Hold a magnet a little way above a steel paperclip on the table. Nothing is touching… and yet the paperclip suddenly jumps up and sticks to the magnet, all by itself. No string, no glue, no wind. What just grabbed it?
A magnet has an invisible pull that reaches out across a gap and tugs on
certain things without ever touching them. We call that a
non-contact force — a push or a pull that works through thin air. Like
Grab a magnet and go round the room touching it to everything you can find. Straight away you notice something odd: the magnet is fussy. It clamps hard onto some things and completely ignores others.
Things a magnet grabs are almost always made of iron or steel (steel is mostly iron): a paperclip, a nail, a fridge door, a tin can, a pair of scissors, a screw. A metal called nickel works too. Things a magnet ignores are everything else — plastic, wood, paper, glass, rubber, your hand.
Here comes the twist that surprises everybody. A magnet does not stick to all metals. An aluminium drinks can, a copper coin, a gold ring, a silver spoon — all shiny metals, and the magnet slides right off every one of them. So "is it metal?" is the wrong question. The right question is: "does it have iron in it?"
Look closely at a bar magnet and you'll see its two ends are marked with letters, often painted in two colours. Those ends are the magnet's poles. One end is the North pole (N) and the other is the South pole (S).
The poles are where the magnet is strongest — dip a bar magnet in a bowl of paperclips and the biggest clumps grab onto the two ends, while the middle stays almost bare. Every magnet has exactly these two poles, a North and a South. Hold that thought — it's about to explain the magnet's most famous trick.
Take two magnets and slowly bring them together end to end. Sometimes they leap together and clamp tight. Turn one of them around and try again, and now they push back, so hard you can feel them squirming to escape each other. The difference is which poles are facing:
A short way to remember it: unlike poles attract, like poles repel. In the box below, flip the facing poles and watch the arrows swap direction. Then close the gap and watch the arrows grow — the nearer the magnets get, the stronger the pull or push.
A magnet doesn't have to touch a paperclip to pull it — so there must be something reaching out around the magnet, filling the space near it. That invisible region of pushing and pulling is called the magnet's magnetic field. It's strongest right at the poles and gets weaker the further out you go, until, far enough away, it fades to nothing.
You can't see a field… but you can make it show itself. Lay a magnet under a sheet of paper and sprinkle tiny iron filings on top. Give the paper a tap and the filings hop into neat curving lines, sweeping from the North pole round to the South. Those lines are a map of the field — bunched up tight and crowded near the poles (strong there), spread out thin in between (weaker there).
Here is the strangest fact about magnets. The whole Earth is one enormous magnet, with a North pole and a South pole of its own, deep in the spinning iron at its centre. That's the secret behind a compass: the needle is just a tiny magnet, free to swing, and the giant Earth-magnet tugs its ends round until it points North–South. Wherever you stand, the needle finds North — which is why explorers, sailors and hikers have trusted it for hundreds of years.
And it isn't only people. Some animals can feel the Earth's magnetism and use it like a built-in compass. Robins steer by it when they fly thousands of miles to a warmer country and back. Sea turtles use it to find the very beach where they hatched, and honeybees and even some bacteria line themselves up with it. A magnetic sense we can't feel at all is, for them, an everyday map.
Once you know the tricks, you start spotting magnets all over the house and the world:
Not bad for an invisible force you can hold in your hand.
Remember that same poles repel? Engineers turned that push into a train. A maglev (short for "magnetic levitation") train carries powerful magnets, and the track carries magnets too, arranged so they push against each other. The whole train is shoved gently upwards and floats a few centimetres above the rail, touching nothing at all. With no wheels rubbing on the track, it can glide along faster than a racing car — the quickest maglev trains whoosh past at over 600 kilometres an hour.
The very strongest magnets ever built are stronger still — powerful enough to lift a real car clean off the ground, or, in a science lab, to make a live frog gently float in mid-air. Magnetism, it turns out, is not a small force at all.