Well, last time I left you with a challenge. If you have two metal rods (straightened paper clips) and one of them is magnetized, how to you find out which is which, without using anything else? To find out, you will need:

- steel wool
- a sheet of paper
- the two paper clips we used last time (or you can make two new ones)

I know that I said you could not use anything else. The steel wool is for later, to help explain what is happening. Pick up the two paper clips and bring the ends together. They should stick if they are still magnetized. OK, so which one is the magnet? To find out, we need to do something different. Bring the end of one paper clip near the middle of the other paper clip. Does it stick? If it does, then it is the magnetized clip. If it does not, then bring one end of the other paper clip to the middle of that one. The magnetized clip will stick to the middle of the nonmagnetized clip. The nonmagnetized clip will NOT stick to the middle of the magnetized one. Why?

Place the magnetized clip on a sheet of paper. Hold the steel wool over the clip, grab the two ends of the wad of steel wool and rub them against each other. Tiny bits of steel wool should fall onto the paper, and you should notice that they are sticking to the paper clip. Pay close attention to where on the paper clip they stick. The ends, right? That is where the magnetic pole is, and it is where the magnetic field is strongest. The middle of the paper clip has almost no magnetic field at all, so the steel wool does not stick there.

Now you know why the nonmagnetized clip would not stick to the middle of the magnetized clip. The magnetic field in the middle was not strong enough to attract it. On the other hand, the end of the magnetized clip will stick to any part of the nonmagnetized clip.

Not at all hard to figure out, once you know the science.

This week's experiment is a fun science puzzle involving magnets. To try
it, you will need:

- a strong magnet (available at most hardware stores)
- three paper clips

Straighten two of the paper clips, so that you have two long, fairly straight
pieces of wire. Get both as straight as you can. Place one aside. Hold
the other, and rub one end of the magnet along the paper clip, starting at
your finger, and moving to the other end. Move the magnet away from the metal
and repeat the process. Keep stroking the magnet along the paper clip, always
in the same direction, for about 40 strokes. By doing this, we are
magnetizing the paper clip.

Test the magnetized paper clip by bringing one end of it near the extra paper
clip, the one that you did not straighten. If your paper clip is magnetized
enough, it should attract the other clip. If not, try again with the
procedure above.

Once you have the paper clip magnetized, you are ready for the challenge.
Put both of the straightened paper clips together. Mix them until you are not
sure which is which. The challenge is to figure out which one is the magnet
and which is not, but you cannot use ANYTHING else to test with. No fair
using the third paper clip, iron filings, a compass, or anything else. You are
also not allowed to break the paper clips. The two straightened clips are
all you need to figure it out.

So, how do you find out which is which? If I told you, you would just say,
"Oh that makes sense." instead of really trying it. If you are really
patient, you could wait until next week for the answer, but I bet you have
enough scientific curiosity to actually get the materials and try it yourself.

This week's experiment comes from a question sent to me by 10 year old Will Boyd. His question was, "If I were standing directly on the South Pole and I was holding a compass, where would the needle be pointing?"

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Open any book or web page that talks about magnets, and you will probably see a drawing that shows magnetic lines of force that extend from one end of the magnet to the other.

Are there really lines of magnetic force as they show in the drawings? Well, lets find out. To try this, you will need:

- a file
- iron nails
- a small, plastic bottle cap
- clear, dish washing soap
- a strong magnet
- metal paper clips

If you tried the experiment from the Science of Credit Cards video, don't throw away the iron filings. If you did not, then you can use the file and iron nails to make about 1/4 teaspoon of iron filings.

Fill the plastic bottle cap about 3/4 with the dish washing soap.

Then stir the iron filings into the soap, until they are evenly distributed.

Place the bottle cap on top of a strong magnet. Watch the iron filings carefully as you put the magnet in place. You should notice that the filings are attracted to the magnet.

Looking closer, the magnetic filings stick together, forming lines that look very much like the drawing in the book. So there really are lines of magnetic force, right? No.

Wait a minute! What do you mean by "No"? I can see the lines, right there in front of me!

Well, there are lines of iron filings, but there are no lines of magnetic force. The magnetic field that extends around the magnet does connect one end to the other, but it is spread evenly, not in specific lines of force. Then why do the filings line up like that? To find out, lets look at some paper clips.

Pour a pile of paper clips on the table, and put the magnet into the pile. When you lift the magnet, the paper clips stick together, forming magnetic chains.

Each of the paper clips in the chain now has a north and south magnetic pole. In the photo, the paper clips are sticking to the north pole of the magnet, so on the first paper clip, the end that is touching the magnet will be a south magnetic pole. The other end will become a north magnetic pole, attracting the next paper clip in the chain. That paper clip will also develop north and south magnetic poles, and will attract the next paper clip in the chain.

The same thing happens to the iron filings. They attract each other, end to end, to form chains, just as the paper clips did. That is what forms the lines you see, not invisible lines of magnetic force. How do we know?

Remove the magnet, and stir the soap again. Put the magnet back, and you will see the lines form again, but if you look closely, you will notice that they are not in exactly the same place. If there really were actual lines of force, the filings would line up in the same place each time. Since the magnetic field surrounds the magnet evenly, instead of in lines, the locations of the chains of iron filings are random each time. You always get the chains, but they are always in different places.

The lines in the drawings work well for explaining magnetic fields, and the chains of iron filings reinforce that idea, but when you observe carefully, there are no magnetic lines of force.

Why does putting a plastic bag over a credit card make it scan better?

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This week's experiment is the really a prelude to next week's. I wanted to do an experiment on how to kill a magnet, but before you can kill one, you need to know how to make one.

To make a magnet, you will need:

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For this experiment, we will make one of the easiest electromagnets that I have seen.

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If you have ever played with magnets, you quickly found out that each magnet has a north pole and a south pole. How would you like to make a magnet that has two north poles? You can, once you understand the science.

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Use the compass you constructed in Video 149 to explore magnetic fields, from electric wires to your kitchen cabinets.

This project has Science Fair potential

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Make a working compass from household objects.

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Attractive Cereal

They put WHAT in my cereal?

What do they put into breakfast cereal to give you your daily requirement of iron?

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This week's experiment is one that I stumbled upon while working on another idea. That seems to happen to me frequently. I was planning to magnetize a needle and as I was sorting through all the magnets on our refrigerator, I got sidetracked into playing with the rubber magnets (which are really plastic, not rubber). The more I played; the more interesting it got. To explore, you will need:

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