The laws of conservation of energy and linear momentum are two of the great laws of physics which can be applied to a large number of physical problems. When we observe a collision between two objects, for example, we are tempted to assume that the collision between the objects is perfectly elastic (conserves mechanical energy as well as momentum). In practice this is often far from being the case. In general, the mechanical energy before and after a collision may be quite different. The law of conservation of linear momentum, however, is applicable during collisions because external forces can be ignored. Linear momentum is conserved even in cases where mechanical energy is not. This fact is often used to measure the masses of objects, particularly in the field of subatomic particles. In this experiment you are asked to examine the principles of conservation of linear momentum and energy by considering the motion of gliders on an air track.