Magnets come in many different shapes and sizes. These shapes reflect the individual strength of each magnet. The strength determines function.
Bar magnets are some of the weakest types of magnets and come in the shapes of bars. The size of the magnet also effects it's strength, but in comparison to other magnets of equal size, they have the least amount of magnetism. Bar magnets are used for everyday functions such as hanging things on a refrigerator or for closing cabinets. These magnets are the cheapest and easiest magnets to replace.
Horseshoe magnets were originally made to compensate for the very weak strength of bar magnets. By making both ends of the magnet point in the same direction, the strength of the magnet basically doubles. These magnets are primarily used for picking up paper clips or hard-to-reach small pieces of metal in construction or engineering. They are also widely used in science experiments and classes, as they are a simple magnetic tool to use.
Magnets that are a helical coil of wire are called electromagnets, and they are some of the strongest magnets that exist. However, they only become magnetic when there is electrical current flowing through a wire into the magnet itself. The strength and polarity of the magnetic field created by the electromagnet is adjustable based on the current running through the wire. Electromagnets are used in moving parts such as CD players, DVD players, automatic windows, hard drives and automatic doors in supermarkets.