21.1  Magnets and Magnetic Fields (continued)

Magnetic Forces

You can explore properties of magnets on your own. Either side of a magnet sticks to a refrigerator. Yet if you push two magnets together, they may attract or repel. Magnetic force is the force a magnet exerts on another magnet, on iron or a similar metal, or on moving charges. Recall that magnetic force is one aspect of electromagnetic force.

Magnetic forces, like electric forces, act over a distance. Look at the suspended magnets in Figure 1. If you push down on the top two magnets, you can feel the magnets repel. Push harder, and the force increases. Magnetic force, like electric force, varies with distance.

Gilbert used a compass to map forces around a magnetite sphere. He discovered that the force is strongest at the poles. All magnets have two magnetic poles, regions where the magnet's force is strongest. One end of a magnet is its north pole; the other end is its south pole. The direction of magnetic force between two magnets depends on how the poles face.   Like magnetic poles repel one another, and opposite magnetic poles attract one another.

Figure 1  The green magnet and lower red magnet attract each other. The lower red magnet and the yellow magnet repel each other.