Law of statistical mechanics stating that, in a system in thermal equilibrium , on average, an equal amount of energy is associated with each independent energy state.
It states specifically that a system of particles in equilibrium at absolute temperature T will have an average energy of 1 2 k T , where k is the Boltzmann constant , associated with each degree of freedom. For example, an atom of a gas has three degrees of freedom (its three position coordinates); therefore, it will have an average total energy of 3 2 k T .