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.