In kinetic molecular theory, the average velocity of gas particle is zero since the molecule move in different directions, and the overall effect is zero. Howeever, you can calculate different speeds.
Specifically, RMS (Root Mean Square) speed is the speed of a particle in a gas with the average kinetic energy. This is $$u_{rms}=\sqrt{\frac{3RT}{M}}$$
Conceptually, if $v_1, v_2,...,v_n$ are the speed of $n$ particles in a gas, the RMS is
$$u_{rms}=\sqrt{\sum\frac{v^2_i}{n}}$$
As the Wikipedia page on RMS points out, RMS is a special case of standard deviation when the mean is zero. Hence:
- Is it correct to say that $u_{rms}$ is the standard deviation of the magnitudes of the velocity (not speed).
- If it is correct, is there any significance/use of this interpretation?