A permanent magnet does not use up magnetism like a battery uses stored chemical energy. Its magnetic field comes from the organised magnetic behaviour of particles inside the material. However, a magnet can become weaker if its magnetic domains become less well aligned. Strong heating, repeated impacts or a powerful opposing magnetic field can cause this. Some magnetic materials hold their domain alignment much better than others, which is why they are chosen for permanent magnets. So magnets do not normally 'run out', but their magnetisation can be reduced by changing the internal arrangement that creates the field.

The useful part of this physics is that it helps people predict and design real things. Engineers often begin with the same simplified model used in school, test where it works, then add more detail when measurements show that the real situation is more complicated.

Magnetism comes from magnetic fields, which exert forces without objects needing to touch. In magnetic materials, many tiny magnetic regions can become aligned, producing a larger overall field. Electric current also produces a magnetic field, which is why coils of wire can act as electromagnets and why magnetic effects can be controlled in motors, speakers, relays and sensors.