Physics key terms

A simplified diagram that represents one object as a dot or box and shows every external force acting on it as a labelled arrow.

Motion in which gravity is the only force acting on an object.

The change from a liquid to a solid.

The number of complete waves passing a point each second, measured in hertz (Hz).

A force that opposes motion between surfaces in contact.

A safety component that melts and breaks a circuit if the current is too large.

A huge collection of stars, gas and dust held together by gravity.

A detector that records gamma rays from a radioactive tracer in the body to produce an image of its distribution.

High-energy electromagnetic radiation emitted by a nucleus as it loses excess energy.

Electromagnetic radiation emitted by a nucleus as it loses energy; its emission does not change the nucleus's mass number or atomic number.

High-frequency electromagnetic radiation emitted during changes in an unstable atomic nucleus.

A state of matter whose particles are widely spaced, move constantly and randomly, and spread out to fill their container.

The tiny atoms or molecules represented in the particle model of a gas.

Force acting normally per unit area on a surface, produced in a gas by particle collisions with that surface.

Pressure measured relative to atmospheric pressure; it is zero when the pressure equals atmospheric pressure.

A toothed wheel that turns about an axle and can transmit a turning effect to another gear.

A detector in which incoming ionising radiation causes electrical pulses that can be counted.

A change in a gene that may affect how a cell functions.

A device that converts the kinetic energy of a rotating shaft into electrical energy.

The production of a potential difference across a conductor when it moves relative to a magnetic field or the magnetic field around it changes.

A model in which Earth is stationary at the centre and the Sun and planets move around it.

Describes an Earth satellite that appears to stay in the same position in the sky to an observer on the ground.

An orbit above Earth's equator that matches Earth's rotation, making a satellite appear fixed above one place on Earth.

An instrument with a metal cap, stem and thin gold leaf; movement of the leaf shows the effects of electric charge.

The change in the vertical value divided by the change in the horizontal value; on a distance–time graph, it gives speed.

A region around matter in which another mass experiences a gravitational force.

The gravitational force on each kilogram of mass, measured in newtons per kilogram (N/kg).