GCSE Physics glossary

Short definitions for GCSE Physics, with SI units where they apply. Check your own exam board’s specification for the exact terms it uses.

A

Absolute zero

Lowest possible temperature, 0 K (about -273 °C), at which particles have as little kinetic energy as possible. See also: Kelvin.

Acceleration

Rate of change of velocity. Unit: metre per second squared (m/s²). See also: Velocity.

Activity

Number of nuclei in a radioactive source that decay each second. Unit: becquerel (Bq). See also: Half-life.

Alpha particle

A helium nucleus (two protons and two neutrons) emitted from an unstable nucleus. It is strongly ionising and has a very short range in air. See also: Beta particle.

Amplitude

Maximum displacement of a point on a wave from its rest position. Unit: metre (m) for many waves. See also: Wavelength.

Atomic number

Number of protons in the nucleus of an atom. It identifies the element. See also: Mass number.

B

Background radiation

Low-level ionising radiation that is always present from natural sources such as rocks and cosmic rays, and from human-made sources. See also: Activity.

Beta particle

A fast electron emitted from the nucleus when a neutron changes into a proton. It is moderately ionising. See also: Alpha particle.

C

Centre of mass

Point where the weight of an object can be considered to act. See also: Weight.

Conduction

Transfer of thermal energy through a material by particles passing on vibrations, and by free electrons in metals. See also: Convection.

Contamination

Unwanted presence of radioactive material on or inside an object, so the object itself is a source of radiation. See also: Irradiation.

Convection

Transfer of thermal energy in a fluid, where warmer, less dense regions rise and cooler, denser regions sink. See also: Conduction.

Current

Rate of flow of electric charge. Unit: ampere (A). See also: Potential difference.

D

Density

Mass per unit volume of a substance, found using mass divided by volume. Unit: kilogram per cubic metre (kg/m³). See also: Specific heat capacity.

Displacement

Straight-line distance from a starting point to a finishing point in a given direction. Unit: metre (m). It is a vector. See also: Distance.

Distance

How far an object has moved along its path. Unit: metre (m). It is a scalar. See also: Displacement.

E

Efficiency

Fraction or percentage of the total energy input that is transferred to a useful form. See also: Power.

Elastic potential energy

Energy stored in a stretched or compressed object such as a spring. Unit: joule (J). See also: Gravitational potential energy.

Electromagnetic wave

A transverse wave that can travel through a vacuum at the same speed, with types arranged by wavelength and frequency in the electromagnetic spectrum. See also: Frequency.

F

Force

A push or pull that acts on an object. Unit: newton (N). It is a vector. See also: Resultant force.

Frequency

Number of complete waves passing a point each second. Unit: hertz (Hz). See also: Period.

Friction

A force between two surfaces in contact that opposes relative motion or the tendency to move. See also: Resultant force.

G

Gravitational field strength

Force acting on each kilogram of mass in a gravitational field. Unit: newton per kilogram (N/kg). See also: Weight.

Gravitational potential energy

Energy stored in an object because of its height in a gravitational field. Unit: joule (J). See also: Kinetic energy.

H

Half-life

Time taken for the number of unstable nuclei in a sample to halve, or for its activity to fall to half. Unit: second (s), or other time units. See also: Activity.

I

Ionisation

Process of an atom gaining or losing electrons to become an ion. See also: Alpha particle.

Irradiation

Exposure of an object to radiation from a source outside it. It does not make the object radioactive. See also: Contamination.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons. See also: Atomic number.

K

Kelvin

SI unit of temperature. A change of 1 K is the same size as a change of 1 °C, and 0 K is absolute zero. See also: Absolute zero.

Kinetic energy

Energy an object has because it is moving. Unit: joule (J). See also: Gravitational potential energy.

L

Longitudinal wave

A wave in which the oscillations are parallel to the direction of energy transfer, such as sound. See also: Transverse wave.

M

Magnetic field

Region around a magnet or current-carrying wire where a magnetic material experiences a force. See also: Solenoid.

Mass

Amount of matter in an object. Unit: kilogram (kg). It does not change with location. See also: Weight.

Mass number

Total number of protons and neutrons in a nucleus. See also: Atomic number.

Moment

Turning effect of a force about a pivot, found using force multiplied by perpendicular distance. Unit: newton metre (Nm). See also: Force.

Momentum

Product of an object's mass and velocity. Unit: kilogram metre per second (kg m/s). See also: Velocity.

N

Neutron

A particle in the nucleus with no electric charge and a relative mass of 1. See also: Proton.

P

Period

Time for one complete wave or oscillation. Unit: second (s). See also: Frequency.

Potential difference

Energy transferred per unit of charge as charge moves between two points in a circuit. Unit: volt (V). See also: Current.

Power

Rate at which energy is transferred, or work is done. Unit: watt (W), where 1 W is 1 J/s. See also: Efficiency.

Proton

A positively charged particle in the nucleus with a relative mass of 1. See also: Neutron.

R

Radioactive decay

Random process in which an unstable nucleus emits radiation to become more stable. See also: Half-life.

Resistance

A measure of how much a component opposes the flow of current. Unit: ohm (Ω). See also: Current.

Resultant force

Single force that has the same effect as all the forces acting on an object combined. See also: Force.

S

Scalar

A quantity that has size only, with no direction, such as mass, speed or energy. See also: Vector.

Solenoid

A coil of wire which, when it carries a current, produces a magnetic field like that of a bar magnet. See also: Magnetic field.

Specific heat capacity

Energy needed to raise the temperature of 1 kg of a substance by 1 °C. Unit: joule per kilogram per degree Celsius (J/kg °C). See also: Density.

Speed

How fast an object is moving, found using distance divided by time. Unit: metre per second (m/s). See also: Velocity.

T

Transverse wave

A wave in which the oscillations are at right angles to the direction of energy transfer, such as light. See also: Longitudinal wave.

V

Vector

A quantity that has both size and direction, such as force, velocity or displacement. See also: Scalar.

Velocity

Speed in a stated direction. Unit: metre per second (m/s). It is a vector. See also: Speed.

W

Wavelength

Distance from a point on one wave to the same point on the next wave. Unit: metre (m). See also: Frequency.

Weight

Force on an object due to gravity, found using mass multiplied by gravitational field strength. Unit: newton (N). See also: Mass.

Work done

Energy transferred when a force moves an object through a distance. Unit: joule (J). See also: Power.

Practise using these in the GCSE Physics quiz or read the GCSE Physics revision guide.

Part of the GCSE Physics revision set: the revision guide and self-marking quiz.