Magnets

These two objects are pulled towards each other. If we turn one of the objects, and move it towards the other it is pushed away instead. These are two magnets. They are magnetic. Often we paint magnets, so that one end is red, and one end is white.

A white end and a red end attract each other. But if we turn the red ends toward each other, they repel each other. If we turn white end to white end, they also want to repel each other. This is because a magnet has two poles. We call them the south pole, and the north pole.

And opposite poles attract. While similar poles repel. But how can an object affect another without touching it? What’s there, that can’t be seen, that makes a south pole and a north pole attract each other? To answer that, we start by looking at a compass.

A compass is also a magnet, with a south pole and a north pole. Let’s move the compass around a magnet. The compass turns, and points in different directions, depending on where it is. Let’s mark the direction for every position. This creates a pattern.

From the pattern, we can draw lines. The lines show what a magnetic field looks like around the magnet. The lines are field lines. The magnetic field is what makes the objects affect each other. The field lines run through the magnet, and form arches around it.

The closer the field lines are to each other, the stronger the magnetic field. A magnetic field is invisible, but it is there, and we can see it, with the help of a compass. The compass orients along the magnetic field lines. There’s another common way of showing the field lines. Let’s place a glass-plate above the magnet.

Then carefully pour tiny pieces of iron onto the glass. The iron pieces position themselves along the magnetic field lines. Here are two larger pieces of iron. They neither attract, nor repel. They are not magnetic.

But if a piece of iron approaches a magnet, the iron itself becomes a magnet. And since its south pole is turned to the first magnet’s north pole, they attract. They are pulled together and now the field lines have changed. The first magnet and the piece of iron combined, have become one single, larger, magnetic object. The red and white magnet, that previously had a south and a north pole, is now only a south pole.

And the iron, that previously was not magnetic, has become a north pole. Let’s remove the iron. The original magnet remains. Now let’s try to do the same thing with a piece of aluminium. Nothing happens.

The aluminium does not become magnetic. It’s not attracted. Not repelled. So, different materials can have different magnetic characteristics. Some materials, like iron, can become magnetic.

Others, like aluminium, can not. What happens if we cut the magnet in half, so that the south pole is separated from the north pole? Then we have two smaller magnets, each with a south pole and a north pole. The earth, has masses of iron in its core. And around the earth, there are magnetic field lines, with one magnetic north pole and one magnetic south pole.

The earth is a magnet. A huge one. And remember how compasses behave? They orient along magnetic field lines. And since the magnetic poles of the earth are close to its geographical poles The compass points almost directly north, and almost directly south.

So thanks to magnetism a compass can always show us where north and south are.