An air track is a scientific device used to study motion in low friction environment. Its name comes from its structure: air is pumped through a hollow track with fine holes all along the track that allows specially fitted air track cars to glide relatively friction-free. Air tracks are usually triangular in cross-section. Carts which have a triangular base and fit neatly on to the top of the track are used to study motion in low friction environments.
The air track is also used to study collisions, both elastic and inelastic. Since there is very little energy lost through friction it is easy to demonstrate how momentum is conserved before and after a collision. The track can be used to calculate the force of gravity when placed at an angle. 
It was invented in the mid-1960s by John Stull and Frank Ferguson.