Physics key terms

Radioactive material carried through the environment after a nuclear explosion or accident.

A radioactive substance introduced into the body so that its movement or concentration can be detected from outside.

Unwanted radioactive material that must be managed safely because some of it remains dangerous for a long time.

An isotope with an unstable nucleus that undergoes radioactive decay.

A radioactive isotope attached to a substance chosen to travel to, or collect in, a particular part of the body.

The treatment of unwanted tissue, such as a cancerous tumour, using ionising radiation.

A radioactive isotope incorporated into a substance so that its movement or distribution can be detected.

An electromagnetic wave in the lowest-frequency, longest-wavelength region of the electromagnetic spectrum.

Electromagnetic radiation used to carry signals for broadcasting and other wireless communications.

The distance from the centre of an object to its edge.

A radioactive gas released naturally from rocks and the ground that can enter buildings.

Variation that makes repeated measurements differ unpredictably; its effect can be reduced by taking repeats and calculating a mean.

Motion in which molecules continually move at different speeds and in changing directions.

A process whose outcome for an individual event cannot be predicted with certainty.

The difference between the largest and smallest values in a set of measurements.

The span from the lowest to the highest value of a variable tested or measured.

A region of a longitudinal wave where the particles of the medium are further apart than usual.

How much a quantity changes per unit time.

Change in a quantity divided by the time taken for that change.

The change in momentum divided by the time taken. This is equal to the resultant force acting on the object.

The change in speed per unit time; a positive change is acceleration and a decrease in speed is deceleration.

The decrease in temperature per unit time; it can be used to compare how quickly samples cool.

The amount of thermal energy transferred each second from a warmer object or place to a cooler one.

A comparison of two quantities, such as the numbers of teeth on two gears or the lengths of two lever arms.

The scientific reason for carrying out an investigation in a particular way.

A line showing the direction in which a wave travels.

A two-dimensional drawing that uses straight, directed lines to represent the paths taken by light.