Entropy Pennies
A tray is filled with pennies painted green on the tails and red on the heads. If the tray is shaken the pennies begin to flip at a rate dependent on the magnitude of the shaking. Eventually an equilibrium is reached, with approximately equal numbers of reds and greens. Further shaking will not, of course, return them to their original state. If only a few pennies are used, they will occasionally return to their original state, showing the dependence upon the number of particles in the system.