Where did you get the big globe? What is it called?
The machine is a Van de Graaff generator, named for its inventor, Robert Van de Graaff. We bought ours (we have four of them) from a scientific supply company. They are very cool machines. Do you agree?
Why did the big rubber band break? Did electricity cause the break?
There are two things that make the belts break. One is friction. The belts run for a long time quite fast over the rollers and this makes them wear out, and has nothing to do with the electricity.
The other thing is a direct result of the electricity. There are tiny sparks inside the machine all the time. These sparks form a chemical from the oxygen in the air called ozone. Ozone is a strong chemical, and it attacks rubber, breaking it down and weakening it. This happens to all our rubber belts sooner or later and we have to replace them. The used, broken belts are usually pretty crumbly when we take them out of the Van de Graaff generator.
Why did you turn the machine on and off with the stick?
This is an EXCELLENT question! The stick we used is made of plastic, which doesn't conduct electricity. The switch is on the base of the machine, which is separated from the ball by a plastic column. The plastic column is also an insulator and doesn't conduct electricity. When the generator is running, electrons are pulled from the base and added to the ball. This gives the base and the ball opposite charges, and it can be a lot of electricity.
Working with and around the generator builds up a charge on the operator, and touching the base often gives us shocks. Using the insulated stick helps prevent some of those shocks because it doesn't conduct electricity. We aren't really touching the switch. It is a matter of avoiding getting another shock. We get enough doing this demonstration as it is.
