One of the fun things to do with a Van de Graaff generator is to show how like charges repel.
We take a paper napkin, and cut thin strips of the lightweight paper. We then tape the ends of the paper together at one end, and tape that end onto the Van de Graaf generator.
The effect will look somewhat like long hair cascading down the soda can.
Now turn the Van de Graaff generator on. The thin strips of paper all get the same charge, and start to repel from one another. The effect is "hair raising". The strips start to stand out straight from the can, like the hair on the back of a scared cat.