Enskog and van der Waals play hockey

Abstract

We consider the mean free path of a hockey puck in a system of other pucks on an air table, and show how the simple low-density kinetic-theory value for this mean free path can be extended to higher densities. This approach is connected both with the Enskog theory of the transport properties of dense gases and with the van der Waals theory of the equation of state of dense gases. We derive several simple approximations for the high-density mean free path, and compare the results with each other, with accurate computer-simulation results, and with experimental results obtained in the freshman physics laboratory of the University of Maryland. We present the arguments in both simplified and more elaborate forms.