This glossary of physics is a list of definitions
of terms and concepts relevant to physics,
its sub-disciplines, and related fields, including
mechanics, materials science, nuclear physics,
particle physics, and thermodynamics.
For more inclusive glossaries concerning related
fields of science and technology, see Glossary
of chemistry terms, Glossary of astronomy,
Glossary of areas of mathematics, and Glossary
of engineering.
== A ==
ab initio
A mathematical model which seeks to describe
atomic nuclei by solving the non-relativistic
Schrödinger equation for all constituent
nucleons and the forces that exist between
them. Such methods yield precise results for
very light nuclei but become more approximate
for heavier nuclei.
Abbe number
Also called the V-number or constringence.
In optics and lens design, a measure of a
transparent material's dispersion (a variation
of refractive index versus wavelength). High
values of V indicate low dispersion.
absolute electrode potential
In electrochemistry, the electrode potential
of a metal measured with respect to a universal
reference system (without any additional metal–solution
interface).
absolute humidity
The ratio of the water vapor in a sample of
air to the volume of the sample.
absolute magnitude
Is a measure of the luminosity of a celestial
object, on a logarithmic astronomical magnitude
scale. An object's absolute magnitude is defined
to be equal to the apparent magnitude that
the object would have if it were viewed from
a distance of exactly 10 parsecs (32.6 light-years),
with no extinction (or dimming) of its light
due to absorption by interstellar dust particles.
absolute motion
absolute pressure
Is zero-referenced against a perfect vacuum,
using an absolute scale, so it is equal to
gauge pressure plus atmospheric pressure.
absolute scale
Is a system of measurement that begins at
a minimum, or zero point, and progresses in
only one direction. An absolute scale differs
from an arbitrary, or "relative," scale, which
begins at some point selected by a person
and can progress in both directions. An absolute
scale begins at a natural minimum, leaving
only one direction in which to progress.
absolute zero
The theoretical lowest possible temperature,
understood by international agreement as equivalent
to 0 Kelvin or −273.15 °C (−459.67 °F).
More formally, it is the theoretical lower
limit of the thermodynamic temperature scale,
at which enthalpy and entropy of a cooled
ideal gas reach their minimum values and the
fundamental particles of nature have minimal
vibrational motion.
absorption spectroscopy
Refers to spectroscopic techniques that measure
the absorption of radiation, as a function
of frequency or wavelength, due to its interaction
with a sample. The sample absorbs energy,
i.e., photons, from the radiating field. The
intensity of the absorption varies as a function
of frequency, and this variation is the absorption
spectrum. Absorption spectroscopy is performed
across the electromagnetic spectrum.
absorptivity
accelerating expansion of the universe
Is the observation that the expansion of the
universe is such that the velocity at which
a distant galaxy is receding from the observer
is continuously increasing with time.
acceleration
The rate at which the velocity of a body changes
with time.
acceleration due to gravity
The acceleration on an object caused by the
force of gravitation.
accelerometer
An instrument used to measure the proper acceleration
of a body irrespective of other forces.
acoustics
The branch of physics dealing with the production,
transmission and effects of sound.
adhesion
The tendency of dissimilar particles or surfaces
to cling to one another. Contrast cohesion.
adiabatic cooling
adiabatic heating
aerodynamics
Is the study of the motion of air, particularly
its interaction with a solid object, such
as an airplane wing. It is a sub-field of
fluid dynamics and gas dynamics, and many
aspects of aerodynamics theory are common
to these fields.
afocal system
air mass
air mass (astronomy)
air mass (solar energy)
albedo
The fraction of the total light incident on
a reflecting surface, especially a celestial
body, which is reflected back in all directions.
alloy
A chemical mixture of a metal with one or
more other metals or other elements.
alpha decay
alpha particle (α)
Also symbolized by α2+, He2+, and 42He2+.
A type of subatomic particle consisting of
two protons and two neutrons bound together
into a particle identical to the nucleus of
a helium-4 ion. Alpha particles are classically
produced in the process of radioactive alpha
decay, but may also be produced in other ways
and given the same name.
alternating current (AC)
A form of electric current in which the movement
of electric charge periodically reverses direction.
Contrast direct current.
ammeter
An instrument that is used to measure electric
current.
amorphous solid
A type of solid which does not have a definite
geometrical shape. Or its non-crystalline
solid.
ampere (A)
Often abbreviated as amp.
The SI base unit of electric current, defined
as one coulomb of electric charge per second.
amplifier
amplitude
The height of a wave measured from its center
(normal) position.
angle of incidence
angle of reflection
ångström (Å)
A unit of length primarily used to measure
subatomic particles that is equal to 10-10
meters (one ten-billionth of a meter) or 0.1
nanometers.
angular acceleration
angular displacement
angular frequency
angular momentum
angular velocity
anion
A negatively charged ion. Contrast cation.
annihilation
anode
The electrode through which a conventional
electric current flows into a polarized electrical
device; the direction of current flow is,
by convention, opposite to the direction of
electron flow, and so electrons flow out of
the anode. In a galvanic cell, the anode is
the negative terminal or pole which emits
electrons toward the external part of an electrical
circuit. However, in an electrolytic cell,
the anode is the wire or plate having excess
positive charge, so named because negatively
charged anions tend to move towards it. Contrast
cathode.
antigravity
antimatter
antineutron
antiparticle
antiproton
antiquark
arc length
Archimedes' principle
area moment of inertia
astronomical unit
astrophysics
The branch of astronomy that deals with the
physics of the Universe, especially with the
nature of celestial bodies rather than their
positions or motions in space.
attenuation coefficient
atom
A basic unit of matter that consists of a
dense central nucleus surrounded by a cloud
of negatively charged electrons. The atomic
nucleus contains a mix of positively charged
protons and electrically neutral neutrons.
atomic line filter
atomic mass
atomic mass unit
One-twelfth the mass of an atom of the isotope
126C.
atomic number (Z)
The number of protons found in the nucleus
of an atom. It is most often used to classify
elements within the periodic table.
atomic orbital
atomic packing factor
atomic physics
A branch of physics that studies atoms as
isolated systems of electrons and an atomic
nucleus. Compare nuclear physics.
atomic structure
atomic weight (A)
The sum total of protons (or electrons) and
neutrons within an atom.
audio frequency
average speed
Avogadro constant
(6.02214086 × 1023 mol−1) In chemistry
and physics, the Avogadro constant (named
after the scientist Amedeo Avogadro) is the
number of constituent particles, usually atoms
or molecules, that are contained in the amount
of substance given by one mole.
Avogadro's law
A physical law which states that volumes of
gases which are equal to each other at the
same temperature and pressure will contain
equal numbers of molecules.
Avogadro's number
The number of molecules in exactly 12g of
carbon-12, equaling 6.022 x 1023.
axion
A hypothetical subatomic particle postulated
to account for the rarity of processes that
break charge-parity symmetry. It is very light,
electrically neutral, and pseudoscalar.
azimuthal quantum number
== B ==
Babinet's principle
A theorem concerning diffraction which states
that the diffraction pattern from an opaque
body is identical to that from a hole of the
same size and shape except for the overall
forward beam intensity.
background radiation
The ubiquitous ionising radiation to which
the general population is exposed.
ballistics
Balmer series
barometer
A scientific instrument used in meteorology
to measure atmospheric pressure. Pressure
tendency can forecast short-term changes in
the weather.
baryon
battery
A combination of two or more electrical cells
which produces electricity.
beam
A structural element that is capable of withstanding
load primarily by resisting bending.Beams
are traditionally descriptions of building
or civil engineering structural elements,
but smaller structures such as truck or automobile
frames, machine frames, and other mechanical
or structural systems contain beam structures
that are designed and analyzed in a similar
fashion.
bending
Also known as flexure.
The behavior of a slender structural element
subjected to an external load applied perpendicularly
to a longitudinal axis of the element.
bending moment
Bernoulli equation
Bernoulli's principle
Bessel function
beta decay
beta particle
A high-energy, high-speed electron or positron
emitted by certain types of radioactive atomic
nuclei.
Big Bang
The prevailing cosmological model that describes
the early development of the Universe.
binding energy
The mechanical energy required to disassemble
a whole into separate parts. A bound system
typically has a lower potential energy than
the sum of its constituent parts.
binomial random variable
biocatalysis
biophysics
An interdisciplinary science using methods
of and theories from physics to study biological
systems.
black body
A hypothetical idealized physical body that
completely absorbs all incident electromagnetic
radiation, regardless of frequency or angle
of incidence. Perfect black bodies are imagined
as substitutes for actual physical bodies
in many theoretical discussions of thermodynamics,
and the construction of nearly perfect black
bodies in the real world remains a topic of
interest for materials engineers. Contrast
white body.
black-body radiation
The type of electromagnetic radiation within
or surrounding a body in thermodynamic equilibrium
with its environment, or emitted by a black
body (an opaque and non-reflective body) held
at constant, uniform temperature. The radiation
has a specific spectrum and intensity that
depends only on the temperature of the body.
block and tackle
A system of two or more pulleys with a rope
or cable threaded between them, usually used
to lift or pull heavy loads.
Bohr model
boiling point
The temperature at which a liquid undergoes
a phase change into a gas; the vapour pressure
of liquid and gas are equal at this temperature.
boiling point elevation
Boltzmann constant
A physical constant relating the average kinetic
energy of the particles in a gas with the
temperature of the gas. It is the gas constant
R divided by the Avogadro constant NA.
Bose–Einstein condensate (BEC)
boson
A type of particle that behaves according
to Bose–Einstein statistics and possesses
integer spin. Bosons include elementary particles
such as photons, gluons, W and Z bosons, Higgs
bosons, and the hypothetical graviton, as
well as certain composite particles such as
mesons and stable nuclides of even mass number.
Bosons constitute one of two main classes
of particles, the other being fermions. Unlike
fermions, there is no limit to the number
of bosons that can occupy the same quantum
state.
Boyle's law
The volume of a given mass of a gas at constant
temperature is inversely proportional to the
pressure.
Bra–ket notation
Bragg's law
bremsstrahlung
Radiation emitted by the acceleration of unbound
charged particles.
Brewster's angle
british thermal unit (btu)
An Imperial unit of energy defined as the
amount of energy needed to heat one pound
of water by one degree Fahrenheit; 1 btu is
equal to about 1055 joules. In scientific
contexts the btu has largely been replaced
by the SI unit of energy, the joule.
brittleness
The tendency of a material to break without
significant plastic deformation when subjected
to stress. Brittle materials absorb relatively
little energy prior to fracture, even those
of high strength. Breaking is often accompanied
by a snapping sound.
Brownian motion
Also called pedesis.
The presumably random movement of particles
suspended in a fluid (liquid or gas) resulting
from their bombardment by the fast-moving
atoms or molecules in the gas or liquid.
Bulk modulus
A measure of a substance's resistance to uniform
compression defined as the ratio of the infinitesimal
pressure increase to the resulting relative
decrease of the volume. Its base unit is the
pascal.
buoyancy
An upward force exerted by a fluid that opposes
the weight of an immersed object.
== C ==
calculus
A branch of mathematics that studies change
and has two major sub-fields: differential
calculus (concerning rates of change and slopes
of curves), and integral calculus (concerning
accumulation of quantities and the areas under
and between curves). These two branches are
related to each other by the fundamental theorem
of calculus.
capacitance
capacitive reactance
Carnot cycle
Cartesian coordinates
cathode
The electrode through which a conventional
electric current flows out of a polarized
electrical device; the direction of current
flow is, by convention, opposite to the direction
of electron flow, and so electrons flow into
the cathode. In a galvanic cell, the cathode
is the positive terminal or pole which accepts
electrons flowing from the external part of
an electrical circuit. However, in an electrolytic
cell, the cathode is the wire or plate having
excess negative charge, so named because positively
charged cations tend to move towards it. Contrast
anode.
cathode ray
cation
A positively charged ion. Contrast anion.
celestial mechanics
Celsius scale
A scale and unit of measurement of temperature,
also known as Centigrade.
center of curvature
center of gravity
The point in a body around which the resultant
torque due to gravity forces vanish. Near
the surface of the earth, where the gravity
acts downward as a parallel force field, the
center of gravity and the center of mass are
the same.
center of mass
A distribution of mass in space is the unique
point where the weighted relative position
of the distributed mass sums to zero.
center of pressure
centigrade
A scale and unit of measurement of temperature,
also known as Celsius.
central force motion
central limit theorem
centrifugal force
The apparent outward force that draws a rotating
body away from the centre of rotation. It
is caused by the inertia of the body as the
body's path is continually redirected.
centripetal force
A force which keeps a body moving with a uniform
speed along a circular path and is directed
along the radius towards the centre.
cGh physics
chain reaction
A sequence of reactions in which a reactive
product or byproduct causes additional similar
reactions to take place.
change of base rule
charge carrier
chemical physics
A branch of chemistry and physics that studies
chemical processes from the point of view
of physics by investigating physicochemical
phenomena using techniques from atomic and
molecular physics and condensed matter physics.
chromatic aberration
circular motion
classical mechanics
Also called Newtonian mechanics.
A sub-field of mechanics concerned with the
set of physical laws describing the motion
of bodies under the collective actions of
a system of forces.
coefficient of friction
coherence
cohesion
The tendency of similar particles or surfaces
to cling to one another. Contrast adhesion.
cold fusion
complex harmonic motion
composite particle
Compton scattering
concave lens
condensation point
condensed matter physics
A branch of physics that studies the physical
properties of condensed phases of matter.
conservation of momentum
conservation law
constructive interference
continuous spectrum
continuum mechanics
convection
The transfer of heat by the actual transfer
of matter.
convex lens
coulomb (C)
The SI derived unit of electric charge, defined
as the charge transported by a constant current
of one ampere in one second.
Coulomb's law
converging lens
cosmic background radiation
covalent bond
creep
crest
The point on a wave with the maximum value
or upward displacement within a cycle.
crest factor
critical angle
critical mass
The smallest amount of fissile material needed
for a sustained nuclear chain reaction.
Curie temperature
current density
current length
curvilinear motion
cyclotron
A type of particle accelerator in which charged
particles accelerate outwards from the center
along a spiral path.
== D ==
Dalton's law
damped vibration
damping
Darcy–Weisbach equation
dark energy
dark matter
DC motor
A mechanically commutated electric motor powered
by direct current.
decibel
definite integral
deflection
The degree to which a structural element is
displaced under a load. It may refer to an
angle or a distance.
deformation
1. (mechanics)
2. (engineering)
density
Also called mass density.
A physical property of a substance defined
as its mass per unit volume.
derivative
desert
destructive interference
diamagnetism
dielectric
diffraction
direct current (DC)
dispersion
displacement (fluid)
Occurs when an object is immersed in a fluid,
pushing it out of the way and taking its place.
The volume of the fluid displaced can then
be measured, and from this the volume of the
immersed object can be deduced (the volume
of the immersed object will be exactly equal
to the volume of the displaced fluid).
displacement (vector)
The shortest distance from the initial to
the final position of a point. Thus, it is
the length of an imaginary straight path,
typically distinct from the path actually
travelled by.
distance
A numerical description of how far apart objects
are.
drift velocity
Doppler effect
The change in frequency of a wave (or other
periodic event) for an observer moving relative
to its source.The received frequency is higher
(compared to the emitted frequency) during
the approach, it is identical at the instant
of passing by, and it is lower during the
recession.
drag
Forces which act on a solid object in the
direction of the relative fluid flow velocity.
Unlike other resistive forces, such as dry
friction, which is nearly independent of velocity,
drag forces depend on velocity.
ductility
A solid material's ability to deform under
tensile stress; this is often characterized
by the material's ability to be stretched
into a wire.
dynamics
The branch of classical mechanics that studies
forces and torques and their effects on motion,
as opposed to kinematics, which studies motion
without reference to these forces.
dyne
== E ==
econophysics
elastic collision
elastic energy
elastic instability
elastic modulus
elasticity
The tendency of a material to return to its
original shape after it is deformed.
electric charge
A physical property of matter that causes
it to experience a force when near other electrically
charged matter. There are two types of electric
charge: positive and negative.
electric circuit
An electrical network consisting of a closed
loop, giving a return path for the current.
electric current
A flow of electric charge through a conductive
medium.
electric displacement field
electric field
The region of space surrounding electrically
charged particles and time-varying magnetic
fields. The electric field depicts the force
exerted on other electrically charged objects
by the electrically charged particle the field
is surrounding.
electric field gradient
electric field intensity
electric generator
electric motor
electric potential
electric power
The rate at which electric energy is transferred
by an electric circuit.
electrical conductor
Any material which contains movable electric
charges and therefore can conduct an electric
current under the influence of an electric
field.
electrical insulator
Any material whose internal electric charges
do not flow freely and which therefore does
not conduct an electric current under the
influence of an electric field.
electrical potential energy
electrical and electronics engineering
electrical network
An interconnection of electrical elements
such as resistors, inductors, capacitors,
voltage sources, current sources and switches.
electrical resistance
The opposition to the passage of an electric
current through an electrical element.
electricity
The set of physical phenomena associated with
the presence and flow of electric charge.
electro-optic effect
electrochemical cell
electrodynamics
electrolytic cell
electromagnet
A type of magnet in which the magnetic field
is produced by the flow of electric current.
electromagnetic field
Also abbreviated EM field or EMF.
A physical field produced by moving electrically
charged objects.
electromagnetic induction
electromagnetic radiation
Also abbreviated EM radiation or EMR.
A form of energy emitted and absorbed by charged
particles, which exhibits wave-like behavior
as it travels through space.
electromagnetic spectrum
electromagnetic wave equation
electromagnetism
electromechanics
electromotive force (
E
{\displaystyle {\mathcal {E}}}
)
Also abbreviated emf.
The electrical intensity or "pressure" developed
by a source of electrical energy such as a
battery or generator and measured in volts.
Any device that converts other forms of energy
into electrical energy provides electromotive
force as its output.
electron
A subatomic particle with a negative elementary
electric charge.
electron capture
electron cloud
electron pair
electron paramagnetic resonance
Also called electron spin resonance (ESR)
and electron magnetic resonance (EMR).
A method for studying materials with unpaired
electrons which makes use of the Zeeman effect.
It shares some basic principles with nuclear
magnetic resonance (NMR).
electronvolt (eV)
A unit of energy equal to approximately 1.6×10−19
joule. By definition, it is the amount of
energy gained by the charge of a single electron
moved across an electric potential difference
of one volt.
electronegativity
A chemical property that describes the tendency
of an atom or a functional group to attract
electrons (or electron density) towards itself.
electronics
A field that deals with electrical circuits
that involve active electrical components
such as vacuum tubes, transistors, diodes
and integrated circuits, and associated passive
interconnection technologies.
electrostatics
electrostriction
elementary charge
elementary particle
emission spectrum
emissivity
energy
The ability to do work.
energy level
endothermic
An adjective used to refer to a process or
reaction in which a system absorbs energy
from its surroundings, usually in the form
of heat but also in the form of light, electricity,
or sound. Contrast exothermic.
engineering physics
enthalpy
entropy
A quantity which describes the randomness
of a substance or system.
equilibrant force
equipartition
escape velocity
The velocity at which the kinetic energy plus
the gravitational potential energy of an object
is zero. It is the speed needed to "escape"
from a gravitational field without further
propulsion.
excited state
exothermic
An adjective used to refer to a process or
reaction that releases energy from a system,
usually in the form of heat but also in the
form of light, electricity, or sound. Contrast
endothermic.
experimental physics
== F ==
farad
falling bodies
Objects that are moving towards a body with
greater gravitational influence, such as a
planet.
faraday
Faraday constant
Fermat's principle
Fermi surface
fermion
A type of particle that behaves according
to Fermi–Dirac statistics, obeys the Pauli
exclusion principle, and possesses half-integer
spin. Fermions include all quarks and leptons,
as well as all composite particles made of
an odd number of these (such as all baryons
and many atoms and nuclei). Fermions constitute
one of two main classes of particles, the
other being bosons.
ferrimagnetism
ferromagnetism
field line
FIRST
An organization founded by inventor Dean Kamen
in 1989 in order to develop ways to inspire
students in engineering and technology fields.
first law of thermodynamics
fission
Either a nuclear reaction or a radioactive
decay process in which the nucleus of an atom
splits into smaller parts (lighter nuclei),
often producing free neutrons and photons
(in the form of gamma rays), and releasing
a, relatively, very large amount of energy.
flavour
fluid
fluid mechanics
fluid physics
fluid statics
fluorescence
flux
flux density
focal length
focus
force (F)
Any interaction that, when unopposed, will
change the motion of a physical body. A force
has both magnitude and direction, making it
a vector quantity. The SI unit used to measure
force is the newton.
force carrier
frame of reference
Fraunhofer lines
free body diagram
frequency
frequency modulation
free fall
Any motion of a body where its own weight
is the only force acting upon it.
freezing point
The temperature at which a substance changes
state from liquid to solid.
friction
function
fundamental forces
Also called fundamental interactions.
fundamental frequency
fundamental theorem of calculus
fusion
A nuclear reaction in which two or more atomic
nuclei join together, or "fuse", to form a
single heavier nucleus.
== G ==
gamma ray
A form of electromagnetic radiation of high
frequency and therefore high energy.
gas
general relativity
geophysics
gluon
Graham's law of diffusion
gravitation
Also called gravity.
A natural phenomenon by which physical bodies
attract each other with a force proportional
to their masses.
gravitational constant (G)
Also called the universal gravitational constant
and Newton's constant.
A physical constant involved in the calculation
of gravitational force between two bodies.
gravitational energy
The potential energy associated with the gravitational
field.
gravitational field
A model used to explain the influence that
a massive body extends into the space around
itself, producing a force on another massive
body. Thus, a gravitational field is used
to explain gravitational phenomena. It is
measured in newtons per kilogram (N/kg).
gravitational potential
The gravitational potential at a location
is equal to the work (energy transferred)
per unit mass that is done by the force of
gravity to move an object to a fixed reference
location.
gravitational wave
A ripple in the curvature of spacetime that
propagates as a wave and is generated in certain
gravitational interactions, travelling outward
from their source.
graviton
gravity
See gravitation.
ground
ground reaction force
ground state
group velocity
== H ==
hadron
half-life
The 
time required for a quantity to fall to half
its value as measured at the beginning of
the time period. In physics, half-life typically
refers to a property of radioactive decay,
but may be refer to any quantity which follows
an exponential decay.
Hamilton's principle
Hamiltonian mechanics
harmonic mean
heat
A form of energy transferred from one body
to another by thermal interaction.
heat transfer
Helmholtz free energy
Henderson–Hasselbalch equation
Henry's law
hertz
The SI unit of frequency defined as the number
of cycles per second of a periodic phenomenon.
Higgs boson
homeokinetics
The physics of complex, self-organizing systems.
horsepower
Huygens–Fresnel principle
hydrostatics
== I ==
ice point
A physical process that results in the phase
transition of a substance from a liquid to
a solid.
impedance
The measure of the opposition that a circuit
presents to a current when a voltage is applied.
indefinite integral
inductance
infrasound
inertia
The resistance of any physical object to a
change in its state of motion or rest, or
the tendency of an object to resist any change
in its motion.
inductive reactance
integral
integral transform
International System of Units
The International System of Units (abbreviated
SI) is the modern form of the metric system.
It comprises a system of units of measurement
devised around seven base units and the convenience
of the number ten.
invariant mass
ion
An atom or molecule in which the total number
of electrons is not equal to the total number
of protons, giving the atom a net positive
or negative electric charge.
ionic bond
A type of chemical bond formed through an
electrostatic attraction between two oppositely
charged ions.
ionization
The process of converting an atom or molecule
into an ion by adding or removing charged
particles such as electrons or other ions.
ionization chamber
ionizing radiation
isotope
A variant of a particular chemical element.
While all isotopes of a given element share
the same number of protons, each isotope differs
from the others in its number of neutrons.
== J ==
Josephson effect
joule
A derived unit of energy, work, or amount
of heat in the International System of Units.
== K ==
Kelvin
A scale and unit of measurement of temperature.
The Kelvin scale is an absolute thermodynamic
temperature scale which uses absolute zero
as its null point.
kinematics
The branch of classical mechanics that describes
the motion of points, bodies (objects) and
systems of bodies (groups of objects) without
consideration of the causes of motion. The
study of kinematics is often referred to as
the "geometry of motion".
kinetic energy
The energy that a physical body possesses
due to its motion, defined as the work needed
to accelerate a body of a given mass from
rest to its stated velocity. The body continues
to maintain this kinetic energy unless its
velocity changes. Contrast potential energy.
Kirchhoff's circuit laws
Two approximate equalities that deal with
the current and voltage in electrical circuits.also
called Kirchhoff's rules or simply Kirchhoff's
laws (see also Kirchhoff's laws for other
meanings of that term).
Kirchhoff's equations
In fluid dynamics, the Kirchhoff equations
describe the motion of a rigid body in an
ideal fluid.
== L ==
Lagrangian mechanics
laminar flow
Also called streamline flow.
Occurs when a fluid flows in parallel layers
with no disruption between the layers.
Laplace transform
Laplace–Runge–Lenz vector
Also abbreviated LRL vector.
A vector used chiefly to describe the shape
and orientation of the orbit of one astronomical
body around another, such as a planet revolving
around a star. For two bodies interacting
by Newtonian gravity, the LRL vector is a
constant of motion, meaning that it is the
same no matter where it is calculated on the
orbit; equivalently, the LRL vector is said
to be conserved.
laser
law of universal gravitation
LC circuit
Lenz's law
lepton
An elementary particle which does not undergo
strong interactions but is subject to the
Pauli exclusion principle. Two main classes
of leptons exist: charged leptons (also known
as the electron-like leptons) and neutral
leptons (better known as neutrinos).
lever
A type of machine consisting of a beam or
rigid rod pivoted at a fixed hinge or fulcrum;
one of six classical simple machines.
light
A form of electromagnetic radiation that occupies
a certain range of wavelengths within the
electromagnetic spectrum. In physics, the
term sometimes refers collectively to electromagnetic
radiation of any wavelength, in which case
light includes gamma rays, X-rays, microwaves,
and radio waves, but in common usage "light"
more often refers specifically to visible
light.
linear actuator
A form of motor that generates a linear movement
directly.
linear algebra
The branch of mathematics concerning vector
spaces, often finite or countably infinite
dimensional, as well as linear mappings between
such spaces.
line of force
linear elasticity
The mathematical study of how solid objects
deform and become internally stressed due
to prescribed loading conditions. Linear elasticity
is a simplification of the more general nonlinear
theory of elasticity and is a branch of continuum
mechanics.
Liouville's theorem
Phase space volume is conserved.
liquid
One of four classical states of matter having
a definite volume but no fixed shape.
liquid crystal (LC)
A matter in a state that has properties between
those of a conventional liquid and those of
a solid crystal. For instance, an LC may flow
like a liquid, but its molecules may be oriented
in a crystal-like way.
longitudinal wave
== M ==
M-theory
An extension of string theory that attempts
to unify seemingly contradictory mathematical
formulations and which identifies 11 dimensions.
Mach number
A dimensionless quantity representing the
ratio of the speed of an object moving through
a fluid to the local speed of sound.
machine
Any powered tool consisting of one or more
parts that is constructed to achieve a particular
goal. Machines are usually powered by mechanical,
chemical, thermal or electrical means, and
are frequently motorised.
machine element
An elementary component of a machine. There
are three basic types: structural components,
mechanisms and control components.
Maclaurin series
A representation of a function as an infinite
sum of terms that are calculated from the
values of the function's derivatives at a
single point.
magnetic field
A mathematical description of the magnetic
influence of electric currents and magnetic
materials. The magnetic field at any given
point is specified by both a direction and
a magnitude (or strength); as such it is a
vector field.
magnetism
A property of materials that respond to an
applied magnetic field.
magnetostatics
mass
mass balance
Also called material balance.
An application of the law of conservation
of mass to the analysis of physical systems.
mass density
See density.
mass flux
The rate of mass flow per unit area. The common
symbols are j, J, φ, or Φ, sometimes with
subscript m to indicate mass is the flowing
quantity. Its SI units are kg s−1 m−2.
mass moment of inertia
A property of a distribution of mass in space
that measures its resistance to rotational
acceleration about an axis.
mass number
Also called atomic mass number or nucleon
number.
The total number of protons and neutrons (together
known as nucleons) in an atomic nucleus.
mass spectrometry
material properties
materials science
An interdisciplinary field incorporating elements
of physics, chemistry, and engineering that
is concerned with the design and discovery
of new materials, particularly solids.
mathematical physics
The application of mathematics to problems
in physics and the development of mathematical
methods suitable for such applications and
for the formulation of physical theories.
mathematics
The abstract study of topics encompassing
quantity, structure, space, change, and other
properties.
matrix
A rectangular array of numbers, symbols, or
expressions arranged in rows and columns.
The individual items in a matrix are called
its elements or entries.
matter
Any substance (often a particle) that has
rest mass and (usually) also volume.
Maxwell's equations
A set of partial differential equations that,
together with the Lorentz force law, form
the foundation of classical electrodynamics,
classical optics, and electric circuits. Maxwell's
equations describe how electric and magnetic
fields are generated and altered by each other
and by charges and currents.
measure of central tendency
A term which relates to the way in which quantitative
data tend to cluster around some value. A
measure of central tendency is any of a number
of ways of specifying this "central value".
mechanical energy
mechanical filter
mechanical equilibrium
mechanical wave
mechanics
The branch of science concerned with the behaviour
of physical bodies when subjected to forces
or displacements and the subsequent effects
of the bodies on their environment.
melting
Also called fusion.
A physical process that results in the phase
transition of a substance from a solid to
a liquid.
meson
A type of hadronic subatomic particle composed
of one quark and one antiquark bound together
by the strong interaction. All mesons are
unstable, with the longest-lived lasting for
only a few hundredths of a microsecond.
modulus of elasticity
The mathematical description of an object's
or substance's tendency to be deformed elastically
(i.e., non-permanently) when a force is applied
to it. The elastic modulus of an object is
defined as the slope of its stress–strain
curve in the elastic deformation region. As
such, a stiffer material will have a higher
elastic modulus.
molar concentration
molar mass
A physical property of matter defined as the
mass of a given substance divided by the amount
of substance and expressed in grams per mole.
molecule
An electrically neutral group of two or more
atoms held together by covalent chemical bonds.
Molecules are distinguished from ions by their
lack of electrical charge.
molecular physics
A branch of physics that studies the physical
properties of molecules and the chemical bonds
between atoms as well as their molecular dynamics.
It is closely related to atomic physics and
overlaps greatly with theoretical chemistry,
physical chemistry and chemical physics.
moment
moment of inertia
A property of a distribution of mass in space
that measures its resistance to rotational
acceleration about an axis.
monochromatic light
motion
Any change in the position of an object over
time. Motion can be mathematically described
in terms of displacement, distance, velocity,
speed, acceleration, and momentum, and is
observed by attaching a frame of reference
to an observer and measuring the change in
an object's position relative to that frame.
An object's motion cannot change unless it
is acted upon by a force.
muon
An elementary particle, technically classified
as a lepton, that is similar to the electron,
with unitary negative electric charge (−1)
and a spin of 1⁄2. Muons are not believed
to have any sub-structure.
== N ==
nanoengineering
The practice of engineering on the nanoscale.
Nanoengineering is largely a synonym for nanotechnology,
but emphasizes the applied rather than the
pure science aspects of the field.
nanotechnology
Also abbreviated as nanotech.
The manipulation of matter on an atomic and
molecular scale. A more generalized description
of nanotechnology is "the manipulation of
matter with at least one dimension sized from
1 to 100 nanometers".
Navier–Stokes equations
neurophysics
neutrino
A type of electrically neutral subatomic particle
denoted by the Greek letter ν (nu). All evidence
suggests that neutrinos have mass but that
their mass is tiny even by the standards of
subatomic particles. Their mass has never
been measured accurately.
neutron
neutron cross-section
newton (N)
Newton's laws of motion
A set of three physical laws which describe
the relationship between the forces acting
on a body and its motion due to those forces.
Together they form the basis for classical
or Newtonian mechanics.
Newton's law of universal gravitation
Newtonian fluid
Newtonian mechanics
normal force
nth root
nuclear force
nuclear physics
The branch of physics that studies the constituents
and interactions of atomic nuclei.
nuclear reaction
nuclear transmutation
nucleon
Either a proton or a neutron in its role as
a component of an atomic nucleus.
nucleus
nuclide
Also spelled nucleide.
An atomic species characterized by the specific
composition of its nucleus, i.e. by its number
of protons, its number of neutrons, and its
nuclear energy state.
== O ==
Ohm
The SI derived unit of electrical resistance.
Ohm's law
States that the current through a conductor
between two points is directly proportional
to the potential difference across the two
points.
optical tweezers
An optomechanical device used for the capture,
analysis and manipulation of dielectric objects
or particles, which operates via the application
of force by the electric field of light.
optically detected magnetic resonance
An optical technique for the initialisation
and readout of quantum spin in some crystal
defects.
optics
The branch of physics which involves the behaviour
and properties of light, including its interactions
with matter and the construction of instruments
that use or detect it. Optics usually describes
the behaviour of visible, ultraviolet, and
infrared light; however, because light is
one of several forms of electromagnetic radiation,
other forms such as X-rays, microwaves, and
radio waves exhibit similar properties.
== P ==
paraffin
parallel circuit
parity
1. (mathematics)
2. (physics)
particle
particle accelerator
particle displacement
particle physics
A branch of physics that studies the nature
of particles, which are the constituents of
what is usually referred to as matter and
radiation.
Pascal's law
A principle in fluid mechanics which states
that pressure exerted anywhere in a confined
incompressible fluid is transmitted equally
in all directions throughout the fluid such
that the initial pressure variations remain
the same.
Pauli exclusion principle
pendulum
periodic table of the elements
Also simply called the periodic table.
A tabular display of the chemical elements
organised on the basis of their atomic numbers,
electron configurations, and recurring chemical
properties. Elements are presented in order
of increasing atomic number (number of protons).
phase (matter)
phase (waves)
phase equilibrium
phenomenology
phosphorescence
photoelectric effect
photon
An elementary particle, the quantum of light
and all other forms of electromagnetic radiation,
and the force carrier for the electromagnetic
force.
photonics
physical chemistry
The study of macroscopic, atomic, subatomic,
and particulate phenomena in chemical systems
in terms of laws and concepts of physics.
physical constant
physical quantity
physics
The natural science that involves the study
of matter and its motion through space and
time, along with related concepts such as
energy and force. More broadly, it is the
general analysis of nature, conducted in order
to understand how the universe behaves.
piezoelectricity
pion
Planck constant (h)
Also called Planck's constant.
A physical constant that is the quantum of
action in quantum mechanics.
Planck units
Planck's law
plasma
plasma physics
plasticity
pneumatics
The study and control of mechanical force
and movement generated by the application
of compressed gas.
positron
potential energy
power
pressure
The ratio of force to the area over which
that force is distributed.
probability
A measure of the expectation that an event
will occur or that a statement is true. Probabilities
are given a value between 0 (will not occur)
and 1 (will occur). The higher the probability
of an event, the more certain one can be that
the event will occur.
probability distribution
probability theory
proton
psi particle
pulley
A wheel on an axle that is designed to support
movement of a cable or belt along its circumference;
one of six classical simple machines. Pulleys
are used in a variety of ways to lift loads,
apply forces, and transmit power.
pulse
pulse wave
== Q ==
quantization
quantum
quantum chromodynamics
quantum electrodynamics
The relativistic quantum field theory of electrodynamics.
In essence, it describes how light and matter
interact and is the first theory where full
agreement between quantum mechanics and special
relativity is achieved. QED mathematically
describes all phenomena involving electrically
charged particles interacting by means of
exchange of photons and represents the quantum
counterpart of classical electromagnetism,
giving a complete account of matter and light
interaction.
quantum field theory
A theoretical framework for constructing quantum
mechanical models of subatomic particles in
particle physics and quasiparticles in condensed
matter physics.
quantum gravity
quantum mechanics
A branch of physics dealing with physical
phenomena at microscopic scales, where the
action is on the order of the Planck constant.
Quantum mechanics departs from classical mechanics
primarily at the quantum realm of atomic and
subatomic length scales. Quantum mechanics
provides a mathematical description of much
of the dual particle-like and wave-like behavior
and interactions of energy and matter.
quantum number
quantum physics
quantum state
quark
An elementary particle and a fundamental constituent
of matter. Quarks combine to form composite
particles called hadrons, the most stable
of which are protons and neutrons, the components
of atomic nuclei.
quasiparticle
== R ==
radiant energy
radiation
radioactive decay
radionuclide
Also called a radioactive nuclide, radioisotope,
or radioactive isotope.
Any nuclide possessing excess nuclear energy
to the point that it is unstable. Such excess
energy is emitted through any of several processes
of radioactive decay, resulting in a stable
nuclide or sometimes another unstable radionuclide
which can then undergo further decay. Certain
radionuclides can occur naturally; many others
can be produced artificially in nuclear reactors,
cyclotrons, particle accelerators, or radionuclide
generators.
radius of curvature
redshift
A phenomenon which occurs when light seen
coming from an object that is moving away
is proportionally increased in wavelength
or "shifted" to the red end of the visible
light spectrum.
refraction
The change in direction of a wave as it passes
from one transmission medium to another or
as a result of a gradual change in the medium.
Though most commonly used in the context of
refraction of light, other waves such as sound
waves and fluid waves also experience refraction.
refractive index
relative atomic mass
relativistic mechanics
rigid body
An idealization of a solid body in which deformation
is neglected. In other words, the distance
between any two given points of a rigid body
remains constant in time regardless of the
external forces exerted on it. Even though
such an object cannot physically exist due
to relativity, objects can normally be assumed
to be perfectly rigid if they are not moving
near the speed of light.
rotational energy
Also called angular kinetic energy.
The kinetic energy due to the rotation of
an object and forms part of its total kinetic
energy.
rotational speed
Also called speed of revolution.
The number of complete rotations or revolutions
a rotating body makes per unit time.
Rydberg formula
A formula used in atomic physics to describe
the wavelengths of spectral lines of many
chemical elements.
== S ==
scalar
Any simple physical quantity that can be described
by a single number (as opposed to vectors,
tensors, etc., which are described by several
numbers such as magnitude and direction) and
is unchanged by coordinate system rotations
or translations (in Newtonian mechanics) or
by Lorentz transformations or central-time
translations (in relativity).
scattering
The general physical process by which some
forms of radiation, such as light, sound,
or moving particles, are forced to deviate
from a straight trajectory by one or more
localised non-uniformities in the medium through
which they pass.
science
A systematic enterprise that builds and organises
knowledge in the form of testable explanations
and predictions about the universe.
screw
A mechanism that converts rotational motion
to linear motion, and a torque (rotational
force) to a linear force; one of six classical
simple machines.
second law of thermodynamics
Seebeck effect
series circuit
shadow matter
shear modulus
Also called modulus of rigidity.
shear strength
shear stress
shortwave radiation
Schrödinger equation
A mathematical equation which describes the
time evolution of wave functions in quantum
mechanics.
simple harmonic motion
simple machine
A mechanical device that changes the direction
or magnitude of a force. In general, a set
of six classical simple machines identified
by Renaissance scientists drawing from Greek
texts on technology are collectively defined
as the simplest mechanisms that can provide
mechanical advantage (also called leverage).
siphon
A tube in an inverted U shape that causes
a liquid to flow uphill without pumps, powered
by the fall of the liquid as it flows down
the tube under the pull of gravity. The term
may also more generally refer to a wide variety
of devices involving the flow of liquids through
tubes.
Snell's law
solar cell
solid
solid mechanics
solid-state physics
solubility
The tendency of a solid, liquid, or gaseous
chemical substance (called a solute) to dissolve
in another solid, liquid, or gaseous substance
(called a solvent) to form a homogeneous solution
of the solute in the solvent. The solubility
of a solute fundamentally depends on the specific
solvent as well as on temperature and pressure.
sound
A mechanical wave that is an oscillation of
pressure transmitted through a solid, liquid,
or gas and composed of frequencies within
the range of human hearing.
special relativity
specific activity
speed
speed of light (c)
A universal physical constant defined as exactly
299,792,458 metres per second, a figure that
is exact because the length of the metre is
defined from this constant and the international
standard for time. When not otherwise qualified,
the term "speed of light" usually refers to
the speed of light in a vacuum as opposed
to the speed of light through some physical
medium.
speed of sound
spherical aberration
spin quantum number
stable isotope ratio
stable nuclide
Any nuclide that is not radioactive and does
not spontaneously undergo radioactive decay,
as opposed to a radionuclide. When such nuclides
are referred to in relation to specific elements,
they are usually termed stable isotopes.
standard atomic weight
Standard Model
The theory of particle physics which describes
three of the four known fundamental forces
(the electromagnetic force, the weak force,
and the strong force, but not the gravitational
force) and classifies all known elementary
particles.
standing wave
state of matter
statics
The branch of mechanics concerned with the
analysis of loads (force and torque, or "moment")
on physical systems in static equilibrium,
that is, in a state where the relative positions
of subsystems do not vary over time, or where
components and structures are at a constant
velocity.
statistical mechanics
stiffness
The rigidity of an object — the extent to
which it resists deformation in response to
an applied force.
strain
The transformation of a body from a reference
configuration to a current configuration.[1]
A configuration is a set containing the positions
of all particles of the body.
strain hardening
strength of materials
stress
1. An applied force or system of forces that
tends to strain or deform a physical body.
2. A measure of the internal forces acting
within a deformable body.
3. A quantitative measure of the average force
per unit area of a surface within a body on
which internal forces act.
stress–strain curve
string duality
string theory
structural load
subatomic particle
Any particle that is smaller than an atom.
sublimation
The process of transformation directly from
the solid phase to the gas phase without passing
through an intermediate liquid phase. Sublimation
is an endothermic phase transition that occurs
at temperatures and pressures below a substance's
triple point in its phase diagram.
superconductivity
superconductor
A phenomenon of exactly zero electrical resistance
and expulsion of magnetic fields occurring
in certain materials when cooled below a characteristic
critical temperature.
superhard material
superposition principle
supersymmetry (SUSY)
surface tension
== T ==
temperature
A physical property of matter that quantitatively
expresses the common notions of hot and cold.
tensile modulus
tensile strength
tesla (T)
test particle
theoretical physics
theory of everything
theory of relativity
thermal conduction
thermal equilibrium
A state in which there is no net flow of thermal
energy between two physical systems when the
systems are connected by a path permeable
to heat. A system may also be said to be in
thermal equilibrium with itself if the temperature
within the system is spatially and temporally
uniform. Systems in thermodynamic equilibrium
are always in thermal equilibrium, but the
converse is not always true.
thermal radiation
thermionic emission
thermodynamic equilibrium
thermodynamic free energy
thermodynamics
thermometer
An instrument used to measure temperature.
third law of thermodynamics
threshold frequency
torque
Also called moment or moment of force.
The tendency of a force to rotate an object
about an axis, fulcrum, or pivot. Just as
a force is a push or a pull, a torque can
be thought of as a twist to an object.
total internal reflection
toughness
The ability of a material to absorb energy
and plastically deform without fracturing.
Material toughness is defined as the amount
of energy per unit volume that a material
can absorb before rupturing. It is also defined
as the resistance to fracture of a material
when stressed.
trajectory
The path that a moving object follows through
space as a function of time.
transducer
transmission medium
transverse wave
trigonometry
A branch of mathematics that studies triangles
and the relationships between their sides
and the angles between these sides.
trimean
triple point
The temperature and pressure at which the
three phases (gas, liquid, and solid) of a
given substance coexist in thermodynamic equilibrium.
truncated mean
== U ==
uncertainty principle
Any of a variety of mathematical inequalities
asserting a fundamental limit to the precision
with which certain pairs of physical properties
of a particle, such as position x and momentum
p, can be known simultaneously.
uniform motion
uniform circular motion
unit vector
utility frequency
The frequency of the oscillations of alternating
current (AC) in an electric power grid transmitted
from a power plant to the end-user.
== V ==
vacuum
An area of space which contains no matter.
valence electron
An electron that is associated with an atom
and can participate in the formation of a
chemical bond.
valence shell
The outermost electron shell of an atom.
valley of stability
Van de Graaff generator
variable capacitor
variable resistor
vector
Any quantity that has both magnitude and direction.
vector space
A mathematical structure formed by a collection
of elements called vectors, which may be added
together and multiplied ("scaled") by numbers
called scalars.
velocity
virtual image
virtual particle
viscoelasticity
viscosity
visible light
A form of electromagnetic radiation generally
defined as the range of wavelengths visible
to the average human eye.
volt (V)
The SI derived unit for electric potential,
electric potential difference, and electromotive
force, defined as the difference in electric
potential between two points of a conducting
wire when an electric current of one ampere
dissipates one watt of power between those
two points.
Volta potential
voltage
voltmeter
An instrument used for measuring the difference
in electrical potential between two points
in an electric circuit. Analog voltmeters
move a pointer across a scale in proportion
to the voltage of the circuit.
volt per meter
volume
== W ==
W and Z bosons
watt (W)
A derived unit of power in the International
System of Units (SI) defined as one joule
per second. The watt measures the rate of
energy conversion or transfer.
wave
A disturbance or oscillation that travels
through spacetime accompanied by a transfer
of energy.
wave equation
wave function
wave function collapse
wave–particle duality
wavelength
A measure of the distance traversed by a single
spatial period of a sinusoidal wave, i.e.
the distance over which the wave's shape repeats.
weak interaction
Also called the weak force or weak nuclear
force.
One of the four fundamental forces of nature,
along with the strong nuclear force, electromagnetism,
and gravitation. It is responsible for the
radioactive decay of subatomic particles and
initiates the process known as hydrogen fusion
in stars.
weber (Wb)
wedge
A triangular round tool in the form a compound
and portable inclined plane; one of six classical
simple machines.
weight
wheel and axle
A wheel attached to an axle so that these
two parts rotate together in which a force
is transferred from one to the other; one
of six classical simple machines.
white body
A hypothetical idealized physical body that
reflects all incident electromagnetic radiation
completely and uniformly in all directions;
the opposite of a black body.
wind
The flow of gases on a large scale.
wind shear
Also called wind gradient.
A difference in wind speed and direction over
a relatively short distance in the atmosphere.
Wind shear can be broken down into vertical
and horizontal components, with horizontal
wind shear seen across fronts and near the
coast, and vertical shear typically near the
surface, though also at higher levels in the
atmosphere.
work
work function
== X ==
X-ray
A high-energy photon (between 100 eV and 100
keV) with a wavelength shorter than that of
ultraviolet radiation and longer than that
of gamma radiation.
== Y ==
Young’s modulus
A measure of the stiffness of a solid material
which defines the relationship between mechanical
stress and strain.
== Z ==
Zeeman effect
The effect of splitting a spectral line into
several components in the presence of a static
magnetic field by the lifting of degeneracy
in electronic states.
== See also ==
Outline of physics
Index of physics articles
Glossary of areas of mathematics
Glossary of astronomy
Glossary of biology
Glossary of calculus
Glossary of chemistry terms
Glossary of engineering
Glossary of probability and statistics
