matrix

Category: mathematical expression

Definition: A matrix that has an equal number of rows and columns.

Related terms: none

Symbol: square array in brackets

SI units: not applicable

Remarks:

square wave

Category: concept

Definition: A waveform consisting of rectangular pulses with the pulse duration equal to the time between pulses.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

squark

Category: hypothetical particle

Definition: The supersymmetric partner of a quark.

Related terms:

For a list of other related terms see: supersymmetry

Symbol: ??

SI units: not applicable

Remarks:

stable equilibrium

Category: phenomenon

Definition: An equilibrium in which the system returns to its original state if is displaced slightly.

Related terms: unstable equilibrium

Symbol: not applicable

SI units: not applicable

Remarks:

standard
standardized

Category: common term

Definition: A value set by custom or authority as a rule for the measuring of extent or quantity

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

standard atmosphere

Category: arbitrary constant

Definition: A standard value of atmospheric pressure adopted by the ISO.

Related terms: standard pressure

Symbol: ??

SI units: 1 standard atmosphere = 101,325 newtons / meter²

Remarks:

standard deviation

Definition: The square root of the arithmetic mean of the squares of the deviations of all observations.

Related terms: mean, variance

Symbol: σ

SI units: not applicable

Remarks:

The mathematical expression for standard deviation is:

Standard deviation is a measure of the spread of the data about the arithmetic mean of the data.

standard pressure

Category: arbitrary constant

Definition: A standard value of pressure used for comparing quantities that are pressure dependent.

Related terms: standard atmosphere, standard temperature

Symbol: not applicable

Values: 10⁵ pascals = newtons / meter²

Remarks:

The value of the standard pressure has varied from time to time.

standard temperature

Category: arbitrary constant

Definition: A standard value of temperature used for comparing quantities that are pressure dependent.

Related terms: standard pressure

Symbol: not applicable

Value: 298.15 kelvin = 25 Celsius

Remarks:

Category: concept

Definition: A particular combination of the quantities associated with an system.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

static

Category: ??

Definition: Not changing or moving over a period of time.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

static friction

Category: vector quantity

Definition: The resistance opposing the motion of one surface over another before sliding occurs.

Related terms:

For a list of other related terms see: friction

Symbol:

SI units: newtons / meter²

Remarks:

statics

Category: branch of physics

Definition: That branch of mechanics that deals with a system of objects at rest relative to some given reference frame and with the forces between the objects.

Related terms: dynamics

Symbol: not applicable

SI units: not applicable

Remarks:

stationary

Category: concept

Definition:

Of a object, not moving.
Of a mathematical function, at a point such that the derivative is equal to zero.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

stationary state

Category: phenomenon

Definition: An energy state for which the probability of any observation is independent of time.

Related terms: quantum state

Symbol: not applicable

SI units: not applicable

Remarks:

stationary time principle
principle of stationary time

Category: principle

Statement: The path of a ray between two points during reflection or refraction is the path of least or greatest time.

Related terms: least time principle

Symbol: not applicable

SI units: not applicable

Remarks:

statistical mechanics

Category: branch of physics

Definition: That branch of physics that deals with the properties of macroscopic systems as predicted by the statistical behavior of their constituents.

Related terms:

For a list of other related terms see: branches of physics

Symbol: not applicable

SI units: not applicable

Remarks:

statistics

Category: concept

Definition:

A branch of mathematics.
A collection of quantitative data.
A probability distribution.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

steady state

Category: concept

Definition: A state of a system that is in equilibrium both internally and with its surroundings.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Stefan-Boltzmann constant

Category: fundamental constant

Definition: A constant in the Stefan-Boltzmann law.

Related terms: none

Symbol: σ

Values: 5.670 51 × 10^-8 watts / meter² × kelvin⁴

Remarks:

The Stefan-Boltzmann constant is a function other constants:

where:

k = Boltzmann constant

Stefan-Boltzmann law
Stefan-Boltzmann equation

Category: law

Statement: The power emitted by a black body per unit of surface area is proportional to the fourth power of the thermodynamic temperature of the black body.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of the Stefan-Boltzmann law is:

I = σT⁴

where:

I = power per unit of surface area

σ = Stefan-Boltzmann constant

T = thermodynamic temperature

steradian

Category: derived unit

Definition: The unit of measurement of solid angle in the SI system of units.

Related terms: none

Symbol: sr

SI units: steradians

Remarks:

A steradian is the solid angle that encloses an area on the surface of a sphere having its center at the vertex of the solid angle that is equal in area to a square with sides equal to the radius of the sphere.

The solid angle completely surrounding a point is 4π steradians.

stilb

Electricity and magnetism

Definition: A unit of measurement of luminance.

Related terms: none

Symbol: sb

SI units: 1 stilb = 1 candela / centi meter²

Remarks:

Stoke's theorem

Category: theorem

Statement: The integral of the curl of a vector function over a surface is equal to the integral of the vector function around the line that encloses the surface.

Related terms: divergence theorem

Symbol: not applicable

SI units: not applicable

Remarks:

The mathematical expression of Stoke's theorem is:

where:

v = vector

da = element of area

dl = element of length

straight line

Category: geometric element

Definition: A line such as would be generated by a point moving continuously in the same direction in a Cartesian space.

Related terms: geodesic

Symbol: not applicable

SI units: not applicable

Remarks:

strain

Category: scalar quantity

Definition: The change in length, volume, or shape of a object per unit of length, volume, or range affected due to applied stress.

Related terms: linear strain, shear strain, volume strain

For a list of other related terms see: stress

Symbol: ??

SI units: dimensionless

Remarks:

strange quark
strange antiquark

Category: elementary particle

Definition: One of the six flavors of quarks.

The properties of a strange quark are:

property	value
generation	2nd
bare mass	~150 MeV/c²
effective mass	~500 MeV/c²
electric charge	-1/3
spin	1/2
strangeness	+1

Related terms: strangeness

For a list of other related terms see: quarks

Symbol: s

SI units: not applicable

Remarks:

The strange quark has also been called the sideways quark.

strangeness

Category: quantized property

Definition: Strangeness is a quantized property and an additive quantum number associated with quarks.

Related terms:

For a list of other related terms see: quarks

Symbol: S

Values: -1, 0, or +1

Remarks:

By definition, strange quarks have a strangeness of +1, strange antiquarks have a strangeness of -1, and all other elementary particles have a strangeness of 0.

Strangeness is conserved in all particle interactions except weak interactions.

strength

Category: common term

Definition:

Intensity
The ability to exert a force.
The ability to supply energy.
The ability to resist stress.
The limit of the ability to exert a force.
The limit of the ability to supply energy.
The limit of the ability to resist stress.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

stress

Category: vector quantity

Definition: The resisting force per unit of area in a object or substance resulting from forces that tend to compress, elongate, or shear the object or substance.

Symbol: varies

SI units: pascals = newtons / meter²

Remarks:

Absent acceleration, the integral of the stress over a cross-section of the object will equal the applied external force.

A object may have internal stresses without any applied external force. In this case, the integral of the stress over a cross-section of the object will equal 0.

string

Category: hypothetical particle

Definition: A proposed ultimate elementary particle.

Related terms: string theory, superstring

Symbol: not applicable

SI units: not applicable

Remarks:

In some respects strings are similar to a "string" in the common meaning of the term. For example they could be open (have two ends) or closed (form a loop).

It is suggested that strings would have a size on the order of the Planck length (10^-35 meters). The Planck length is 10^-20 times smaller than a proton.

According to the string theory, all particles simply different modes of vibration of these strings.

string theory

Category: theory

Definition: A theory based on the concept that the ultimate elementary particles are string-like rather than point-like.

Related terms: string, superstring theory

Symbol: not applicable

SI units: not applicable

Remarks:

strong force
strong nuclear force
strong interaction force
color force

Category: fundamental force

Definition: A force between particles that possess color.

Related terms: strong interaction

For a list of other related terms see: force, interaction

Symbol: ??

SI units: newtons

Remarks:

The strong force is one of the four fundamental forces:

electromagnetic force
gravitational force
strong force
weak force

The particles that mediate the strong forces are called gluons.

The range of a strong force is very short: about 10^-15 meters.

The strong force is always attractive.

The strong force is the force that holds protons and neutrons together in the nuclei of atoms.

strong interaction

Category: concept

Definition: An interaction between particles arising as a consequence of their color charge.

Related terms: strong force

For a list of other related terms see: force, interaction

Symbol: not applicable

SI units: not applicable

Remarks:

It is thought that the strong interaction arises as the result the exchange of gluons between quarks and/or antiquarks as described by quantum chromodynamics.

Only particles that consist of quarks (ie; quarks and hadrons) participate in strong interactions. Leptons do not participate in strong interactions.

structure

Category: common term

Definition: The arrangement and interrelation of parts in a system.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

SU3

Category: concept

Definition: A mathematical group of importance in unitary symmetry.

Related terms: none

Symbol: SU3

SI units: not applicable

Remarks:

substance
material

Category: common term

Definition: Matter, usually in a macroscopic amount.

Related terms: matter, object

For a list of other related terms see: object

Symbol: not applicable

SI units: not applicable

Remarks:

A substance may or may not be homogeneous.

super conductivity

Category: phenomenon

Definition: A condition that occurs in certain substances when they are cooled below specific transition temperatures in which all resistance to the flow of electric current disappears.

Related terms: superfluidity

Symbol: not applicable

SI units: not applicable

Remarks:

supercooled

Category: phenomenon

Definition: Cooled below the temperature at which another phase would normally condense.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

A supercooled fluid is in a metastable state.

A supercooled state would usually arise because of a lack of sites for condensation to be initiated.

super fluidity

Category: phenomenon

Definition: A condition that occurs in certain fluids when they are cooled below specific transition temperatures in which all resistance to fluid flow disappears.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Superfluidity is attributed to Bose-Einstein condensation in which a large number of particles are in the lowest energy state.

superposition

Category: phenomenon

Definition: The quantity resulting from imposing two or more like quantities at a point or over an extent.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

In general, if the constituent phenomena are linear, then the resulting quantity will equal the sum of the imposed quantities.

superposition principle
principle of superposition

Category: principle

Statement: In any theory characterized by linear homogeneous differential equations, the sum of any number of solutions to the equations is also a solution.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

The interaction of two electric charges is not affected by the presence of other electric charges.

super string

Category: hypothetical particle

Definition: A superstring would be a string that has supersymmetry.

Related terms: superstring theory

Symbol: not applicable

SI units: not applicable

Remarks:

superstring theory

Category: theory

Definition: A string theory in which supersymmetry is taken into account.

Related terms: string, superstring

Symbol: not applicable

SI units: not applicable

Remarks:

super symmetry
SUSY

Category: theory

Definition: A theory based on the concept that every fermion has a corresponding boson and vice versa.

Related terms:

For a list of other related terms see: symmetry

Symbol: not applicable

SI units: not applicable

Remarks:

Names of supersymmetric particles:

Fermions:

fermion	supersymmetric partner
lepton	slepton
neutrino	sneutrino
quark	squark

Bosons

boson	supersymmetric partner
graviton	gravitino
Higgs boson	Higgsino
photon	photino
W boson	Wino
X boson	Xino
Y boson	Yino
Z boson	Zino

surface

Category: geometric element

Definition: A plane or curved two-dimensional locus of points.

Related terms: none

Symbol: &sigma

SI units: not applicable

Remarks:

surface charge density

Category: scalar quantity

Definition: The quantity of electric charge per unit of surface.

Related terms: none

Symbol: &sigma

SI units: coulombs / meter²

Remarks:

surface current
surface electric current

Category: vector quantity

Definition: An electric current on a surface.

For a list of other related terms see: electric current

Symbol: I

SI units: amperes = coulombs / second

Remarks:

surface current density

Category: vector quantity

Definition: The electric current per unit of distance perpendicular to the direction of motion.

Related terms: volume current density

For a list of other related terms see: electric current

Symbol: K

SI units: amperes / meter = coulombs / meter × second (for electric currents)

Remarks:

Surface current density is the relevant quantity when an electric current flows over a surface as opposed to through a volume (volume current density, J), or along a line (line current, I).

surface density

Category: scalar quantity

Definition: Of a quantity distributed on a surface, the amount of the quantity per unit area of surface.

Related terms: none

Symbol: Varies

SI units: Varies

Remarks:

surface tension

Category: vector quantity

Definition: A tension in the liquid at a surface between a liquid and a gas due to intermolecular forces.

Related terms: none

Symbol: σ

SI units: newtons / meter

Remarks:

surface wave

Category: phenomenon

Definition: A wave that travels along the boundary between two substances.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

susceptance

Category: scalar quantity

Definition: The reciprocal of reactance.

Related terms: electric susceptance

Symbol: B

SI units: siemens

Remarks:

susceptibility

Category: scalar quantity

Definition: See the related terms.

Symbol: c

SI units: not applicable

Remarks:

symbols

Atomic physics and nuclear physics

λ	decay constant
τ	mean lifetime
A	nucleon number
e	electron
E_B	binding energy
I	ionization potential
L	orbital angular momentum
n	neutron
n	principal quantum number
N	neutron number
p	proton
t₊	half-life
Z	proton number (atomic number)

Classical mechanics, periodic motion, and relativity

γ	Lorentz factor
μ	coefficient of friction
τ	proper time
ω	angular frequency
ω	angular velocity
a	acceleration
A	amplitude
E	energy
F	force
H	Hamiltonian function
I	moment of inertia
k	wave number
L	Lagrangian
m	mass
M	moment about a point
M	moment about an axis
P	power
p	pressure
p	generalized momentum
p	linear momentum
T	torque
T	kinetic energy
T	period
t	time
v	velocity
U	potential energy
W	work

constants:

α	fine structure constant
σ	Stefan-Boltzmann constant
u	atomic mass unit
μ	magneton
a₀	Bohr radius
c	speed of light
e	elementary charge
N_A	Avogadro constant
G	gravitational constant
h	Planck constant
k	Boltzmann constant
R	molar gas constant
R	Rydberg constant

ε	permittivity
λ	wavelength
μ	permeability
ρ	volume charge density
σ	surface charge density
σ	electric conductivity
σ	surface
υ	frequency
F	magnetic flux (F)
c	susceptibility
ψ	electric flux (ψ)
ξ	emf
A	magnetic vector potential
B	magnetic field
B	susceptance
C	electric capacitance
D	electric flux density
E	electric field strength
G	conductance
H	magnetic field strength
I	electric current
I	line current
J	volume current density
K	surface current density
L	electric inductance
m	dipole moment
m	magnetic moment
M	magnetization
p	electric dipole moment
p	polarization
P	electric polarization
q	electric charge
R	electric resistance
S	Poynting vector
Y	admittance
V	electric potential
Z	impedance

Mathematics

σ	standard deviation
W	solid angle
I	unit matrix
r	displacement
r	position vector

Particle physics:

γ	photon
μ	muon
ν	neutrino
σ	cross section
τ	tauon
B	baryon number
C	charge conjugation parity
e	elementary charge
e-	electron
e+	positron
I	isospin
s	spin quantum number
J	spin
l	lepton number
L	total angular momentum
I	orbital quantum number
m	mass
n	neutron
p	proton
P	parity
S	strangeness
s	spin quantum number
T	time reversal
W	W boson
Y	hypercharge
Z	Z boson

Quantum mechanics

ψ	wave function

Units of measurement:

A	ampere	electric current
b	barn	area
C	coulomb	electric charge
cd	candela	luminous intensity
F	farad	electric capacitance
H	henry	inductance
Hz	hertz	frequency
J	joule	energy
K	kelvin	thermodynamic temperature
kg	kilogram	mass
lm	lumen	luminous flux
lx	lux	illuminance
m	meter	length
mol	mole	amount of substance
N	newton	force
W	ohm	electric resistance
Pa	pascal	pressure
s	second	time
S	siemens	conductance
sb	stilb	luminance
T	tesla	magnetic flux density
V	volt	electric potential
W	watt	power
Wb	weber	magnetic flux

symmetric
asymmetric

Category: concept

Definition: Correspondence in size, shape, and relative position of parts on opposite sides of a central point, line, or plane.

Related terms: spherically symmetric

Symbol: not applicable

SI units: not applicable

Remarks:

symmetric matrix

Category: concept

Definition: A matrix that is equal to its own transpose.

M = M^T

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

symmetry breaking

Category: ??

Definition: (to be completed at a later time

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

symmetry operation

Category: mathematical operation

Definition: A mathematical operation on a system or object that leaves the system or object unchanged.

Related terms: conserved, invariant, Noether's theorem

Symbol: not applicable

SI units: not applicable

Remarks:

For each symmetry operation there is a conservation law that states that a particular quantity is conserved (Noether's theorem).

system

Category: common term

Definition: An interacting group of objects or particles that form an unified whole.

Related terms: closed system, open system, isolated system

For a list of other related terms see: object

Symbol: not applicable

SI units: not applicable

Remarks:

Everything else in the universe can be called the surroundings or the environment.

systems of units
systems of measurement

Category: concept

Definition: Any of a number of sets of units of measurement that can be used to specify amounts of quantities. Ideally, each set is based on a minimum set of base units from which all other units in the system are derived.

Related terms:

For a list of other related terms see: units of measurement

Symbol: not applicable

SI units: not applicable

Remarks:

The preferred system is the SI system of units.

The following systems of units have been or are used:

cgs system of units
cgs electrostatic system of units
cgs electromagnetic system of units
fps system of units
Gaussian system of units
Heaviside-Lorentz system of units
metric system of units
MKS system of units
SI system of units.

t

T invariance
T symmetry

Category: concept

Definition: Invariance under time reversal.

Related terms: CPT invariance

Symbol: not applicable

SI units: not applicable

Remarks:

tangent
tangent function

Category: concept

Definition:

One of the trigonometric functions. The ratio of the opposite side to the adjacent side of a right triangle.
Meeting, but not penetrating, a curve or surface at a point.

Related terms:

For a list of other related terms see: trigonometric functions

Symbol: tan

SI units: dimensionless

Remarks:

tauon
tau particle
normal tauon
antitauon

Category: elementary particle

Definition: A tauon is an elementary particle that is similar to an electron but with a mass that is 3491 times as great.

A normal tauon is a normal particle.

An antitauon is the antimatter equivalent of a tauon.

The properties of an normal tauon are:

property	value
electric charge	-1
rest mass	1784.1 MeV / c² = 3180.45 × 10^-30 kilogram
spin	1/2
mean lifetime	3.3 × 10^-13 seconds

Related terms: electron, muon

For a list of related terms see: lepton

Symbol: τ

SI units: not applicable

Remarks:

A tauon is a charged lepton.

Tauons belong to the third generation of leptons.

tauon neutrino
tauon antineutrino

Category: elementary particle

Definition: A tauon neutrino is a neutrino that belongs to the third generation of leptons.

The properties of an tauon neutrino are:

property	value
electric charge	0
rest mass	very small or 0
spin	1/2
mean lifetime	?? seconds

Related terms:

For a list of other related terms see: leptons

Symbol: ν_τ

SI units: not applicable

Remarks:

temperature

Category: scalar quantity

Definition: A measure of the kinetic energy of the particles that make up a object or substance.

Symbol: T

SI units: kelvin

Remarks:

The temperature of a object determines the direction of heat flow when the object is in thermal communication with another object.

temperature gradient

Category: vector quantity

Definition: The rate of change of temperature with respect to distance in a specified direction.

Related terms: none

Symbol: ??

SI units: kelvin / meter

Remarks:

temporal

Category: concept

Definition: Of, or relating to, time.

Related terms: space-time, spatial

Symbol: not applicable

SI units: not applicable

Remarks:

temporal coordinate

Category: concept

Definition: The coordinate that specifies a time, not a position in space.

Related terms:

For a list of other related terms see: coordinate systems

Symbol: t

SI units: not applicable

Remarks:

tensile strength

Category: scalar quantity

Definition: The ultimate strength of an object or substance under tension.

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

tension
tensile stress

Category: vector quantity

Definition: The stress in a object or substance caused by a force tending to elongate the object.

Related terms:

For a list of other related terms see: stress

Symbol: ??

SI units: newtons / meter²

Remarks:

tensor

Category: concept

Definition: A tensor is a generalized vector.

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

The term tensor is normally used only for tensors of order 2 or greater.

A tensor of order 0 is usually called a scalar.

A tensor of order 1 is usually called a vector.

In a space of d dimensions a tensor of order n has dⁿ components.

For example, in three-space:

a scalar has 3⁰ = 1 component

a vector has 3¹ = 3 components

a second order tensor has 3² = 9 components

In four-space:

a scalar has 4⁰ = 1 component

a vector has 4¹ = 4 components

a second order tensor has 4² = 16 components

tensor quantity

Category: concept

Definition: In a space having d dimensions, a quantity that has dⁿ components is called a tensor quantity of order n.

Related terms: none

Symbol: varies

SI units: not applicable

Remarks:

Usually we are dealing with a three-dimensional space, in which case a tensor quantity of order n has 3ⁿ components.

A tensor of order 0 is called a scalar.

A tensor of order 1 is called a vector.

A tensor or order 2+ is called a tensor.

terminal velocity

Category: vector quantity

Definition: The velocity with which a object moves with respect to a fluid when the resultant force is zero.

Related terms: none

Symbol: ??

SI units: meters / second

Remarks:

tesla

Definition: The unit of measurement of magnetic flux density in the SI system of units.

Related terms: none

Symbol: T

SI units: 1 tesla = 1 weber / meter² = 1 newton × second / coulomb × meter

Remarks:

test charge

Category: scalar quantity

Definition: An charge placed within a field for the purpose of measuring the field strength.

Related terms: source charge

For a list of other related terms see: electricity and magnetism

Symbol: Q

SI units: varies

Remarks:

The magnitude of the test charge must be small enough that it does not alter the strength of the field in which it is placed.

Examples:

An electric charge placed within an magnetic field for the purpose of measuring the magnetic flux density.

test mass

Category: scalar quantity

Definition: A mass placed within an gravitational field for the purpose of measuring the gravitational field strength.

Related terms: none

Symbol: Q

SI units: kilograms

Remarks:

The magnitude of the test mass must be small enough that it does not alter the gravitational field in which it is placed.

theorem

Category: generic term

Definition: A scientific proposition accepted or proposed as demonstrably true.

Related terms:

For a list of other related terms see: proposition

Symbol: not applicable

SI units: not applicable

Remarks:

A theorem is often a part of a general theory.

theoretical physics

Category: branch of physics

Definition: That branch of physics concerned primarily with the development of ideas, often through the use of mathematics, as opposed to observation and measurement.

Related terms: experimental physics

Symbol: not applicable

SI units: not applicable

Remarks:

Theoretical physics and experimental physics are complementary.

theory

Category: generic term

Definition: A set of scientific propositions that present a concise and systematic explanation of a set of related facts.

Related terms:

For a list of other related terms see: proposition

Symbol: not applicable

SI units: not applicable

Remarks:

In common usage, theory can also denote an unproved assumption.

theory of everything
TOE

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

A successful theory of everything should eliminate disparities between relativity and quantum theory.

theory of motion
laws of motion

Category: generic term

Definition: A theory of motion is a statement of the laws that govern the motion of objects.

Related terms:

For a list of other related terms see: Newton's laws of motion, relativity

Symbol: not applicable

SI units: not applicable

Remarks:

A given theory of motion may be valid only under certain simplifying assumptions.

theory of relativity
relativity theory

Category: theory

Definition: A theory that deals with the consequences of relative motion between reference frames.

Related terms:

For a list of other related terms see: relativity

Symbol: not applicable

SI units: not applicable

Remarks:

thermal

Category: common term

Definition: Of, relating to, or caused by internal energy.

Related terms: heat

Symbol: not applicable

SI units: not applicable

Remarks:

thermal conductance

Category: property

Definition: The heat flow per unit of time per unit of area per degree of temperature gradient.

Related terms: heat transfer coefficient

Symbol: K

SI units: watts / meter² × kelvin

Remarks:

thermal conductivity

Category: property

Definition: A property of a medium that is equal to the ratio of the rate of heat transfer by conduction to the temperature gradient in the substance.

Related terms:

For a list of other related terms see: conductivity

Symbol: λ

SI units: joules / second × meter × kelvin = newtons / second × kelvin

Remarks:

The mathematical expression for the rate of heat transfer is:

dQ/dt = λ A dT/dx

where:

Q = amount of heat transmitted

t = time

λ = thermal conductivity

A = cross-sectional area

T = temperature

x = distance in the direction of the temperature gradient

thermal radiation

Category: phenomenon

Definition: Electromagnetic radiation emitted by a substance the amount and quality of which depend only on the thermodynamic temperature of the substance.

Symbol: not applicable

SI units: not applicable

Remarks:

thermal resistance

Category: property

Definition: The reciprocal of the thermal conductance.

Related terms: none

Symbol: R

SI units: meters² × kelvin / watt

Remarks:

thermodynamic temperature
absolute temperature

Category: base quantity

Definition: The temperature of a substance measured from absolute zero.

Related terms: base quantities

Symbol: T

SI units: kelvin

Remarks:

Thermodynamic temperature is a base quantity in the SI system of units.

The thermodynamic temperature of a system is directly related to the thermal energy of the system.

thermodynamics

Category: branch of physics

Definition: That branch of physics that deals with the interrelation between heat, work, and internal energy.

Related terms:

For a list of other related terms see: branches of physics

Symbol: not applicable

SI units: not applicable

Remarks:

third component of isotopic spin

Category: vector quantity

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: ??

Remarks:

Thomson scattering

Category: phenomenon

Definition: The scattering of electromagnetic radiation by free or loosely bound electrons.

Related terms: scattering

Symbol: not applicable

SI units: not applicable

Remarks:

thought experiment

Category: concept

Definition: An "experiment" conducted entirely in the imagination.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

three object problem

Category: concept

Definition: The determination of the position and velocity of three objects in a mutual gravitational field.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

No analytical solution can be obtained except in special cases.

time

Category: base quantity

Definition: One of those fundamental quantities that can not be defined except in terms of other fundamental quantities. These are: force, length, mass, and time.

Related terms: base quantities, relativity

Symbol: t

SI units: seconds

Remarks:

Time is a base quantity in the SI system of units.

Time is the temporal component of the space-time continuum.

time integral

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

time interval

Category: scalar quantity

Definition: The separation in time between two events.

Related terms: interval

Symbol: Δt

SI units: seconds

Remarks:

time parity

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: T

SI units: not applicable

Remarks:

time reversal

Category: concept

Definition: Substitution of time -t for time t.

Related terms: T invariance

Symbol: T

SI units: not applicable

Remarks:

top quark
top antiquark

Category: elementary particle

Definition: One of the six flavors of quarks.

The properties of a bottom quark are:

property	value
generation	3rd
bare mass	> 23,000 MeV/c²
effective mass	> 23,000 MeV/c²
electric charge	+2/3
spin	1/2
truth	+1

Related terms: truth

For a list of other related terms see: quarks

Symbol: t

Values: -1, 0, or +1

Remarks:

The top quark has also been called the truth quark.

topological defect

Category: phenomenon

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

topological space

Category: ??

Definition: (to be completed at a later time)

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

topology

Category: mathematics

Definition: The study of the properties of geometric configurations that are unaltered if the configuration is subjected to any one-to-one mathematical transformation that is continuous in both directions.

Related terms: none

Symbol: not applicable

SI units: not applicable

Definition: The sum of the elements on the main diagonal of a matrix.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

transient

Category: concept

Definition: Occurring or passing through in a short time interval.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

translation

Category: ??

Definition: The movement of a object or system in such a way that all points are moved in parallel directions and equal distances.

Related terms: motion

Symbol: not applicable

SI units: not applicable

Remarks:

translational kinetic energy

Category: scalar quantity

Definition: That portion of the kinetic energy of an object that is due to translational motion.

Related terms: none

Symbol: KE

SI units: joules = newton × meters

Remarks:

transmission
transfer

Category: phenomenon

Definition: The passage of a quantity such as electromagnetic radiation, energy, force, heat, mass, or volume, through a surface, space, medium, or device or between objects.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Transmission implies passage through a medium, while transfer implies passage between objects.

transpose of a matrix

Electromagnetic radiation.

Definition: The matrix formed by interchanging the rows and columns of a given matrix.

Related terms: none

Symbol: M^Twhere M is the original matrix

SI units: not applicable

Remarks:

transverse wave
S-wave

Category: concept

Definition: A wave in which the displacement of the transmitting medium is perpendicular to the direction of propagation.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

Examples:

traveling wave

Category: phenomenon

Definition: A waveform that moves through space.

Related terms: standing wave

Symbol: not applicable

SI units: not applicable

Remarks:

trigonometric function

Category: generic term

Definition: A mathematical function of an angle. The value of the function can be expressed in terms of the ratios of the sides of a right triangle, however a trigonometric function applies to an angle of any size in any circumstance.

Related terms: sine, cosine, periodic functions, tangent

Symbol: sin/cos/tan

SI units: not applicable

Remarks:

The right triangle referred to can be described as follows:

consider an angle that is formed by two lines
position the vertex of the angle at the origin
let one of the lines lie along the positive x-axis
orient the second line so that the desired angle is measured in a counter-clockwise direction
draw a vertical line intersecting the second line and forming a right triangle between the x-axis, the second line, and the vertical line

The sides of the right triangle are referred to as follows:

The side formed by the x-axis is called the adjacent side.
The side formed by the vertical line is called the opposite side.
The side formed by the second line is called the hypotenuse.

triple point

Category: property

Definition: The pressure and temperature at which the three phases of a substance (vapor, liquid, solid) are present and in equilibrium.

Related terms: none

Symbol: not applicable

SI units: pascals = newtons / meter² × kelvin

Remarks:

tritium

Category: chemical element

Definition: The isotope of hydrogen that has two neutrons in the nucleus.

Related terms: deuterium

Symbol: T

SI units: not applicable

Remarks:

truth
topness

Category: quantum number

Definition: Truth is a quantized property and an additive quantum number associated with quarks.

Related terms: none

Symbol: t

Values: -1, 0, or +1

Remarks:

By definition, truth quarks have a truth of +1, truth antiquarks have a truth of -1, and all other elementary particles have a truth of 0.

Truth is conserved in all interactions except weak interactions.

tunneling
quantum tunneling

Category: phenomenon

Definition: The movement of a particle through a barrier that, in classical mechanical theory, the particle has insufficient energy to surmount.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

This phenomenon is explained by the probability distribution of the particle that, though perhaps very small, is nevertheless non-zero at a point outside the barrier.

turbulence

Category: phenomenon

Definition: Motion of a fluid in which the velocity of the fluid at any point may vary with time in both magnitude and direction.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

turbulent flow

Category: phenomenon

Definition: Fluid flow that is characterized by random motions.

Related terms: laminar flow, Reynolds number

Category: phenomenon

Definition: An object or reference frame is in uniform motion if it is neither accelerating or rotating.

Related terms:

For a list of other related terms see: motion.

Symbol: not applicable

SI units: not applicable

Remarks:

uniform rotational motion

Category: phenomenon

Definition: A rotating object of reference frame is in uniform rotational motion if the rate of rotation is not changing.

Related terms: uniform translational motion

For a list of other related terms see: motion.

Symbol: not applicable

SI units: not applicable

Remarks:

uniformly accelerated motion

Category: phenomenon

Definition: Motion of a object when its acceleration is constant and the motion is in a straight line.

Symbol: not applicable

SI units: not applicable

Remarks:

uniformly accelerated rotation

Category: concept

Definition: A rotating motion that is accelerating at a constant rate.

Related terms: uniformly accelerated motion

Symbol: not applicable

SI units: not applicable

Remarks:

unit

Category: common term

Definition:

An amount of a quantity adopted as a basis of measurement.
Equal to one in amount or number.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

unit matrix
identity matrix

Category: mathematical expression

Definition: A square matrix in which all of the elements on the main diagonal have a value of 1 and all other elements have a value of 0.

Related terms: main diagonal, matrix

Symbol: I

SI units: not applicable

Remarks:

An unit matrix is the matrix equivalent of the scalar 1.

A unit matrix can be of any order (number of rows and columns)

Examples:

The following is an unit matrix of order 3:

unit of measurement

Category: concept

Definition: A standardized and named amount of a physical quantity by which an amount of the quantity can be specified by a number and the name of the quantity.

Related terms: SI units

Symbol: not applicable

SI units: not applicable

Remarks:

unit vector

Category: concept

Definition: A vector with a unit length and a specified direction.

Related terms: none

Symbol: varies

SI units: not applicable

Remarks:

Examples:

The following symbols are commonly used for unit vectors in the direction of the axes of a Cartesian coordinate system:

i^ in the x direction

j^ in the y direction

k^ in the z direction

unit volume

Category: One unit of volume.

Definition: (to be completed at a later time)

Related terms: none

Symbol: ??

SI units: meters³

Remarks:

Examples:

1 cubic meter
1 cubic centimeter
1 liter

Remarks:

universal coordinated time
Greenwich mean time
Zulu time

Category: ??

Definition: The arithmetic mean of the times kept by a set of atomic clocks maintained by the US Naval Observatory.

Related terms: none

Symbol: Z

SI units: not applicable

Remarks:

universe
nature
reality

Category: phenomenon

Definition: The whole of phenomena that can be observed or potentially observed directly or indirectly.

Related terms: science, philosophy

Symbol: not applicable

SI units: not applicable

Remarks:

unstable equilibrium

Category: phenomenon

Definition: An equilibrium in which the system moves even farther from its original state if is displaced slightly.

Related terms: metastable, stable equilibrium

Symbol: not applicable

SI units: not applicable

Remarks:

up quark
up antiquark

Category: elementary particle

Definition: One of the six flavors of quarks.

The properties of an up quark are:

property	value
generation	1st
bare mass	~4.2 MeV/c²
effective mass	~350 MeV/c²
electric charge	+2/3
spin	1/2
upness	+1

Related terms: upness

For a list of other related terms see: quarks

Symbol: u

SI units: not applicable

Remarks:

upness

Category: quantized property

Definition: Upness is a quantized property and an additive quantum number associated with quarks.

Related terms:

Definition: The amount, number, or extent of a specified quantity or property.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

vapor

Category: concept

Definition: A gas below its critical temperature.

Related terms: none

Symbol: not applicable

SI units: not applicable

Remarks:

A gas below its critical temperature can be changed to a liquid by increasing the pressure while maintaining a constant temperature. A gas above its critical temperature can not be liquefied without reducing the temperature.

vapor pressure

Category: property

Definition: Vapor pressure is a property of a liquid. It is the pressure that would exist if a vapor phase were present and in equilibrium with the liquid.

Related terms: none

Symbol: p

SI units: pascals = newtons / meter²

Remarks:

The vapor pressure of a liquid is dependent on its temperature.

variable

Category: mathematical expression

Definition: A symbol representing a quantity, or the quantity itself, that may take any one of a set of values.

Symbol: varies

SI units: varies

Remarks:

variance

Definition: The square of the standard deviation.

Related terms: mean

Symbol: not applicable

SI units: not applicable

Remarks:

vector
vector quantity
first order tensor
polar vector

Category: concept

Definition: A quantity that has both magnitude and direction.

Symbol: bold letter

SI units: varies

Remarks:

An example of a vector quantity is the wind in the earth's atmosphere.

A vector is a tensor of order 1.

In order to be a true vector (cf. pseudovector), the vector must be invariant under any coordinate transformation .

A vector quantity is said to have a component in each direction.

In Cartesian coordinates:

v = v_xi^ + v_yj^ + v_zk^

By the Pythagorean theorem

v_m = |v| = (v_x² + v_y² + v_z²)^1/2

where:

v_m is the magnitude.

v is the vector quantity.

v_x is the scalar component in the x direction

v_y is the scalar component in the y direction

v_z is the scalar component in the z direction

A vector can be expressed as the product of its magnitude and a unit vector in the direction of the vector:

v = v × r

where:

v = a vector

v = magnitude of the vector

r = unit vector in direction of the vector

vector field

Category: concept

Category: vector quantity

Definition: The speed and direction of motion of an object in motion.

Related terms: angular velocity, speed

Symbol: v

SI units: meters / second

Remarks:

DE × Dt £ h / 4π.

virtual photon

Category: particle

Definition: A short-lived photon that carries energy and momentum between two electrically charged particles that are involved in an interaction (collision).

Related terms: none

Symbol: ??

SI units: not applicable

Remarks:

The virtual photon is said to mediate the electromagnetic force.

viscosity
dynamic viscosity

Category: property

Definition: The property of fluids by which they offer a resistance to flow in laminar flow.

Symbol: η

SI units: poise = pascal × seconds = newton × seconds / meter²

Remarks:

The viscosity of a liquid usually decreases with temperature, but the viscosity of a gas increases with temperature.

volt

Definition: The unit of measurement of electric potential in the SI system of units.

Related terms:

For a list of other related terms see: electricity and magnetism

Symbol: V

SI units: 1 volt = 1 joule / coulomb = 1 newton × meter / coulomb

Remarks:

volume

Category: pseudoscalar quantity

Definition: An amount of space.

Related terms: none

Symbol: V

SI units: meters³

Remarks:

volume charge density

Category: scalar quantity

Definition: The amount of electric charge per unit of volume.

Related terms: none

Symbol: &rho

SI units: coulombs / meter³

Remarks:

volume current
volume electric current

Category: vector quantity

Definition: An electric current flowing through a volume.

Symbol: I

SI units: amperes = coulombs / second

Remarks:

volume current density

Category: vector quantity

Definition: The electric current per unit of area perpendicular to the direction of motion.

Related terms: surface current density

For a list of other related terms see: electric current

Symbol: J

SI units: amperes / meter² = coulombs / meter × second

Remarks:

Volume current density is the relevant quantity when an electric current flows through a volume as opposed to over a surface (surface current density), or along a line (line current).

volume strain
bulk strain

Category: scalar quantity

Definition: The change in volume per unit of volume when pressure is applied to all sides of a object or substance.

Related terms: bulk modulus

For a list of other related terms see: stress

Symbol: ??

SI units: dimensionless

Remarks:

w

W boson
W particle

See specific term: W+ boson, W- boson

W⁺ boson
W⁺ particle

Category: elementary particle

Definition: A gauge boson that mediates certain types of weak interactions.

The properties of a W+ boson are:

property	value
electric charge	+1
rest mass	81,800 MeV / c² = ?? × 10^-30 kilogram
spin	1
mean lifetime	unknown

Related terms: intermediate vector boson, W- boson, Z boson

Symbol: W⁺

SI units: not applicable

Remarks:

W^- boson
W^- particle

Category: elementary particle

Definition: A gauge boson that mediates certain types of weak interactions.

The properties of a W- boson are:

property	value
electric charge	-1
rest mass	81,800 MeV / c² = ?? × 10^-30 kilogram
spin	1
mean lifetime	unknown

Related terms: intermediate vector boson, W+ boson, Z boson

Symbol: W^-

SI units: not applicable

Remarks:

watt