Thus, indirectly, thermal velocity is a measure of temperature.

Since the thermal velocity is only a "typical" velocity, a number of different definitions can be and are used.

Taking to be the Boltzmann constant, is the temperature, and is the mass of a particle, then we can write the different thermal velocities:

We are interested, rather, in ensembles of atoms, at different space-points and, in many cases, with different thermal velocities.

For non-relativistic thermal velocities, the Doppler shift in frequency will be:

Both electrons and ions will stream outward with their respective thermal velocity.

If the ions are relatively cold, their thermal velocity will be small.

The thermal velocity of the electrons will be fast due to their high temperature and low mass: .

This means that the electrons on one side of the interface have a greater thermal velocity.

The random motion of charges is analogous to heat - the thermal velocity of randomly vibrating gas particles.