Attract or repel?

A street dog wags its tail at people who feed it, but barks at a dog from another street. Magnets behave a bit like that with each other: sometimes they pull together, sometimes they push apart.

In your book, two bar magnets, A and B, have their poles marked. Magnet A lies on 5 or 6 round pencils so it can roll. Bring one end of B near one end of A, without touching. Then bring the other end of B near the same end of A. One time A rolls towards B; the other time it rolls away.

The result:

• Unlike poles attract. The North pole of one magnet and the South pole of another pull together.
• Like poles repel. Two North poles, or two South poles, push each other away.

Now use an iron bar in place of one magnet. Both ends of the iron bar are attracted by both poles of the magnet. So attraction does not prove that something is a magnet: plain iron is attracted too. Repulsion does prove it, because only a magnet can push a magnet away. Reshma buys three identical metal bars: two are magnets, one is plain iron. The two bars that repel each other must be the magnets.

A compass needle is a magnet too. Bring the North pole of a bar magnet near the North pole of the needle and the needle moves away. Bring the South pole near it and the needle moves closer.

At Reshma's school fair, two little matchbox cars carry magnets with like poles facing each other. Bring them close and they move away from each other, because like poles repel.