Fun with a Van deGraff Generator

In my physics classes this month we are talking about electrostatics and electricity.  There are several awesome demonstrations involving these topics.  One is the Van deGraff Generator.  If you haven't had a chance to see a Van deGraff Generator in action you are definitely missing out.

A Van deGraff Generator has a motor, that when turned on, turns a belt.  The belt carries free electrons and dumps them onto the metallic sphere that you see sitting at the top of the image.  If you bring your hand close to the sphere you will receive a small shock as the built up charge in the sphere transfers to your body. This is very similar to shuffling your feet on a carpet and shocking someone with your finger.  

One cool demo with a Van deGraff Generator is to place several small tin containers on top of the sphere.  When you do that and then turn on the Generator you see something very cool as shown in the video below.

As you can see, the small tins fly off the Van deGraff Generator one by one!  So what's going on here?  Once electrons build up on the sphere they transfer to the first tin, then to the second tin, then to the third tin, and so forth, until the electrons reach the last tin.  Since like charges repel, there are enough charges building up between the tins that the electrostatic force that the second to last tin exerts on the last tin is large enough to lift the last tin up into the air.  The process repeats until all tins are gone.  A very cool experiment and a hit with students.