Explain why a scientist who planned to touch the dome of a Van de Graaff generator might be wearing rubber-soled shoes and standing on a plastic mat.
A Van de Graaff generator is a kind of a cool electricity machine that uses static to get its power. There is a belt inside of the machine that is turning at a high rate of speed, thus creating the static. The ball at the top is where the charge is held. That's a simple explanation of it, but it's about right.
If you were to touch the ball of a Van de Graaff generator (depending on its size) you would be injured or killed. The charge would go through your hand and out your feet in order to reach the ground. If you touched it with both hands you might get the added bonus of it going across your body and blowing up your heart (so to speak.)
The idea of wearing the rubber shoes and standing on the plastic mat is for insulating purposes. The less attractive you are as a conductor of electricity the less that electricity is going to head through you to ground. That's not to say that it won't, but depending on how big of a generator you're talking about it might be enough to insulate you.