File:Translational motion.gif

Summary
Translational motions—the randomized thermal vibrations of fundamental particles such as atoms and molecules—gives a substance its “kinetic temperature.” Here, the size of helium atoms relative to their spacing is shown to scale under 1950 atmospheres of pressure. These room-temperature atoms have a certain, average speed (slowed down here two trillion fold). At any given instant however, a particular helium atom may be moving much faster than average while another may be nearly motionless. Five atoms are colored red to facilitate following their motions.

Whereas the relative size, spacing, and scaled velocity of the atoms shown here are accurately represented, atoms don’t really move in 0.062-nm-thick windows; in a 3-D box, they would actually pass in front of and behind each other and collide much less often. However, the rebound kinetics of elastic collisions are accurately modeled and, if the velocities over time are plotted on a histogram, generates a perfect Maxwell-Boltzmann distribution curve.