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GRADES K - 8
MAGNETS
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GRADES K - 8
MAGNETS
BACKGROUND INFORMATION:
What is a magnet? A magnet is a body
which attracts iron, combinations of metals
(known as alloys) or other materials which
are composed of iron or iron-like substances. "Attract" means an
object composed of iron will attach or affix
itself to the magnet. Additionally, the magnet
can "magnetize" other objects which in turn
act like magnets. Other iron objects
will be attracted to the magnetized object.
The two ends of the magnet are different and
are referred to as the north and south pole
(or north-seeking pole and south-seeking pole).
Like poles repel. The south poles of two
magnets will not attract one another. Neither
will the north poles of two magnets. The north
pole of one magnet and the south pole of
another magnet will attract one another.
Like Poles Repel -- Unlike Poles Attract
Have you ever used a compass?
A magnetic compass has a non-magnetic casing
(container). The compass needle is magnetic
and is free to pivot around in a circle. The
compass needle points to the earth's magnetic
north (which is a little different, but fairly
close to the location of the North Pole.)
A magnetic compass works
through air, water, glass, and walls.
The Magnetic Compass Points Towards Magnetic North
Magnets were first discovered near the ancient
Asian city of Magnesia. Certain stones had
special characteristics. These stones were
called magnetite. When suspended from a string these
rocks always pointed north. Asian sailors
began using these stones as compasses
when they traveled on voyages.
The Earth itself is a magnet and contains
a great deal of iron. On the other hand the
Earth's moon is largely made of aluminum,
not iron. The moon does not act like a
magnet and magnetic compasses do not
work on the moon.
In the experiment you created a chain of
paperclips. How could this happen? The
magnet wasn't touching most the paperclips.
Magnets can "magnetize" iron, steel (which
is largely made of iron) and certain other
metals with iron-like compositions.
This is called "induced magnetism".
The Paperclips Become Magnets Through Induced Magnetism
Scientists believe that the smallest
particles of iron in an object are each small
magnets that point in various directions.
When the object is magnetized these magnetic
particles all line up in a specific direction.
Now the combined strength of these particles
make the magnetism stronger.
Magnetized Particles Are Aligned
Magnetite is different. It is a natural magnet.
Another magnet does not magnetize magnetite.
Magnetite rocks have been in the ground for
thousands of years. Scientists believe the
Earth's own magnetism may slowly align the
tiny iron particles in these rocks. Over thousands
of years the Earth may be able to make magnets
out of materials containing large amounts of iron.
The effects of a strong magnet can be felt some
distance away from it. This space around a
magnet is called its "magnetic field".
Believe it or not, there is a connection
between electricity and magnetism. An
electric current produces a magnetic field!
The Danish physicist H. C. Oersted first
discovered this relationship.
The French physicist Ampere, determined
magnetic field strength could be increased
when the electrical wire was wound into a coil.
Winding the wire around a soft-iron core can
increase magnetic strength hundreds or
thousands of times. Such a device is
known as an electromagnet.
Advantages of an electromagnet over a
natural magnet include strength and the
ability to control the current and direction.
Have you ever seen salvage yard cranes?
These cranes use a lifting magnet to move
tons of scrap metals and old cars. A large
circular disk hangs from the crane. The disk
is a lifting electromagnet. Lifting magnets
are also used to load machine parts, steel rails
and scrap iron or steel. How does it work?
A switch controls the current which goes
to the electromagnet. The crane
switches the current on to pick up materials
or off to release them.
Some lifting magnets can carry 200 pounds
for ever square inch of the usable surface of the magnet.
Even some burglar alarms use magnets. A
magnet is attached to one side of a doorway or
window while a metal bar is attached to the door or
window frame. The metal
bar attracted by the magnet holds a switch
in place. As long as the door or window is
closed the magnet holds the metal bar and
switch in place and the alarm stays off.
If the door or window is opened the connection
between the magnet and the metal is broken
(just like when you removed the top paperclip
from the magnet in the experiment). The metal
bar no longer holds the switch in place and the alarm goes off.
Click To See The Movie
REFERENCES:
Branley, Franklyn M., What Makes A Magnet, Harper
Collins Publishers, New York, 1996.
Freeman, Ira M. and Durden, William J., Physics Made Simple,
Doubleday, New York, 1990.
Macaulay, David, The Way Things Work, Houghton Mifflin Company, Boston, 1988.