A magnet attracts other magnets, and it also attracts some iron and steel things, such as pins and paper clips. A magnetic field is the area around a magnet where its force can be felt, and every magnet has a north pole and a south pole. Opposite poles attract each other, and the same poles push each other away. Two kinds of magnets exist, permanent magnets and temporary magnets, and in a permanent magnet the tiny magnetic regions called domains line up in the same direction. If you heat up a permanent magnet, the net magnetism goes away, and there is one rule worth keeping, which is that magnets are not for mouths or small children. Loose magnets can hurt children if they are swallowed. If a child swallows more than one, the magnets can pull together inside the body and cause serious damage.

An electric current creates a magnetic field. Magnetism is caused by the motion of electric charges, and in 1820 Hans Christian Ørsted's discovery showed that electricity and magnetism are related. François Arago found that unmagnetized iron filings orient themselves in a circle around a copper wire carrying current. Iron filings around a current-carrying wire disperse when the current is stopped. Parallel wires carrying current in the same direction attract each other. Joseph Henry introduced the electromagnet, and William Sturgeon built the first practical electromagnet, strong enough to support 20 times its own weight. Electromagnets are not permanent, but they can be far stronger than the strongest permanent magnet.

Strong magnets do a lot of work. Very strong rare-earth magnets have been made from alloys of samarium or neodymium with cobalt. Superconducting wires can be wound into coils to create powerful magnets. The MagLab's most powerful non-destructive magnet generates a field of 100 tesla, as of November 2026. In a Maglev train, superconducting magnets suspend the train car above a U-shaped concrete guideway. The magnets in a Maglev train repel one another when matching poles face each other, just as ordinary magnets do. In a Maglev system the powered guideway drives the train.

Earth is a magnet, and its magnetic field begins in its core. The motion of electrically conducting iron in Earth's outer core makes electric currents, and those currents generate the field. Invisible lines of force flow between Earth's magnetic poles, which are not the same as the geographic North and South Poles. Earth is surrounded by a large magnetic shield called a magnetosphere, and it protects us from harmful charged particles in space. The Sun sends out a flow of charged particles called the solar wind. The solar wind creates temporary cracks in Earth's magnetic shield, letting some energy reach Earth's surface daily. Since these solar-wind intrusions are brief, they do not cause significant issues.

How do people follow the field? A magnetic compass has a magnetized needle that turns to line up with Earth's magnetic field. People have used compasses for hundreds of years to find their way, and a lodestone compass was used in navigation as early as 1086. Magnetic declination is the angle between magnetic north and true north. Declination is positive when the angle measured is east of true north and negative when west. Magnetic declination is unreliable near the poles, and at the magnetic poles a compass does not show direction. Edmond Halley carried out the first magnetic declination survey. Earth's magnetic north pole is moving, and this gradual shift must be regularly accounted for in navigation, as of November 2026.

During a pole reversal, Earth's magnetic north and south poles swap locations. The magnetic field weakens but does not completely disappear. During a reversal the magnetic field becomes jumbled, and multiple magnetic poles can emerge in unexpected places. The last time Earth's magnetic field reversed was about 750,000 to 780,000 years ago. Consecutive reversals have been spaced from 5 thousand years to 50 million years apart. Even if Earth's magnetic field were beginning a reversal, it would take several thousand years to complete. Direct observations of Earth's magnetic field extend back just a few centuries, so scientists rely on indirect evidence. Plant and animal fossils from the period of the last major pole reversal do not show any big changes. Scientists have no reason to believe an Earth magnetic pole flip is imminent, as of November 2026.

Words to know

• filings: tiny iron bits
• declination: compass angle
• reversal: a swap
• electromagnet: magnet from current