An air track is a virtually friction-less surface for demonstrating Newton's laws of Physics. It consists of a sqaure diamond prism with air blowing in at one end, and holes along the top two surfaces.

          
    (like this               (like this but 
   but squarer)                       longer)
                           ____________________
   holes--> ./\.          |. . . . . . . . . . |           _______
            /  \          |                    |__________|       |
           /    \         |____________________           |  air  |
           \    /         |                     __________| blower|
           |\  /|         |                    |          |_______|
           | \/ |         |____________________|
           ^    ^


                           _______________
      /\                  |               |
     //\\                 |               |
    //  \\  air car       |_______________|

Air from the holes blows under the car creating a cushion of air like a hovercraft making the only friction air friction which is minimal as the car is long and flat. Rubber bands are attached to the ends of the air track so that when the cars hit the end they bounce back with a close to perfect elastic collision.