Earth's magnetic field induces some degree of magnetism in most of the iron objects around us. With a compass, you can see that cans of food on your pantry shelf have north and south poles. When you pass the compass from their bottoms to their tops, you can easily identify their poles. Mark the poles, either N or S. Then turn the cans upside down and note the number of days it takes for the poles to reverse themselves. Explain to your friends why the poles reverse.