Every magnet has two poles, and that is where the pull is strongest

1. Roll a bar magnet through iron filings and they cling in thick tufts at the two ends and almost nowhere along the middle, which shows the force is concentrated at the poles.
2. Hang the same magnet from a thread so it can swing freely and it always settles with the same end pointing towards the Earth's geographic north.
3. That end is the north-seeking pole, written N pole, and the opposite end is the south-seeking pole, written S pole.
4. Poles always come in pairs, so snapping a bar magnet in half does not give you a lone N pole: you get two shorter magnets, each with its own N pole and S pole.
5. A bar that behaves like this is magnetised, while an identical-looking bar with no poles and no preferred direction is unmagnetised.

Like poles repel, unlike poles attract

1. Bring the N pole of one magnet up to the N pole of a second magnet hanging on a thread and the hanging magnet swings away, which is repulsion.
2. Two S poles do exactly the same, so the rule is that like poles repel.
3. Bring an N pole up to an S pole and the hanging magnet swings towards it, so unlike poles attract.
4. Both are non-contact forces: they act across an air gap, with no need for the magnets to touch.
5. The force grows rapidly as the gap closes, which is why two strong magnets snap together over the last few millimetres.
6. The two magnets always push or pull on each other equally and in opposite directions, so a large magnet does not feel a smaller force than the small one it is pulling.

Repulsion is the only proof that a bar is magnetised

1. An unmagnetised magnetic material, such as an iron nail, is attracted by either pole of a magnet, because the magnet first turns the nail into a magnet and then pulls on it.
2. A magnetised bar is attracted by one pole of a test magnet and repelled by the other.
3. Attraction therefore cannot separate the two cases, because both a magnet and a plain iron nail get pulled in.
4. Repulsion can only happen between two magnets, so a push is decisive evidence.
5. To test an unlabelled steel bar, bring each of its ends near a known N pole in turn: if either end is pushed away, the bar is a magnet.

Magnetic materials are a short list of metals, not metals in general

1. Steel is mostly iron, so anything made of steel is magnetic: paper clips, food tins, screws and the body panels of a car.
2. Non-magnetic materials are not attracted at all and cannot be magnetised, and they include copper, aluminium, brass, gold, plastic, wood, glass and rubber.
3. Copper and aluminium are excellent electrical conductors yet a magnet ignores them completely, so being a metal and being magnetic are separate properties.
4. You can test this with loose change: a magnet picks up a 1p and a 5p because both are steel underneath their plating, but leaves a 20p behind because it is cupronickel.
5. Recycling plants use the same difference: a large magnet lifts the steel cans off the conveyor belt and leaves the aluminium ones behind.