5. Single particle trajectories
To get a more intuitive understanding of the effect of gravity on the gas we can track a single particle as it collides with the bottom of the container, moves unimpeded through the gas, and then collides with the top. Recall that ideal gas macroscopic behavior is consistent with a microscopic model where collisions between gas particles are rare, and therefore considered to have negligible effects. This is, of course after the gas has thermalized and reached equilibrium. During the approach to equilibrium both inter-molecular (gas) and collisions with the solid container walls distribute energy and momentum. In equilibrium the gas behaves as if it were composed of N non-interacting particles whose momentum alone is altered (only) by collisions with the container.