Thermal speed ($v_{\mathrm{th},s}=\sqrt{2T_s/m_s}$)

A characteristic random particle speed. Here temperature $T_s$ is measured in energy units, and the factor-two convention makes a Maxwell-Boltzmann distribution proportional to $e^{-v^2/v_{\mathrm{th},s}^2}$. Other conventions, such as the one-dimensional standard deviation $\sqrt{T_s/m_s}$, differ by fixed factors.