Eli5: How does the compass actually work
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A compass is a small magnet that can rotate along an axis. Most of the time, the strongest magnetic field near it is the Earth’s, so it will align itself so that its south pole is facing the magnetic north pole.
It works because the Earth has a partially liquid iron core, which spins and creates a magnetic field. In effect, this creates an enormous bar magnetic which runs north to south, except the south pole of the Earth’s magnet is (almost) at the geographic north pole.
So, anywhere on Earth is a line of magnetic attraction, and a compass (itself a magnet) is sensitive to this. The north pole of the compass is attracted to the south pole of the Earth (which is at the geographic north pole) and repelled by the Earth’s north pole (which is in Antarctica).
Earth is a magnet, compass needle is also a magnet and magnets attract opposite poles and repel same ones.
The force is small but sufficient to rotate the needle if it’s suspended with very low friction, for example floating on water.
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