G

　　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 rlects 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 rerence to their present position. This point of rerence 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.

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