I seem to remember as a young child being told that it is safe to touch a Van de Graff generator (for the hair demonstration), but that if you let go before it is safe you will get a nasty shock. I know a bit more about electricity now, and I’m a little skeptical now. Is it possible to get a shock from letting go of something?
You get a shock when there is a big protentional energy difference between your body and something else. Either high or low.
So the “let go before its safe” means they want to stop the generator, and ground it, so the electrons leave though a path that isn’t your body, to avoid the shocks
Why wouldn’t the electrons go to ground through your body while you’re touching it?
They can and do, but you feel the zap when there’s an arc. If there’s current moving though your body without an arc, it feels like your muscles vibrating or cramping, depending on whether it’s AC or DC, mostly. After all, your muscles are activated with electrical signals.
Usually for a Van de Graf demonstration The person touching it has some level of electrical isolation from the ground. Be it their shoes or something else. If they were touching the ground directly or a piece of metal they would constantly be passing the electrons through and they wouldn’t get that whole hair raising effect.
Okay, so you’re insulated from ground. The generator charges you up. You are at the same charge as the generator. You let go of the generator. Why is there a potential difference?
If the generator is running, it’s still adding more charge, so you will be instantly at different potentials
I see. Would there also be an arc if you put your hand near the generator while it was running, then?
As long as the potential is great enough to break down the dielectric of air yes.