Fun with Static Electricity!
Let's have some fun with static electricity! Simple experiments illustrating the fact that opposite charges attract and like charges repel.
Announcer: Frostbite Theater presents... Cold Cuts! No baloney!
Joanna and Steve: Just science!
Steve: It's called an accelerator because we're trying to speed something up.
Steve: It's called an electron accelerator, so what are we speeding up?
Steve: Yeah! In our machine, we grab electrons. We rip them off of atoms, which is not that hard to do. Shove them in the accelerator. The accelerator is a machine shaped like a racetrack. It's about a mile around. Only job: take electrons, speed them up.
We take the electrons, we speed them up to about the speed of light, which is 186,000 miles a second. If you could run at the speed of light, you could run around the earth seven and a half times in a second. So, the speed of light's moving really fast.
And then, to study atoms, what you do...
Take a lump of the junk you want to study...
Take these electrons moving at about the speed of light, and you smack them into each other. Yeah, pretend you're an atom. Okay, you're sitting there, you're talking to your atoms friends, minding your own atom business... And some scientist comes along and throws an electron at your head, moving at about the speed of light. What's your head gonna do?
Steve: Yeah, you're head's gonna pop off. Right? It's going to flying across the room, splatter against the wall, be kinda gross.
What's the electron gonna do? It's gonna hit my head and then...
Steve: Bounce somewhere. Right? It's going to go somewhere else. So, maybe instead of going directly behind me, maybe the electron bounces that way while my head flies off that way. Okay, that's how we study atoms here. We throw things at them. And then we look to see where the bits and pieces go. And, by studying where the bits and pieces go, we can figure out how it was put together.
Now, our machine that does this for us, our accelerator, only works because, opposite charges attract and like charges repel. Right? We use electrons. What do electrons have that are different than, say, protons or neutrons?
What charge do they have?
Steve: They're negative! Right. And, since they have a charge, we can push them around. So, if you have an electron sitting here that's posit- that's negative and you want it to go that way, what can I put in front of it?
Steve: I put a positive charge in front of it. Because, what do opposite charges do?
Steve: They attract. Or, what can I put behind it?
Steve: Another negative. Because, what do same charges do?
Steve: They repel. Right. And that's what our accelerator does. We arrange it so that the electrons passing through that we're trying to push always see a negative in back - a negative charge in back of them and a positive charge in front of them. So they get pushed through our machine and sped up.
And, again, it works because our machine gets the timing right, and it works because opposite charges attract and like charges repel. Who in here believes that opposite charges attract and like charges repel?
Like, three people.
Who must see it, or you refuse to believe it?
Okay, I can get behind that. That's more like science. I can try to show you... with this. What is this?
Audience: I have no idea.
Steve: Not a piece of tape.
Steve: Not a piece of plastic. This is a very expensive piece of scientific equipment. It's called an electroscope. And it's made from a little clippy thing. And not a piece of plastic. It's made from two pieces of plastic.
We have spared no expense for your education, right? Two pieces of plastic!
So, what I can do... I can take my finger and I can scrape it on the plastic sheets. Electrons will get ripped off of me. They'll pile onto the plastic. If one piece of plastic gets extra electrons on it, what charge will it have?
Steve: Negative! If the other piece of plastic also gets extra electrons, what charge will it have?
Steve: Negative! If I get negative next to negative, what'll they do?
They'll repel! Right? Like that.
Okay, so negative here, negative here. Same charges. They try to spread apart.
In my pocket I have a pen. If I put the pen between the plastic sheets, what will happen?
All right? Kind of a boring experiment.
Ahh, over here, I have a nail. Put the nail between the plastic sheets, what'll happen?
Audience: Nothing. We don't know.
Steve: Yeah, now it jumps to it.
Steve: Yeah! So how come it jumps to the nail but not the pen?
Steve: Nail is metal, pen is...?
Steve: Plastics make good...?
Steve: Insulators! Right! For electricity, that means the electrons in the pen can't move around all that well. So if I have extra electrons on the plastic sheets, I shove the pen in there... The extra electrons are pushing on the electrons in the pen. Electrons in the pen are trying to get away. But they can't move. It's an insulator so they're stuck so nothing really happens. The nail, though, made from...?
Steve: Which is a good...?
Steve: Good conductor. That means the electrons can move around. So if I have extra electrons on the plastic sheets, I shove the nail in there... The extra electrons push on the electrons in the nail. Electrons in the nail want to get away. And, since they can move, they do. They back off. What stays behind? What can't move in the nail?
Audience: The protons.
Steve: Yeah, the atom. Right? The atoms are stuck. So, if you're an atom. You're stuck. And one of your electrons runs off screaming into the night in that direction, what charge do you get?
Steve: Positive. Right. If I lose a negative, I become a positive. So the negatives back off. This becomes positive. This is negative. Those are opposite charges and opposite charges attract. Right.
How about me? Am I a conductor or an insulator?
Steve: How can I test? Put my finger in it. Yeah. If I put my finger in there, if I'm an insulator, what'll happen?
Steve: Yeah. Nothing. If I'm a conductor, what'll happen? It'll jump to me. Yeah.
Yeah, I'm a conductor. I'm not a great conductor, but I'm a good enough conductor electricity will flow through me.
What happens if a lot of electricity flows through me?
Audience: You die.
Steve: I die. What do they call that?
Steve: Yeah, it's called electrocution.
One group said 'funny.' It's not called 'funny.' It's called electrocution.
And, the reason why I'm slightly worried about electrocution is we're going to play with this thing. This is called a Van de Graaff generator, named after Mr. Van de Graaff. And, it's basically a person walking across the carpet machine. How many of you have ever walked across the carpet and then you touched a doorknob or your kid sister, or something like that, and there was a spark? Why's it do that?
Audience: Static electricity.
Steve: Yeah. If I walk across the rug, what can I grab off the rug? I can grab electrons off the rug. And they pile up on me. And, it's nothing personal, but if I get a lot of extra charge on me it's going to try to spread out and go somewhere else where's there's more room. And if my kid sister happens to be sitting there, you know, maybe I can give her some of the electrons. I'm just sharing. I'm not trying to shock her or anything.
Umm, and that is kinda what this thing does. There's a motor inside of here. And, when I turn it on, it makes this belt go around and around and around. And, that's like a person walking on the carpet. It's gonna dump electrons onto this dome.
If this dome gets one extra electron on it, does it care?
Steve: No! It's just one, so so what. What if I get two? Side by side. What will they do?
Audience: Spread apart.
Steve: Negative next to negative.
Steve: They're going to repel. Right, they're going to get as far apart as they possibly can. I don't know where, exactly, they'll go. But they'll spread out as best they can.
What if I get three?
Audience: Spread out.
Steve: They're going to spread out as best they can. What if I get, like, a billion? Sooner or later, what's gonna happen? Sooner or later I'm going to get too many charges, too small a space, they want to spread out to the largest thing around. What's the largest thing around?
Steve: No, not me. I'm not the largest thing around.
Audience: The air. The earth.
Steve: Big round thing.
Audience: The earth. The earth.
Steve: The earth!! The planet! It wants to get into the earth. I'm not larger than the planet, thank you very much.
Right, it wants to get into the earth in part because there's a lot of room. Plenty of space to spread out. And partly because that's where these electrons are coming from in the first place.
When we do this, we're not making new electrons. We're just moving them from one place to the other. So, what we're basically doing is reaching into the earth, grabbing some electrons, and then plopping them up here. And then for everything to balance out again, that same number of electrons needs to get down to the earth.
So, to help them get there, we have a second dome. Connects with a wire. And, if you were to trace it... it comes out of the plug here. This part of the plug, which is called the ground. Why is that called the ground?
Audience: Because it's the ground.
Steve: 'Cause it goes to the ground. Right. If you were to trace this through the building, you would find out that it literally goes into the earth. So this gives the electricity a nice way to get into the planet instead of through some other conductor standing nearby such as...?
Steve: Me! Yeah! I'm on the ground. I conduct. It could try to go through me to get there. That could be bad. So we give it an easier way. And hopefully it picks the easier way and not the way that ends up going through me.
So... What will it look like... if charges are able to jump from one dome to the other?
Audience: Fire. Lightning.
Steve: Like, what's electricity look like? Like lighting? Okay. Let's find out.
Now, first we want to hear is like a little crackly sound. Ooh! A little crackly sound! Then we're gonna sneak up on it with the other dome.
Van de Graaff: Snap!
A Single Startled Audience Member: Aaah!
Van de Graaff: Snap!
Steve: Tell you what. We can see it better, if you don't freak out, and if we turn the lights off.
Van de Graaff: Snap!
Steve: What's it look like? Little bit like baby lightning. And it's making little baby thunder.
Lights back on, please.
Van de Graaff: Snap!
Steve: Why is it making little baby thunder? How does lightning make thunder? The lightning jumps through the air and then it...?
Heats up the air. This little spark is actually hotter than the surface of the sun.
So it jumps through the air, and heats up the air, the air expands, and then it bumps into the neighboring air. And then that makes the shockwave that we hear. But how come in a thunderstorm, you see the lightning... ...and then you hear it, but right now we see it and hear it at the same time?
Audience: 'Cause light's really fast.
Steve: Yeah, light's faster than sound. In the room, the light still gets to you first. But the gap in time between the light reaching you and the sound reaching you - it's just too small to notice that there's a gap. If you were to back-up, sooner or later you'd get far enough away that you'd begin to notice "Ooo! Now I see it!" and "Now, ooo! I hear it!"
Aah, so, in a real thunderstorm, lightning strikes, five seconds go by, then you hear it, how far away?
Audience: A mile.
Steve: Yeah, about one mile. Takes sound about five seconds to travel one mile. So that's a pretty close strike.
You'll also notice when the domes are far, sparks are big, but the gap in time between each spark is also kind of big. If I get them closer together... smaller sparks, but they happen sooner. Why does it take less time to spark when they're close, but more when they're further apart? Further apart, what's there more of between the domes?
Not space. We'd all be dead.
Steve: Air! Yeah, air's a pretty good insulator. And when there's a lot of insulation between the domes, hard jump to make. I need to get a lot of extra electrons before they can jump across that big gap. So it takes me longer to get the right number. I get them closer together... not as much of a gap. Easier jump to make. I don't need as many electrons, so I get the right number sooner. So the sparks can happen faster.
What would happen... if the domes were to touch?
Audience: It would explode.
Steve: It would explode?!
Steve: Should we try it?
Steve: That went south really quick. Well, let's aaah...
Audience: Do it!
Steve: UUUUAGH! Nothing.
Why does nothing happen?
How much insulation?
Steve: There's no insulation. Nothing stops the electrons from going from here to here, so they don't stop. They get on this dome, they walk to the other dome, go through the wire and into the ground. Soon as I pull them apart, then there's a gap they need to bridge. So they need to build up until enough of them could jump across to the other one. So let's try a couple of things.
Audience: Styrofoam! Marshmallows!
Steve: Not marshmallows.
Audience: Styrofoam! Packing peanuts!
Steve: Yeah. Little bits of styrofoam. Little bits of styrofoam in a bowl, which is nice. But, weirdly, the bowl has a suction cup on the bottom. Which is weird. But, it's nice for us, because we can take the bowl... and stick it to the dome, thusly. And then we'll turn it on.
What's gonna happen?
Audience: They're going to fly around.
Steve: Why're they gonna fly away?
Audience: Because static electricity.
Steve: Trace this out for me. Turn this on, what gets on here?
Steve: Electrons. If I get electrons next to electrons, what do they try to do?
Steve: Try to spread out. So some of them spread out to the bowl. Some get in the bowl. Some get on this. Some get on this.
If this little piece of foam has extra electrons on it, what charge will it have?
Steve: If this has extra electrons, what charge will it have?
Steve: Get negative next to negative, what do they do?
Steve: Repel. If the whole dome is negative, what do they do to it?
Steve: Repel from that, too. Let's find out.
Fly! Be Free! Go!
Audience: Ooooooh! It's snowing!
Steve: Not too bad. Let's try something else.
What..... is this?
Audience: I can't really see.
Steve: Yeah, it's string. It's like.... fake hair. It's like really bad weave. And it's on a suction cup. Which, again, is weird. But, it's nice for us because I can stick it on here, thusly. And then we'll turn it on. What's going to happen?
Audience: Static electricity.
Steve: Yeah. I mean, same reason that we had for the foam. Right? I'm going to get charge on here. It's going to try to spread out. It's going to get on the string. All the strings become negative. They'll repel each other. Ahh, but unlike the foam, they're tied down, so they can't fly around the room and make a big mess on the floor.
Not too bad. Now... what will the fake hairs do if I get the grounding dome close to them?
Audience: They'll just fall.
Steve: They attract to it. Why are they attracted to it?
Audience: Because they have a lot of electrons.
Steve: If those are negative and they attract to this, then what's this?
Steve: How'd this get to be positive?
Audience: 'Cause it is.
Steve: Right? It's sitting here minding its own business. Why is it positive?
Steve: If you're an electron over here, what do you see over there? I see a bunch of negative. If there's bunch of negative over there and I'm an electron over here that's negative, what do I want to do? I want to get away from that thing. Can I get away from that thing? Yeah! Where do I go? Through the wire and...
Audience: In the ground?
Steve: into the ground. What stays behind?
Steve: Yeah, the atoms. This is just like the nail. Right, the atoms are stuck. The electrons back off. So this becomes positive. This is positive. That's negative. They're opposite charges. And opposite charges attract.
What if the domes touch?
Audience: They'll just fall.
Steve: What will the string do?
Audience: They'll fall! They'll fall!
Steve: They'll Fall! Yeah! Because there's no charge on the dome. Take it away, it goes back up. Let them touch, go back down. Want to do jumping jacks, make it do jumping jacks, kinda like that.
Now, what would happen if a person were to touch it?
Audience: Umm, they'd get electrocuted.
Steve: Or, maybe a better questions is "Should a person touch it?"
Steve: Well, maybe yes. Maybe no. Let's think this through for a bit.
Do you know...
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