Did you know that the Earth acts like a giant magnet? It causes other magnets to point to the top of the Earth, called the north. You can do experiments that prove this, using a bar magnet. It will always come to rest pointing in the same way, time after time.
Make a free-floating magnet compass by taking a small plastic bowl (or lid), adhesive tape, a bar magnet and a bowl of water. Make sure the North end of the magnet points towards the "N" on your compass.
No matter how often you move the small bowl/lid, it will always stop with the magnet pointing the same way.
The Earth's magnetic force causes the magnet to stop with one end pointing to the top of the Earth (the North Pole) and the other end pointing to the bottom (the South Pole).
Source: The Usborne Big Book of Science Experiments