The probability that the system will be in a given state of motion is predicted by Maxwell–Boltzmann statistics to be proportional to exp ⁡ ⁡ ( − − U / k B T ) , where U is the energy of the system, k B is the Boltzmann constant, and T is the absolute temperature. This energy is equal to the sum of the kinetic energy ( m v 2 / 2 for a particle with mass m and speed v ) and the potential energy.