Study how energy and momentum change in elastic and inelastic collisions. The apparatus consists of a curved track with a base permanently mounted at one end. The track is level so the collision occurs only in the horizontal plane simplifying the calculations. On the base is a support to hold a ball at the proper height for a center to center collision with a second ball rolling down the track. A pin and three holes are provided in the track so that the drop height of the ball is consistent.