In this section, you will learn: Magnetism Learning outcomes In this section, you will learn: That magnetism is a force. That a magnet can exert a force of attraction or repulsion. That the space around a magnet is called a magnetic field. That the earth is a giant magnet. What a compass is and what the connection is with magnetism. 1

The force of magnetism Since magnetic materials can cause other materials to move from rest, magnetism is a force. Magnets will exert a force on iron, nickel, cobalt and some alloys (mixtures of metals), but other materials like paper, wood and plastic are not affected by magnets. 2

Magnetic forces Unlike gravity, which is a force of attraction only between bodies, magnetism can attract or repel. We think of magnets as having two poles, North and South. The two poles have different effects on each other. Like poles repel each other, unlike poles attract each other. 3

The magnetic field Since certain metals will experience a force in the space around a magnet, we say that there is a magnetic field around a magnet. A magnetic field is the region of space around a magnet in which certain materials will experience a magnetic force. 4

Picturing magnetic fields You can picture the magnetic field around a magnet by drawing lines, called field lines, from the North to the South poles of magnets. 5

The magnetic field of the earth The earth is a giant magnet. It causes forces as if there were a huge bar magnet at its centre. You can demonstrate the earth’s magnetic field by hanging a magnet from a thread. It will always line up in the same direction. The magnetic pole over the Arctic is not in the same place as the geographical pole. The magnetic pole moves around the geographic pole. 6

The magnetic compass A compass is a small magnet or magnetised needle that is free to move in a protective case. Because the needle is a magnet, it will point towards the pole of the earth’s magnetic field. This is useful in navigation. 7

Summary: Key points Magnetism is a force. Magnets exert a force on certain kinds of metals. The magnetic force can be attractive or repulsive. It is different from the force of gravity in this regard. A magnet is said to have two poles, North and South. Like poles repel each other and unlike poles attract. 8

Summary (continued) The space around a magnet where a magnetic force is experienced is called a magnetic field. Magnetic fields can be illustrated by field lines going from North to South poles. The earth is a giant magnet with a magnetic field. A compass is a magnetised needle that always points to the magnetic pole of the earth. It is used in navigation. 9