WARNING: The van der Graaff generator has the potential to be dangerous. Always make sure it is discharged before touching it.
Theory: The charge on a charged conductor resides only on the outside surface of the conductor (as long as the conductor is at electrostatic equilibrium).
Description: Put the ice pail on the insulating stand, and connect it to the van de Graaff by means of an alligator-to-alligator lead duct taped to the van de Graaff and the inside of the pail. Make sure you have good contact. Position the balls so that one hangs just below the lip outside the pail, and the other hangs at the same height inside. Both should be a couple of cm from the pail. Switch on the van de Graaff, running around 40. As the pail charges, nothing happens to the inside ball, but the outside ball is first drawn to the pail by induced charge, and then, after contact with the pail, is repelled. Set up properly, the ball will bounce back and forth, making a satisfying clanging sound each time it hits the pail.
Setup time: 20 minutes.
References: (available in the demo room)