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.