this post was submitted on 17 Apr 2024
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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?

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[–] [email protected] 9 points 4 months ago (1 children)

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

[–] [email protected] 1 points 4 months ago* (last edited 4 months ago) (2 children)

Why wouldn't the electrons go to ground through your body while you're touching it?

[–] [email protected] 2 points 4 months ago

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.

[–] [email protected] 1 points 4 months ago (1 children)

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.

[–] [email protected] 1 points 4 months ago (1 children)

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?

[–] [email protected] 1 points 4 months ago (1 children)

If the generator is running, it's still adding more charge, so you will be instantly at different potentials

[–] [email protected] 1 points 4 months ago (1 children)

I see. Would there also be an arc if you put your hand near the generator while it was running, then?

[–] [email protected] 2 points 4 months ago

As long as the potential is great enough to break down the dielectric of air yes.

[–] [email protected] 4 points 4 months ago (1 children)

I am not expert, but seems plausable. Shock comes from high voltage electric charge jumping from metal to skin. If you press it, you are part of the electric charge. If you are far away, charge cannot jump. Problem is only when you are couple of centimeters close to it. AFAIK, this is not current, but electric discharge, I think it cannot kill you (it is just very unpleasant), but maybe someone else knows better?

[–] [email protected] 1 points 4 months ago (1 children)

Thing that confuses me is that when you let go, you should have the same charge as the generator. No charge difference, no arc. Unless I'm wrong about something, which I probably am (hence my confusion).

[–] [email protected] 3 points 4 months ago (1 children)

The generator is generating a difference. Even if you have the same potential when you're holding it, as soon as you let go, that ends.

[–] [email protected] 1 points 4 months ago (1 children)

Does the human body rapidly discharge into air or something?

[–] [email protected] 1 points 4 months ago

Enough for a change in potential to cause arcing, as we can see. I'm sure you could find relevant experimental studies, or even conduct them on yourself with a proper transformer and voltmeter.

[–] [email protected] 2 points 4 months ago

Yeah, if you move your hand around on those things you'll get a static shock, it's going to hurt, but it won't kill you. If you watch those demonstrations they have a pole they ground the generator out with.

[–] [email protected] 0 points 4 months ago

If you're in some kind of science experiment where you're being conditioned to not stop touching something: Yes.