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08/01/1996 07:00:00

Question of the month: Why do magnets stick to other magnets?

Question of the Month Question from: Matthew, age 8 1/2, Pasadena

Answered by: Doug Michael, PhD, Senior Research Fellow in Physics

Magnets stick together because they have a magnetic field around them, and this field both pulls on and pushes away other magnets.

If you've played with magnets like those that stick to your refrigerator, you know that sometimes they stick to each other, but that they also can push each other away, depending on which way the magnets are pointing.

Each magnet has a north pole and a south pole (named after the earth's magnetic north and south poles), and the north end of one magnet will stick to the south end of another magnet. But if two north poles or two south poles are placed near each other, the magnets will push each other away.

But this explanation doesn't really say HOW magnets pull and push on each other. To answer that question, we need to think about what creates a magnetic field.

Magnets like those on your refrigerator, which always have a magnetic field, are called permanent magnets. The secret of permanent magnets lies in the material they're made of, which usually is metal that contains a lot of iron.

All matter is made of atoms, which contain electrons. And electrons act like miniature magnets. This is a basic trait of electrons, which arises from physical laws.

In most materials the tiny magnetic fields of electrons point in all different directions, so they neutralize each other and there is no large magnetic field. But in iron and a few other metals that are used to make permanent magnets, these countless tiny magnets are pointing in roughly the same direction. Each miniature magnetic field adds to and reinforces all the others. The total effect creates a noticeable magnetic field, which will pull and push on other, nearby magnets.

Another way to create a magnetic field is with moving electric charges. Electric charges that are standing still exert constant electric forces on the objects around them. But electric charges that are moving exert changing electric forces on the objects around them. If the changing electric forces are all added up as the charges go by, the result is a magnetic field.

Moving electric charges create a magnetic field no matter how they are moving: in a straight line, a spiral, a circle, or some unusual path. One way to create a fairly strong magnet is by sending electricity through a coil of wire; this is called an electromagnet. Electromagnets are temporary magnets; the magnetic field goes away when the electricity is turned off.