Here's a unique science lab which shows that bodies in stable equilibrium cannot be tipped over unless their center of gravity is raised. Demonstrate this by stacking the cylinders so the heaviest is on the bottom. If placed on a book or inclined plane, you'll have to raise the book quite high until the "tower" falls. Is this still true if you put the lightest on the bottom? Includes 4 cylinders, 1" diameter and 3/4" high - aluminum, steel, PVC, and polyethylene; steel center pin; instructions.