Magnetism is a physical phenomenon that occurs when certain materials, such as iron, steel, nickel, and cobalt, are exposed to an external magnetic field. It is a force of attraction or repulsion between objects that have a magnetic field. The strength of the magnetism depends on the material and the strength of the magnetic field. Magnetism can be used to generate electricity or to store information on computers. It can also be used to create navigation systems and to manipulate objects in space.