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EMM Lesson 5 MAGNETIC FORCES Notes• Magnetism is one of the most interesting mysteries of the natural world. • It can A. Levitate objects B. Act through solid object including human hands C. Pull on things without touching them 2 Notes • Magnetism makes A. Electric motors spin B. Loudspeakers and earphones work C. Refrigerator doors stay closed D. Televisions, video records and household electricity (produced by electric generators) possible. 3 Notes • Permanent magnets all share a common characteristic: they must contain either iron, nickel, cobalt or a combination of these elements. • The exert forces on other magnets and can attract other materials that become magnetized in the presence of a permanent magnet. 4 Notes• Permanent mangets have a north and a south pole. • The north pole of a magnet is attracted to the magnetic pole in the northern hemisphere of the earth. • A suspended magnet will align itself so that its north pole points to “magnetic north”. • Loadstone is a natural permanent magnet. 5 Notes• When two magnets are placed near each other, a force of interaction is exerted between them. • Like poles (north-north or south-south) will repel one another. • Opposite poles (north-south) will attract one another. “Opposites attract, likes repel”. 6 Notes• The force of interaction depends on the distance between the magnets. • The closer two poles are placed to one another, the stronger the force of interaction, and this decreases as they are moved further apart. 7 Notes• The space around a magnet is called a “magnetic field” because it can influence objects without touching them. • The field is the region around the magnet in which magnetic forces will act on objects. 8 Notes• Some objects are not naturally magnetic but become magnetic in the presence of a magnetic field. These materials are called paramagnetic. • Example: Paper clip • Not all metals are attracted to a magnet. • Ex: aluminum foil 9 Notes• Why are only certain metals attracted to a magnet? • Why are some seemingly nonmetallic objects also attracted? 10 Notes• Flexible magnets are made of rubber and plastic and may contain tiny particles of iron or ferrite. Ex. Audiotape and videotape • On flexible magnets, one flat side is the north pole and the other is the south pole. • If you put two flexible magnets together with the north pole stuck to the south pole, it will create a single, stronger magnet 11 Vocabulary • attraction • compass • constant • magnet • magnetism • magnetic pole • repulsion 12