Magnetic forces

Cutting a magnet in half creates two magnetsA basic property of magnets is that they contain two magnetic poles of opposite polarity, referred to as the magnetic north pole and magnetic south pole. All magnets must have both a north and a south pole. If you cut a permanent magnet in half, each of the halves will have a north and a south pole! This is a fundamental difference between magnetism and electrostatics: You can separate positive charges from negative charges, but you cannot separate a magnetic north pole from its magnetic south pole. You will learn more about electric charges in section 2 of this chapter. Read the text aloud
Magnetic attraction and repulsionWhen two magnets are close to each other they exert attractive or repulsive magnetic force on each other depending on how their poles are aligned. When opposite magnetic poles—north and south—face each other, the magnetic force is attractive. When similar magnetic poles face each other, north–north or south–south, the magnetic force is repulsive. Read the text aloud
Have you ever handled two very strong magnets that, when you joined them together, were stuck so strongly that you could barely separate them? Why do magnets that are so close together stick together so strongly? The answer is that the force between two magnets falls off more rapidly than an inverse-square-law relationship. This also means that the force at shorter distances increases more rapidly than an inverse-square-law relationship. So the forces become extremely strong at short distances, resulting in magnets that are stuck together and very hard to separate from each other! Read the text aloud Show Scaling laws for the force between two magnets
Torque caused by magnetic forceBecause magnets are dipoles the strength of the magnetic force decreases very quickly as they are separated. Think about the attraction between the north pole of one magnet and the south pole of a second magnet. The south pole of the first magnet is repelled by the south pole of the second magnet. The force between two magnets is an example of a dipole–dipole interaction because it includes four poles: two north and two south. Opposite magnetic forces on the two ends of a bar magnet can create a torque that causes the magnet to twist or rotate. Later in the chapter, we will see how magnetic torque can be used in a simple electric motor. Read the text aloud
How small do you have to cut a magnet before you can find a single north pole or a single south pole? Show

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