Nib asked
Why do magnets repel each other?
Magnets only repel when like poles face each other; unlike poles attract. A magnet's field lines act like stretched rubber bands along their length and push sideways on each other, so two north poles crowd their lines together and shove…
6 steps, drawn by Nib. Read it here, or watch him draw it. Updated .
1the puzzle
A common belief is that magnets repel each other. They do not always. Two magnets attract when a north pole faces a south pole, and repel only when two north poles or two south poles face each other. A bar magnet has a north pole at one end and a south pole at the other, and the two behave oppositely.
Magnets attract unlike poles and repel like poles. Repelling is only half the story.
a common mix-upMagnets do not simply repel each other. Opposite poles attract.
Do two magnets always push each other away?
Show the answer
No. Opposite poles attract, only matching poles repel.
2tiny magnets
Each electron has a tiny magnetic moment, a property tied to its spin. In most materials these point every which way and cancel. In iron, nickel and cobalt, regions called domains line up their moments, and in a permanent magnet most of the domains agree. The tiny fields add up to one big one with a north and a south pole.
A magnet's field is the sum of countless aligned electron magnets.
3unlike: attract
Field lines are a way to draw the direction of a magnetic field. They leave a north pole and arrive at a south pole. When a north pole faces a south pole, the lines run straight across the gap from one magnet to the other, linking them.
With unlike poles, field lines run across the gap and link the magnets.
4like: crowd
When two north poles face each other, field lines leaving one cannot arrive at the other. Each set loops back around to its own magnet's south pole. The lines are squeezed together in the narrow gap between the poles, where the two fields point against each other.
With like poles, the field lines cannot join, so they bunch up in the gap.
5rubber bands
A useful picture treats field lines like stretched rubber bands that also repel their neighbours sideways. Lines joining a north and a south pole try to shorten, which tugs the magnets together. Lines pressed side by side in the gap between two like poles push on each other, and that pressure shoves the magnets apart. The field stores energy, and the magnets move to lower it.
Field lines pull along their length and push sideways, so linked lines attract and crowded lines repel.
6the whole idea
A magnet has two poles, and its field comes from electron spins lined up inside the metal. Unlike poles let the field lines link, and the lines pull the magnets together. Like poles force the lines to bunch up in the gap, and the crowded lines push the magnets apart.
Linked field lines attract; crowded field lines repel.
Magnets only push apart when matching poles meet, because their fields crowd together like pressed rubber bands in the gap.