Ever hear a magnet crackle? Neither have I.
What do we mean by ``crackling noise'' in magnets? Paper makes crackling
noise when we crumple it into a ball. As we squeeze it, it crumples in a lot of jumps,
some big, some small. Each jump is where a small part of the paper bends
or jumps into a new place, and gives off a single crackle sound.
If squeezing paper makes it crackle, what do we do to a magnet to make
it crackle? We magnetize it!
Get a magnet and some paper clips. (The magnets
used to hold lists on refrigerators are often very strong.) Can you pick up paper
clips with the magnet? Can you pick up the paper clips with other paper clips?
Most paper clips are made of iron. Magnets pull on things made of iron.
Now, rub a paper clip with the magnet. Can you pick up other paper
clips with it now?
The iron in the paper clip can become a magnet too: the paper clip is
magnetized by rubbing it with the magnet. It doesn't magnetize
all at once though: when you rub it longer, it gets more magnetized
picks up other paper clips better and better.
Did you listen carefully when you were rubbing the paper clip? I bet you still
didn't hear any crackling noise!