
Maxwellian speed distribution
Fig. 3.1 . The Maxwellian probability distribution of speed density (left axis) at different speeds, v (bottom axis) for a temperature of T = 218.85 kelvin and four noble gases, helium (blue), neon (yellow), argon (turquoise) and xenon (purple). The peak of each curve occurs at the most probable speed, vP = (2kT/m)^1/2, where Boltzmann’s constant k = 1.38 x 10^23 Joule per kelvin, T is the temperature, and m is the element’s mass. This distribution was derived by teh Scottish scientist James Clerk Maxwell (18311879) in 1873. As indicated in this plot, the peak shifts to higher speeds at lower mass provided the temperature is unchanged, for less massive elements tend to move at faster speeds. A similar change occurs at higher temperatures for a given mass.
Copyright 2010, Professor Kenneth R. Lang, Tufts University

