BOX 3.1 Playing with magnets

Take two bar magnets. Suspend one from a thread so that it remains horizontal. When it comes to rest, the magnet will line up in a north-south direction. Mark the end of the magnet that points north. Repeat this procedure for the other magnet. While one of the magnets is suspended, bring the other magnet nearby. What happens? If you bring the north poles of the two magnets close, they repel each other. What happens when you bring the south pole of one magnet close to the north pole of the other magnet? They attract. These bar magnets always have a pair of poles. Each piece of the broken magnet has its own north and south poles. Physicists have tried for years to "break" the magnet into separate poles (monopoles), but no one has succeeded (if someone did, he or she would certainly get a Nobel prize!).

The Earth's magnetic field

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