Finding north with a magnet

Tie a thread around the middle of a bar magnet so that it hangs balanced and can turn freely. Give it a gentle turn, let it come to rest, and mark where its two ends point. Push it again and wait. Each time, it stops along the same line, a bit like a dog's tail that always curls back, however many times you straighten it.

The result: a freely suspended magnet always comes to rest along the north-south direction. (If you know where the Sun rises and sets, you know where East and West are, so you can tell which way this line runs.)

The end that points north is called the North-seeking pole, or the North pole of the magnet. The end that points south is the South-seeking pole, or the South pole. A hanging magnet rests this way because the Earth itself behaves like a giant magnet.

Now hang a small iron bar the same way. Does it always rest north-south? No. It can stop facing any direction. Only a magnet rests along the north-south line. So hanging a piece of metal freely by a thread is a way to test whether it is a magnet.