Gamma decay

A form of radioactivity where an excited atom releases a photon of gamma radiation, thereby returning to a lower energy state. The atomic structure itself does not change in the course of gamma radiation.

Gamma ray

An electromagnetic wave of very high frequency.

Gold foil experiment

An experiment by Ernest Rutherford that proved for the first time that atoms have nuclei.

Gravitational constant

The constant of proportionality in Newton’s Law of Gravitation. It reflects the proportion of the gravitational force and , the product of two particles’ masses divided by the square of the bodies’ separation. N · m2/kg2.

Gravitational Potential Energy

The energy associated with the configuration of bodies attracted to each other by the gravitational force. It is a measure of the amount of work necessary to get the two bodies from a chosen point of reference to their present position. This point of reference is usually chosen to be a point of infinite distance, giving the equation . Objects of mass m that are a height h above the surface of the earth have a gravitational potential energy of .

Ground state

In the Bohr model of the atom, the state in which an electron has the least energy and orbits closest to the nucleus.