Every magnet has north and south magnetic poles. Like electric charges, opposite poles attract and like poles repel. Unlike electric charges, poles always come in pairs.

Every magnet has a magnet field responsible for the force it exerts on other magnetic objects. This field is represented by magnetic field lines drawn form the north to south poles.

Most magnetic materials are divided into domains with different magnetic fields. When an external magnetic field is applied, the fields of the domains align along the direction of the external field.

The earth itself has a magnetic field. Its magnetic poles do not coincide with the geographic poles we are familiar with.

The Aurora Borealis is caused by electrons from space that get trapped in the magnetic field of the Earth.

There is a connection between electric current and magnetic fields. When current flows through a straight wire, a magnetic field circles the wire. When current flows through a wire loop, the magnetic field is a straight line though the center of the circle.

The magnetic field produced by a cylinder of wire coils is exactly the same as that produced by a bar magnet.

This property is used to create electromagnets with electricity. When current flows through the wire around the nail, a magnetic field is induced in the nail and it becomes magnetic.

An orbiting electron in an atom is a form of electric current, and so it creates a magnetic field. If the total field from all the electrons is not zero, the material is paramagnetic.

Liquid oxygen is suspended between two magnetic poles. Oxygen is an example of a paramagnetic material.

If the total field in the atom is zero, an external field can induce a weak internal field. Such materials are called diamagnetic. Frogs, grapes, or even people -- anything with water in it -- are diamagnetic!

When some materials are cooled below a critical temperature, they become perfect conductors, called superconductors. Then the magnetic field inside them vanishes, regardless of any external field.

A superconductor (the black slab) exerts a repulsive force on a magnet (the metallic cylinder), supporting the magnet in midair.

Magnetic trains use electromagnets to hover above the track and move at very high speeds with almost no friction.

Electromagnets are also used to store information by encoding it on magnetic tape. When a certain magnetic field is applied to the tape, the magnetic material on the tape lines up with the field.