# Collision frequency of ideal gas and velocities of molecule

Is collision frequency of gas molecule $$= \frac{V_{RMS}}{\lambda}$$ where $$\lambda$$ is mean free path. Shouldn't it be $$\frac{V_{average}}{\lambda}$$?

(I often see that in theories books suggest that frequency is average velocity/$$\lambda$$. but in solutions the same book uses RMS velocity instead of average)

• There should be used the term speed, as average velocity is a zero vector. There are also used terms mean quadratic speed and mean linear speed, with ratio $\sqrt{\frac{3\pi}{8}}=1.0854$ – Poutnik May 25 at 19:42