 Mean free path

The mean free path is the average distance travelled between collisions. For dilute targets with number density $n$ and effective collision cross-section ${\sigma }_c$, $\ell \sim 1/(n{\sigma }_c)$; identical-particle conventions introduce factors such as $\sqrt{2}$.

The mean free path is a concept from kinetic theory that measures the average distance a particle travels between successive collisions with other particles. This concept is commonly used in fields such as physics, chemistry, and engineering, particularly in the study of gases.