33. Earth's magnetic field induces some degree of magnet- ism 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 bot- toms 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 them- selves. Explain to your friends why the poles reverse