How Magnets Behave

Each magnet has two poles, at which the attractive force seems greatest. The poles are called north-seeking, or north (N), and south-seeking, or south (S). (The poles are so named because, under the influence of the earth's magnetism, a bar-shaped magnet free to rotate will turn so that one pole points northward and the other southward.) When a magnet is cut into two or more pieces, each piece becomes a new magnet.

Like poles repel; unlike poles attract. When the N poles of two magnets are brought together, the magnets will be repelled—that is, they will move away from each other. The same thing happens when the S poles are brought together. When the N pole of one magnet is brought near the S pole of another, however, the two magnets will strongly attract each other, and will move toward each other.

Magnets do not have to come into contact to repel or attract each other because magnetism acts at a distance. The area in which the effect of a magnet can be detected is called its magnetic field. The field is strongest near the magnet; it weakens as the distance from the magnet increases. A magnetic field is usually pictured as a series of lines, called lines of force, extending from the N pole of a magnet to an S pole, either at the other end of the same magnet or in a nearby magnet.

Magnets attract objects made from iron, steel, cobalt, or certain other materials. In the presence of a magnet, an object made from such magnetic materials will itself become a magnet. (This process is called magnetic induction.) The magnet attracts the object because the pole of the magnet closest to the object produces an unlike pole in the nearest part of the object. For example, the N pole of the magnet will produce an S pole in the part of the object closest to it. (In this example, the most distant part of the object would become an N pole.)

Measurements with extremely accurate instruments show that all materials have some reaction to a magnetic field. The materials usually referred to as nonmagnetic, such as copper and water, are either paramagnetic (showing a slight tendency to line up parallel to the lines of force of a field) or diamagnetic (showing a slight tendency to line up at right angles to the lines of force). Magnetic materials, properly called ferromagnetic, have a strong tendency to line up parallel to the lines of force.