Magnets can be big or small, strong or weak and permanent or temporary.
Permanent magnets always have a magnetic field so they can always attract metals with their magnetic power. The horseshoe magnet, with its two poles side by side and the bar magnet, with its two poles on opposite ends, are both permanent magnets.
Temporary magnets can be turned on and off. The electromagnet is a temporary magnet made by combining electricity with metal to create a magnetic field. This magnetic field can be switched on and off, making it ideal for machinery that doesn’t need to run all the time.
Magnets can be soft or hard.
Materials like iron are good temporary magnets when you put a magnet near them, but they lose some or all of their magnetism when you take the magnet away. These materials are called magnetically soft.
Mixes of iron and rare-Earth metals (nickel and cobalt) are good permanent magnets. They keep most of their magnetism even when you remove them from a magnetic field. These materials are called magnetically hard.
If a magnet is strong enough it can pull through gases, solids and even liquids. The area around the magnet that attracts or repels another object is called the magnetic field. Objects must be inside the magnetic field to respond to the magnet. This is why a small magnet doesn’t always attract things that are far away. The closer you get to the magnet the stronger the force.
Scientists measure magnetic fields with an instrument called a magnetometer. This instrument can also be used to measure the magnetism in rocks. Believe it or not, some rocks also have magnetism! These rocks become magnetised by the Earth’s field while they are still being formed.
Not all materials are magnetic. Some materials like iron stick to magnets easily and others like plastic and glass do not.
Ferromagnetic materials are strongly attracted to magnets. Their structure lets magnetic fields pass through them easily. Examples are iron, cobalt and nickel.
Paramagnetic materials have a very weak attraction to magnets which is hardly noticed at all. Examples are aluminium, zinc and sodium.
Diamagnetic materials are not attracted to magnets, they repel them. Examples are water, copper and gold.