Magnets: why do some things stick to a magnet and others do not?

A magnet is an object that pulls on certain materials without touching them. A bar magnet has two ends called poles: a north pole, often marked N, and a south pole, often marked S. When two magnets are brought close together, the poles follow a simple rule: like poles repel, unlike poles attract. That means two north poles push apart, two south poles push apart, but a north pole and a south pole pull together. This basic rule helps explain how compasses and many machines work. (See Curiosity: Textbook of Science for Grade 6, Chapter 4 (Exploring Magnets).)

A magnet does not attract everything. The common magnetic materials are iron, nickel, cobalt and steel. Steel is magnetic because it is mostly iron. Materials that are not attracted include wood, plastic, copper and aluminium. So a bar magnet will pick up an iron nail or a steel paper clip, but it will not pick up a copper wire, aluminium foil, a plastic ruler or a wooden pencil. Notice that copper and aluminium are metals—yet they are not magnetic metals. This is why a magnet sticks to a steel fridge door but not to a copper pipe. (See Curiosity: Textbook of Science for Grade 6, Chapter 4 (Exploring Magnets).)

Around every magnet is an invisible region called a magnetic field. You cannot see it with your eyes, but you can reveal its shape with iron filings. If you place a thin sheet of paper over a bar magnet and sprinkle iron filings on top, the filings line up in curved patterns from one pole to the other. The pattern is strongest near the poles. A compass is a small magnet that is free to turn. Because Earth itself acts like a giant magnet, the compass needle lines up with Earth's magnetic field. The needle's north-seeking end points toward Earth's magnetic north, which helps people find directions. (See Curiosity: Textbook of Science for Grade 6, Chapter 4 (Exploring Magnets).)

Magnets are used in many everyday devices. Fridge magnets hold notes on a steel door. Electric motors use magnets to spin, and speakers use magnets to make sound. Maglev trains use powerful magnets to float above the track, reducing friction. There is also a deep link between electricity and magnetism: a coil of wire can become an electromagnet when electric current flows through it. The reverse idea—moving magnets can help generate electricity—is explored in Electricity explained: How electricity is generated.