b. Attraction and Repulsion of Magnetic Poles. Like magnetic poles repel
each other; unlike magnetic poles attract each other. When two magnets are brought
close together so that the north pole of one magnet is directly opposite the north pole of
the other magnet, a repelling force tends to keep the two magnets apart (figure 2-5A). If
the magnets are positioned so that the north pole of one magnet faces the south pole of
the other, a force of attraction pulls the two magnets together (figure 2-5B). The force
(attraction or repulsion) between two magnetic poles is directly proportional to the
product of the strength of the poles and inversely proportional to the square of the
distance between them.
Figure 2-5. Attraction and repulsion of magnetic poles--
like poles repel; unlike poles attract.
2-11. MAGNETIC AND NONMAGNETIC SUBSTANCES
All matter is affected, to some extent, by a magnetic field. Substances that are
strongly attracted by a magnet are called magnetic substances. Most materials,
however, are not noticeably affected by magnets; they are classified as nonmagnetic
a. Magnetic Materials. Iron and steel are strongly magnetic. Cobalt, nickel,
and manganese are also magnetic, but to a lesser degree. These substances, or their
alloys, are used to make permanent magnets.
b. Nonmagnetic Materials. Most common materials, such as wood, copper,
glass, brass, lead, tin, silver, gold, rubber and plastics are nonmagnetic and, therefore,
cannot be magnetized.