Consists of a spring-loaded mechanism that fires a brass ball, a pendulum, and a curved scale. The pendulum has a catching mechanism which catches the brass ball, and a ratchet on the bottom. When the pendulum catches the ball it starts the end of it starts travelling along the curved scale. The ratchet on the bottom of the pendulum only allows the pendulum to progress one way up the scale, causing it to come to a standstill as soon as it starts swinging back towards the starting position.
If you want to perform an actual measurement of the kinetic energy or velocity of the ball, this can be done too. The mass of the ball and the mass of the pendulum are noted on the base of the demo. The only detail you need in addition to that is the height of the scale relative to the resting height of the pendulum, since the scale starts from zero.
Wikipedia Article on Ballistic Pendulum: http://en.wikipedia.org/wiki/Ballistic_pendulum
Demo room information