Arcs And Sparks - Testing (1980)

[Music] Do you think of electricity as something that creates arcs and sparks? The biggest arcs and sparks come from lightning, which is a natural form of electricity. Electricity could be dangerous if you did a dumb thing like this. But there are other and safer ways to learn about electricity. [Music] For example, magnetism is related to electricity. You've probably used a magnet to do things like this. The metal clips are attracted to the magnet. [Music] But magnets don't attract paper, do they? [Music] Then what would you call this force? You can't see it and you can't feel it, but there certainly is a force of some kind. It's a form of electricity known as static electricity. It's the same force that you create when you scuff your feet on a rug or a carpet in very dry weather. We can make our own static electricity with simple materials such as these. Let's conduct some tests and see what materials work best. We've seen how this plastic rod and cloth attract paper. What other kinds of rods work as well? [Music] Wow. [Music] You should try tests like this yourself. Your results might be different in some cases. Well, so far we've only tried attracting paper. Let's test some other materials. Wow, [Music] wow. [Music] Wow. [Music] There are still other materials which respond to static electricity. These are pith balls. They're cut out of the center of the stem of a woody plant. We've suspended them on threads. They first are attracted to the plastic rod, but then they seem to be repelled by it. That's surprising. Why should the balls first be attracted and then repelled by the same rod? Does the static electricity in the rod change? Or is it something about the balls? To learn more about this, let's go back to the magnets for a moment. Magnetism and electricity are closely related, although they act and come about in different ways. For example, the magnet has no effect on the pith balls. When we tested the plastic rod on these materials, the static electricity attracted all of them. When we try the magnet, the iron filings are the only material it attracts. We think of magnetism as an invisible force that attracts other metal objects. But two magnets may also repel each other. It depends on how the magnets are held as you bring them near one another. You can feel either attraction or repulsion. What do you suppose causes this? Put a paper card on top of two magnets with a thin piece of wood separating the paper from the magnets. Then sprinkle some iron filings on the card. If you sprinkle them evenly, you'll soon see that the filings form into the pattern of the magnetic field that surrounds these magnets. This pattern tells us some things about the lines of magnetic force. [Music] All magnets have poles. One is called a north pole and the other a south pole. This isn't a real pole that sticks up like a flag pole. These are just names we give to the two ends of the magnet. At one end, we find the greatest concentration of one form of magnetism. We call this end the north pole. At the other end, we find the greatest concentration of the opposite form of magnetism. We call this end the south pole. North and south poles attract each other whether they're at the opposite ends of one bar magnet or at the ends of two bar magnets as we see here. Now, let's change the position of the magnets. We can see from the lines of force that two north poles or two south poles repel each other. Now we've discovered something very important about magnets. Unlike poles such as north and south attract each other and like poles such as two north poles or two south poles repel each other. Is pairing of like and unlike poles a clue to why the pith balls are sometimes attracted and sometimes repelled by the rod? Yes, static electricity can behave either as positive or negative. In this way, the two forms of static electricity are something like the north pole and the south pole of a magnet. Positive and negative electricity attract each other. But two negatives or two positives repel each other. When we rub this rod, we are giving it a charge of electricity. A static electric charge such as we are causing can be either positive or negative depending on the materials we use. Let's say this rod has a negative charge after we rub it. At first, the balls appear to be attracted to it. However, when one of them touches the rod, the ball picks up a negative charge from the rod. Now, the rod and the ball have the same charge and thus they repel each other. Try this yourself. It's a good safe way to learn about electricity. Another safe way to find out about electricity is with a wire and a battery or dry cell. Now you're arranging for electricity to flow in a conductor in some ways as water would flow in a pipe. Do you want to prove that electricity will flow in this wire? Place a pocket compass beside the wire. This pocket compass needle is really a small floating magnet. What do you suppose makes it line up with the wire this way? When we start the flow of electricity, there are many simple and safe experiments that will help you learn more about electricity and magnetism. [Music] You can have fun learning about electricity and magnetism. And you don't have to make any sparks and arcs while you're doing it. [Music]