Lesson 1/Learning Event 1
Magnetism is an invisible force that attracts iron and steel. It was first noticed in a particular type
of stone called magnetite that is a natural magnet. Magnetite was first used as a compass to tell
directions for sailors on the ocean or travelers in unfamiliar country. This was possible because, if
a piece of magnetite is suspended so it is free to rotate, it will turn so it points to the earth's
magnetic north and south poles. One end always points to the north so this is called the north pole
and the opposite end is called the south pole.
Pieces of magnetite, natural magnets taken from the earth, have little value now. Better magnets
can be made from iron and steel by artificial means. Magnets that are made from soft iron are
known as "temporary" magnets because they lose their magnetism quickly. Magnets made from
steel are known as "permanent" magnets because they stay magnetized for a long time. Permanent
magnets that most of us are familiar with are the bar- and horseshoe-shaped kinds. Let's discuss a
few experiments with some permanent bar magnets to gain some knowledge of the invisible forces
they possess.
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If a bar magnet is suspended by a thread, it will swing into a north-south direction with its
ends pointing to the earth's magnetic poles. Like the magnetite, the end of the magnet
toward the north is known as the north pole and the end to the south the south pole.
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If we obtain a second bar magnet and move its north pole toward the north pole of the
suspended magnet we can see that the suspended magnet moves away from the second
magnet. Likewise, if the south poles are moved close together, the suspended magnet will
move away. Therefore magnetic poles that are alike repel each other.
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Now, let's move the south pole of the second bar magnet toward the north pole of the
suspended magnet. Instead of moving away as it did before, the suspended magnet now
moves toward the second magnet. In fact, if we allow the north and south poles of the
magnets to come in contact, they stick together, and it takes considerable force to pull
them apart. This last experiment then proves that unlike magnetic poles attract each
other.
The surrounding space around a magnet that is affected by the magnet's invisible force is known as
a MAGNETIC FIELD. The magnetic field is often demonstrated by sprinkling some iron filings
on a piece of paper that has been placed on a tabletop. A bar magnet is then dropped into the
center of the paper. Of course, a large number of the filings are immediately attracted and moved
about by the magnet.
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