The simulation shows a gas confined in a cylinder with a movable piston. Initially the piston is moving left. The atoms strike piston and exert a force on it toward the right. This force causes the piston to slow down and stop. Note, that the force of the gas on the piston and the piston΄s displacement are in opposite directions, so the gas does negative work on the piston. Observe the values of the piston΄s kinetic energy and the kinetic energy of the gas.