Experiments in statistical mechanics

We present experiments designed to illustrate the basic concepts of statist ical mechanics using a gas of "motorized molecules." Two molecular motion m achines are constructed. The pressure fluctuation machine (mechanical inter action simulator) is a working model of two gases separated by a movable pi ston. The Boltzmann machine (canonical simulator) is a working model of a t wo-level quantum system in a temperature bath. Dynamical probabilities (fra ction of time) are measured using mechanical devices, such as stop watches and motion sensors. Statistical probabilities (fraction of states) are calc ulated using physical statistics, such as microcanonical and canonical stat istics. The experiments enable one to quantitatively test the fundamental p rinciples of statistical mechanics, including the fundamental postulate, th e ergodic hypothesis, and the statistics Of Boltzmann. (C) 2000 American As sociation of Physics Teachers.