Physics key terms

The angle between a ray travelling into a new material and the normal.

The process in which a particle and its antiparticle meet and their mass is converted into energy; in PET, a positron and electron produce two gamma-ray photons.

A result that differs substantially from the pattern formed by the other results.

The weight indicated when an object is supported while immersed in a fluid; it is reduced by the fluid’s upthrust.

The upward force on an object in a fluid equals the weight of the fluid it displaces.

A human-made object placed in orbit around a body such as Earth.

A small, mainly rocky body that orbits the Sun.

The thin layer of air surrounding the Earth, held there by gravity.

The bending and blurring of light as it passes through moving layers of air.

The force per unit area exerted on a surface by air molecules colliding with it.

A very small particle with a positively charged nucleus surrounded by electrons.

An explanation of an atom’s structure that can be tested and changed when new evidence is found.

The number of protons in the nucleus of an atom; it identifies the element.

The number of protons in a nucleus, written as $Z$. It identifies the element.

A reduction in the intensity of radiation as it passes through matter.

To exert a force that pulls objects towards one another.

A force that pulls objects towards one another.

The detection and perception of sound by the ear, auditory nerve and brain.

The total change in velocity divided by the time over which that change occurs.

The mass of a whole object divided by its total volume, including any hollow or air-filled parts.

The total distance travelled divided by the total time taken.

The count rate measured without the radioactive source being investigated; it is the detector's reading due to background radiation.

Ionising radiation that is always present in the surroundings, originating from both natural and artificial sources.

Forces that combine to give a resultant force of zero.

An equation representing a nuclear change in which the totals of the mass numbers and charge numbers are equal on both sides.

A fundamental SI unit from which other units can be formed.

Two or more cells connected together, shown by repeated long–short line pairs.