It may be one-dimensional, but it's a good lab for elementary or middle school students. Study elastic collisions by observing the effects of conservation of momentum and energy. Propel one or more balls down the track to hit balls grouped further down. Observe how far - and how many - in the second group move in response. Includes: 27" aluminum channel track, 5 steel balls (13 mm; 3/4" diameter); 2 molded plastic supports; instructions.