The average velocity of a particle in a gas of particles that is associated with the thermal energy. In the kinetic theory of gases it is possible to calculate the thermal velocity, with this velocity v being given by v=(3kT/m)^½, where k is the Boltzmann constant, T is the absolute temperature, and m is the mass of a particle in the gas. Strictly speaking, ‘thermal velocity’ is a misnomer, as velocity is a vector quantity and therefore has direction. See also thermal energy.