equipartition  of  energy , principle of According to this principle,  the average  energy  per  molecule  of a gas in equilibrium  is equally distributed between every degree of freedom*,  and  is numerically equal to (1/2) kT per degree of freedom  (k=Boltzmann constant,  and  T is the absolute temperature of the gas).

This  principle  can  be  deduced  from  Maxwell Boltzmanns classical statistical mechanics*.