A magnetic field is the invisible area of force around a magnet! You cannot see a magnetic field, but you can observe its effects when a magnet pulls a paperclip or when iron filings align along the field lines. The magnetic field is strongest at the poles (ends) of the magnet and weaker farther away. Earth itself has a magnetic field (the magnetosphere) that protects us from solar wind and helps compasses point north. Magnetic fields are also produced by electric currents. Every magnet has a north pole and a south pole.

Like poles repel! The rule is: opposite poles attract, like poles repel. This is because the magnetic field lines flow from the north pole to the south pole outside the magnet. When two north poles are brought together, their magnetic field lines push against each other, causing repulsion. When a north pole and a south pole are brought together, the field lines connect, causing attraction. This rule applies to all magnets, whether they are bar magnets, horseshoe magnets, or electromagnets. The same principle also applies to electric charges (opposites attract, like charges repel).

Iron is magnetic! Iron is one of the three naturally magnetic metals (iron, nickel, cobalt). Many everyday objects contain iron and are attracted to magnets: paperclips, nails, some screws, refrigerator doors (the outer surface is usually stainless steel, which may not be magnetic, but the inner door is often magnetic). Magnetic metals are called ferromagnetic (from the Latin word for iron, "ferrum"). Some alloys (mixtures of metals) are also magnetic, such as steel (iron + carbon) and alnico (aluminum, nickel, cobalt). If a magnet does not stick to a metal, that metal is non-magnetic (like aluminum foil, copper pipes, or gold jewelry).

A compass points toward magnetic north! The north pole of the compass needle is attracted to Earth's magnetic south pole (located near the geographic North Pole). There is a difference between geographic north (the North Pole, where the Earth's axis is) and magnetic north (the point where compasses point). Magnetic north moves over time (about 40 km per year). The Earth's magnetic field has reversed many times in the past (magnetic north becomes magnetic south). The last reversal was about 780,000 years ago. The magnetic field is generated by the "dynamo effect" – the motion of molten iron in the outer core. Without this magnetic field, Earth would be bombarded by solar wind, and life might not exist.

A temporary magnet becomes magnetic only when near a permanent magnet! Temporary magnets are made of "soft" magnetic materials (like iron or steel) that can be magnetized easily but also lose their magnetism easily. Permanent magnets are made of "hard" magnetic materials (like alnico or neodymium) that retain their magnetism. Electromagnets are temporary magnets powered by electricity. When you turn off the electricity, the electromagnet loses its magnetism. Electromagnets are used in electric motors, generators, cranes (to lift scrap metal), and MRI machines. Refrigerator magnets are permanent magnets. The difference between temporary and permanent magnets is important for many technologies.

The electric current controls the magnetic force! Increasing the current (more electricity) increases the magnetic force. Adding more coils of wire also increases the strength. Using an iron core (instead of air) greatly increases strength. Electromagnets are incredibly useful because they can be switched on and off. For example, a crane uses an electromagnet to lift scrap metal – when the current is on, the magnet picks up the metal; when the current is off, the metal drops. Electric motors use electromagnets to create motion (a rotating magnetic field). Speakers use electromagnets to vibrate the cone and produce sound. Without electromagnets, modern technology would not exist. The first electromagnet was invented by William Sturgeon in 1825.

All of these use magnets! Speakers contain an electromagnet and a permanent magnet that work together to create sound. The electromagnet vibrates back and forth, pushing air and creating sound waves. Compasses contain a tiny magnet that aligns with Earth's magnetic field. Credit cards have a magnetic stripe containing your account information (though many cards now use chips). Electric motors (found in fans, washing machines, cars, and electric toothbrushes) use electromagnets to create rotation. Hard drives use magnets to read and write data. MRI machines use powerful electromagnets to image the inside of the human body. Without magnets, our world would be very different!

Ørsted and Faraday made key discoveries! In 1820, Danish scientist Hans Christian Ørsted noticed that a compass needle moved when he turned on an electric current nearby – proving electricity creates magnetism. In 1831, English scientist Michael Faraday discovered that moving a magnet near a coil of wire creates an electric current – this is how generators produce electricity. These discoveries led to the theory of electromagnetism, unified by James Clerk Maxwell in the 1860s. Electromagnetism is one of the four fundamental forces of nature (along with gravity, strong nuclear force, and weak nuclear force). Every electric motor and generator works on these principles. Without this understanding, we would not have electricity as we know it.

Magnetic repulsion allows maglev trains to float! Like poles repel (north-north or south-south). By placing powerful electromagnets on the train and track with like poles facing each other, the train can be lifted off the track, eliminating friction. Without friction, maglev trains can reach very high speeds. The first commercial maglev train opened in Shanghai, China (2004), reaching speeds of 268 mph (431 km/h). Japan has a maglev train that reached 375 mph (603 km/h) in a test run. Maglev trains are quieter and require less maintenance than conventional trains. The same principle allows you to float a small magnet above a superconducting material (the Meissner effect). Magnetic levitation is also used in magnetic bearings (for high-speed turbines).

Neodymium magnets are the strongest! A neodymium magnet the size of a coin can lift several pounds. They are called "rare earth" magnets because neodymium is a rare earth element. However, "rare earth" is a misnomer – neodymium is actually fairly common, but it is difficult to extract. Neodymium magnets were invented in the 1980s. They are much stronger than traditional magnets (ferrite or alnico). They are used in hard drives (to read/write data), headphones and speakers (for clearer sound), electric cars (motors), and wind turbines. Neodymium magnets are brittle and can chip or shatter if they snap together. They can also lose their magnetism if heated above 80°C (176°F). Some neodymium magnets are coated with nickel to prevent corrosion. The strongest magnetic field ever created by a permanent magnet is about 10 Tesla (a typical refrigerator magnet is about 0.01 Tesla).