# Physics glossary A-D

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Question Answer Absolute zero
The lowest theoretical temperature a material can have, where the molecules that make up the material have no kinetic energy. Absolute zero is reached at 0 K or –273º C.
Acceleration
A vector quantity defined as the rate of change of the velocity vector with time.
Activity
In radioactive substances, the number of nuclei that decay per second. Activity, A, will be larger in large samples of radioactive material, since there will be more nuclei.
Alpha decay
A form of radioactive decay where a heavy element emits an alpha particle and some energy, thus transforming into a lighter, more stable, element.
Alpha particle
A particle, which consists of two protons and two neutrons. It is identical to the nucleus of a helium atom and is ejected by heavy particles undergoing alpha decay.
Angle of incidence
When a light ray strikes a surface, the angle of incidence is the angle between the incident ray and the normal.
Angle of reflection
The angle between a reflected ray and the normal.
Angle of refraction
The angle between a refracted ray and the line normal to the surface.
Angular acceleration
A vector quantity, equal to the rate of change of the angular velocity vector with time. It is typically given in units of rad/s2.
Angular displacement
The net change, in a point’s angular position,. It is a scalar quantity.
Angular frequency
A frequency, f, defined as the number of revolutions a rigid body makes in a given time interval. It is a scalar quantity commonly denoted in units of Hertz (Hz) or s–1.
Angular momentum
moment pedu
Angular period
The time, T, required for a rigid body to complete one revolution.
Angular position
The position, of an object according to a co-ordinate system measured in s of the angle of the object from a certain origin axis. Conventionally, this origin axis is the positive x-axis.
Angular velocity
predkosc katowa
Antinode
The points midway between nodes on a standing wave, where the oscillations are largest.
Atom
The building blocks of all matter, atoms are made up of a nucleus consisting of protons and neutrons, and a number of electrons that orbit the nucleus. An electrically neutral atom has as many protons as it has electrons.
Atomic number
A number, Z, associated with the number of protons in the nucleus of an atom. Every element can be defined in s of its atomic number, since every atom of a given element has the same number of protons.
Axis of rotation
The line that every particle in the rotating rigid body circles about.
Basis vector
A vector of magnitude 1 along one of the coordinate axes. Generally, we take the basis vectors to be and, the vectors of length 1 along the x- and y-axes, respectively.
Beats
uderzenia
Beta decay
A form of radioactive decay where a heavy element ejects a beta particle and a neutrino, becoming a lighter element in the process.
Beta particle
A particle, identical to an electron. Beta particles are ejected from an atom in the process of beta decay.
Bohr atomic model
model Bohra
Boiling point
The temperature at which a material will change phase from liquid to gas or gas to liquid.
Boyle’s Law
For a gas held at a constant temperature, pressure and volume are inversely proportional.
Calorie
The amount of heat needed to raise the temperature of one gram of water by one degree Celsius. 1 cal = 4.19 J.
Celsius
A scale for measuring temperature, defined such that water freezes at 0ºC and boils at 100ºC. 0ºC = 273 K.
Center of curvature
With spherical mirrors, the center of the sphere of which the mirror is a part. All of the normals pass through it.
Center of mass
środek masy
Centripetal acceleration
The acceleration of a body experiencing uniform circular motion. This acceleration is always directed toward the center of the circle.
Centripetal force
The force necessary to maintain a body in uniform circular motion. This force is always directed radially toward the center of the circle.
Chain reaction
The particles and energy released by the fission or fusion of one atom may trigger the fission or fusion of further atoms. In a chain reaction, fission or fusion is rapidly transferred to a large number of atoms, releasing tremendous amounts of energy.
Charles’s Law
For a gas held at constant pressure, temperature and volume are directly proportional.
Coefficient of kinetic friction
The coefficient of kinetic friction, for two materials is the constant of proportionality between the normal force and the force of kinetic friction. It is always a number between zero and one.
Coefficient of linear expansion
A coefficient that tells how much a material will expand or contract lengthwise when it is heated or cooled.
Coefficient of static friction
The coefficient of static friction, for two materials is the constant of proportionality between the normal force and the maximum force of static friction. It is always a number between zero and one.
Coefficient of volume expansion
A coefficient that tells how much the volume of a solid will change when it is heated or cooled.
Coherent light
Light such that all of the associated waves have the same wavelength and are in phase.
Collision
zderzenie
Completely inelastic collision
A collision in which the colliding particles stick together.
Component
Compression
kompresja, sprezenie
Concave lens
Also called a diverging lens, a lens that is thinner in the middle than at the edges. Concave lenses refract light away from a focal point.
Concave mirror
A mirror that is curved such that its center is farther from the viewer than the edges, such as the front of a spoon. Concave mirrors reflect light through a focal point.
Conduction
Heat transfer by molecular collisions.
Conservation of Angular Momentum
If the net torque acting on a rigid body is zero, then the angular momentum of the body is constant or conserved.
Conservation of momentum
The principle stating that for any isolated system, linear momentum is constant with time.
Constant of proportionality
A constant in the numerator of a formula.
Constructive interference
The amplification of one wave by another, identical wave of the same sign. Two constructively interfering waves are said to be “in phase.”
Convection
Heat transfer via the mass movement of molecules.
Convex lens
Also called a converging lens, a lens that is thicker in the middle than at the edges. Convex lenses refract light through a focal point.
Convex mirror
A mirror that is curved such that its center is closer to the viewer than the edges, such as a doorknob. Convex mirrors reflect light away from a focal point.
Cosine
The cosine of an angle in a right triangle is equal to the length of the side adjacent to the angle divided by the length of the hypotenuse.
Crest
The points of maximum displacement along a wave. In traveling waves, the crests move in the direction of propagation of the wave. The crests of standing waves, also called anti-nodes, remain in one place.
Critical angle
For two given media, the smallest angle of incidence at which total internal reflection occurs.
Cross product
iloczyn wektorowy
Cycle
cykl
De Broglie wavelength
A wavelength, given by = h/mv, which is associated with matter. Louis de Broglie proposed the idea that matter could be treated as waves in 1923 and applied this theory successfully to small particles like electrons.
Decay constant
A constant, not to be confused with wavelength, that defines the speed at which a radioactive element undergoes decay. The greater is, the faster the element decays.
Decibel
A logorithmic unit for measuring the volume of sound, which is the square of the amplitude of sound waves.
Deposition
The process by which a gas turns directly into a solid because it cannot exist as a liquid at certain pressures.
Destructive interference
The cancellation of one wave by another wave that is exactly out of phase with the first. Despite the dramatic name of this phenomenon, nothing is “destroyed” by this interference—the two waves emerge intact once they have passed each other.
Diffraction
The bending of light at the corners of objects or as it passes through narrow slits or apertures.
Diffraction grating
A sheet, film, or screen with a pattern of equally spaced slits. Typically the width of the slits and space between them is chosen to generate a particular diffraction pattern.
Direction
kierunek
Directly proportional
wprost proporcjonalnie
Dispersion
The separation of different color light via refraction.
Displacement
przesunięcie (wektor)
Distance
odleglosc (skalar)
Doppler shift
przesuniecie dopplerowskie
Dot product
A form of vector multiplication, where two vectors are multiplied to produce a scalar. The dot product of two vectors, A and B, is expressed by the equation A · B = AB cos.
Dynamics
The application of kinematics to understand why objects move the way they do. More precisely, dynamics is the study of how forces cause motion.