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  • I hate that!

  • Why do you get shocked sometimes when you get out of your car?

  • Or when you touch a doorknob?

  • Or when you take off a sweater and hug someone?

  • And is there a way to not get shocked?

  • To prevent this from happening, you have to figure out what's happening.

  • So, this is called a Van de Graaff generator.

  • I use it a lot in science demos for kids.

  • It's a machine that builds up a ton of static charge - that is, a bunch of positive charges on the outside of this metal sphere, so that when I bring this smaller grounded metal sphere close to it, it discharges through the air in a giant metal spark that will shock you.

  • Ugh, I hate that.

  • The kids love it.

  • So, this is where it gets fun.

  • If I put a metal pan on top of the Van de Graaff generator, it should take on the same positive charge as the sphere because it's conductive.

  • But like charges repel.

  • So, when I turn this on, the pan should... fly off.

  • And it does.

  • Now, one kid saw this and asked what would happen if we put the Styrofoam ball she was holding on top of the generator.

  • Let's try it.

  • But I told her probably nothing would happen, because Styrofoam is an insulator.

  • So, I assumed there's no way you can pass charge to it.

  • Let's see.

  • I stood there confused.

  • Insulators don't conduct electricity, right?

  • So, how can you charge them?

  • Well, in fact, it's very easy.

  • This balloon... is now charged.

  • See?

  • And this tape is now charged.

  • See?

  • And these are both insulators - just not perfect insulators.

  • In very violent events, electrons from the atoms in one material can get stripped off and passed to another material, causing both materials to become charged, this one positively, because it lost electrons, and this one negatively, because it gained electrons.

  • Even if they're usually insulators, and for the poor tiny atoms in these materials, rubbing them together would definitely be considered an unsettling violent event.

  • Now, back to the car.

  • The violent event here is when you get out of the car, you slide across the seat, and both you and the seat become charged.

  • And now some of that charge will leave your body into the air.

  • But if the air is cold enough and dry enough, and you touch the metal soon enough, that charge will quickly leave your body into the metal, and you will feel that.

  • And you'll hear it, too, as a shock.

  • So, how do you prevent this from happening?

  • Well, don't keep yourself isolated.

  • As you get out of the car, touch the metal on the side of the car.

  • And even if charge is building up on you, it'll continually flow into the metal, and it won't build up enough on you to shock you.

  • Problem solved.

  • Either that, or rub yourself all over with dryer sheets.

  • I don't know if that works.

  • Someone please try it and let me know.

  • So, now for this insulator, there was no violent event.

  • Or was there?

  • See, air is usually an insulator, too, which is why you're not shocked by your outlet until you stick metal in it.

  • Air is an insulator until the voltage, which is related to the amount of surface charge on here, gets so high that electricity can travel through the air.

  • Electrons are stripped off of the air molecules along the way in a process called ionization, which releases light, and you see a spark.

  • But you have to get the voltage really high for this to happen, so high that overcomes the insulating properties of air.

  • So high that it overcomes the insulating properties of Styrofoam, and the Styrofoam takes on a surface charge that repels the metal sphere.

  • Large enough for the insulating plastic on this pom-pom to repel itself, so that they stick up - at least on the top.

  • On the bottom, there is more going on where the pom-pom sticks to the sphere, and it has to do with electrical induction.

  • But we'll leave that for another video.

  • Thank you so much for watching.

  • I'm going to see if I can get my hair to stand up, if there's not too much moisture.

  • Although it rained today, and it's pretty warm.

  • Nothing's happening.

  • It's too humid, and this thing's not big enough.

  • It's going to shock me.

  • Ah!

  • It didn't!

I hate that!

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B1 US metal charge sphere styrofoam air shock

Avoid electric shock getting out of a car!

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    Shinichiro posted on 2019/12/18
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