^BMagnetism.^b Iron filings attracted to the North (N) and South (S) poles of a horseshoe magnet. The magnet induces magnetism in each of the filings, which are then attracted to the magnet and to each other. Although the magnetic field is actually continuous, interactions between the filings cause them to accumulate along arching lines, such as the arc formed at lower centre. Magnetism, one of the basic forces, is caused by the alignment of electrons within a material. Iron is a common material that can be magnetized.