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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
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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.
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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.
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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.
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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”.
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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.
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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.
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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
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Notes• Why are only certain metals attracted to a magnet?
• Why are some seemingly nonmetallic objects also
attracted?
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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
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Vocabulary
• attraction
• compass
• constant
• magnet
• magnetism
• magnetic pole
• repulsion
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