Maxwell found theoretically the probable speed distribution for a large number of molecules confined to a box undergoing random elastic collisions. In this dynamic realization, we give all the molecules the same initial speed, but random initial positions and directions. They move to Maxwell's predicted distribution pretty quickly! The top bar graph on the right is the instantaneous speed distribution, the one below averages over recent distributions.
Clicking on the "theoretical" button reveals Maxwell's prediction--slightly adjusted for a two dimensional world (so the low energy end linear rather than parabolic).