In this example, the key point is that the kinetic energy is quadratic in the velocity. The equipartition theorem shows that in thermal equilibrium, any degree of freedom (such as a component of the position or velocity of a particle) which appears only quadratically in the energy has an average energy of 1 ⁄ 2 k B T and therefore contributes 1 ⁄ 2 k B to the system's heat capacity. This has many applications.