Permanent magnets can be made in a variety of shapes ranging from rectangular bars to disks, rings or horseshoes.
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In ancient Greek and Roman times, there is mention made of mysterious stones which could not only attract one another, but also small pieces of iron. These stones were known as "lodestones" and they contained magnetite, which is a naturally occurring magnet. Strong permanent magnets are a relatively recent invention dating back to the 1940s.
Magnets are formed by being cast in a mould and then ground to reach desired dimensions, or they may begin in a powdered form which is then pressure bonded. The four types of common magnets in use are Alnico, Neodymium Iron Boron, Ferrite and Samarium Cobalt.
The strength of a magnet is determined by its size and shape. A big magnet is stronger than a small magnet made from the same material. A bar magnet is not ideally shaped to provide much lifting power. The reason for shaping a magnet like a horseshoe, or a "U," is because it is then able to provide greater lifting power.
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