In physics, magnetism is a force that can attract (pull closer) or repel (push away) objects that have a magnetic material like iron inside them (magnetic objects). In simpler words, it is a property of certain substances which pull closer or repel other objects. Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. Magnetism is one aspect of the combined phenomenon of electromagnetism. Magnetism affects magnetic materials and electric currents. The effect of a permanent magnet on ferromagnetic materials is so strong that a ferromagnetic material can be magnetised to become a permanent magnet - for example, iron, nickel, cobalt etc. The motion of electric charges causes magnetism. Every substance is made up of tiny units called atoms. Each atom has electrons, particles that carry electric charges. In substances such as iron, cobalt, and nickel, most of the electrons spin in the same direction.