How Magnets Pull: Poles, Materials, and Fields

Magnets are not magic, but they do follow rules. In Curiosity: Textbook of Science for Grade 6, Chapter 4 (Exploring Magnets), magnets are described by what they do: they attract some objects, they repel other magnets, and they always have two ends that behave differently. These ends are called poles. One end is the north-seeking pole, often called the north pole, and the other is the south-seeking pole, often called the south pole. A bar magnet usually has its poles at the two ends. If you hang a bar magnet freely, one end turns toward the north and the other toward the south.

A strange and useful rule about poles is that they never come alone. If you cut a bar magnet into two pieces, you do not get one north-only piece and one south-only piece. Instead, each piece becomes a complete smaller magnet with its own north pole and south pole. You can cut the pieces again and again, and the same thing happens. This is why a broken magnet still works: the two new ends become opposite poles.

Magnets follow a simple rule: like poles repel, and unlike poles attract. Bring two north poles together, and they push apart. Bring a north pole and a south pole together, and they pull together. You can test this with two bar magnets. If an unknown pole is attracted to a known north pole, the unknown pole must be a south pole. If it is repelled, it must be a north pole. This is a reliable test because attraction alone can be misleading with magnetic materials, but repulsion only happens between like poles.

Why do iron, nickel, cobalt, and steel get attracted while wood, plastic, copper, and aluminium do not? A simple model can help. Think of a magnetic material like iron as being made of many tiny regions called domains. Each domain acts like a tiny magnet. Normally the domains point in all directions, so their pushes and pulls cancel out. When a magnet comes close, many domains line up in the same direction. The iron then behaves like a temporary magnet and is pulled toward the magnet. In wood, plastic, copper, and aluminium, there are no tiny magnetic domains that can line up this way, so they do not get attracted. This domain picture is a model—a useful way to imagine something too small to see.

Some magnets are permanent and some are temporary. A permanent magnet, such as a bar magnet or a fridge magnet, keeps its magnetism for a long time. A temporary magnet acts like a magnet only when it is near a strong magnet or when it is made in a simple way. You can magnetise a steel needle by stroking it many times in one direction with one pole of a permanent magnet. Lift the magnet away at the end of each stroke, and repeat. The needle becomes a temporary magnet. If you test it with iron pins, it can pick up a few. It will slowly lose much of its magnetism, especially if it is dropped or heated.

A magnet does not need to touch an iron nail to pull it. Around every magnet there is an invisible region of influence called the magnetic field. The field is strongest near the poles. You can make the field visible by placing a sheet of paper over a bar magnet and sprinkling iron filings on the paper. The filings line up along curved paths from one pole to the other. These patterns show the field's shape, but the field itself is not made of lines; the lines are just a map.