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)

  • $\begingroup$ 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 $\sqrt{\frac{3\pi}{8}}=1.0854$ $\endgroup$ – Poutnik May 25 at 19:42

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