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Magnetic Globe
P8-1130
BACKGROUND:
The magnetic globe was invented by Dr. Paul Doherty, director of The Teacher Institute at the
Exploratorium in San Francisco. It is now produced by Arbor Scientific so that other teachers can use
Paul‟s teaching tool in their own classrooms.
BACKGROUND ON THE EARTH’S MAGNETISM:
“The earth acts like there is a large bar magnet placed near its center. However, the earth is not a
magnetized chunk of iron like a bar magnet. It is too hot for individual atoms to remain aligned.
Currents in the molten part of the earth beneath the crust provide a better explanation for the
earth=s magnetic field. Most earth scientists think that moving charges looping around within the
earth create its magnetic field. Because of the earth‟s great size, the speed of moving charges
would have to be less than one millimeter per second to account for the field. Another candidate for
the earth‟s magnetic fields is convection currents that result from heat rising from the earth‟s core.
Earth‟s heat comes from the release of nuclear energy C radioactive decay. Perhaps such
convection currents combined with the rotational effects of the earth produce the earth‟s magnetic
field” (Hewitt, 562-563).
Whatever the cause, the magnetic field of the earth is not stable, but rather has been wandering
around throughout geological time. Geologists know this by studying rock containing iron. Just
before the rock solidified, its iron content lined up with the earth‟s magnetic field. Geologists can
now date the rock and analyze what direction the iron is pointing in. That‟s where the north and
south magnetic poles of the earth were at the time the rock was formed. Right now the magnetic
poles are somewhere over the Hudson Bay region of northern Canada and just south of Australia.
“What‟s the largest magnet in the world?” Answer: “The world, of course!” Be prepared, this
confuses a lot of people—even people who know how a magnet behaves. Most people‟s confusion
seems to lie in the fact that they usually look at magnetic fields from the outside. They need to
understand that they are standing in the middle of a field, created by the earth, right now.
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To help conceptualize it, visualize the magnetic field lines created by a bar magnet (see picture
above left.) Now place a globe in the center of the magnetic field (see picture above right.) We exist
on the outside surface of the earth, where the field is curved. It helps to visualize yourself with a
compass standing on the globe in the picture. What direction would the compass point in? When
you think about it from this vantage point, compasses behave quite understandably.
PRODUCT INFO:
The Magnetic Globe consists of a powerful magnet inserted into a “squeesh” globe. Since the earth
essentially behaves like it has a giant bar magnet at its center, the Magnetic Globe offers a unique
opportunity to view the earth‟s magnetism from the “outside.”
ACTIVITIES:
What would a compass do at the north pole?
1. Take several used staples and place them on the globe. The magnetic force of the globe is
strong enough for them to act like compasses and line up with the field.
2. At the equator, they lie flat, pointing to the north and south poles.
3. Push a staple to the north a bit. Notice that while it still points to the north pole the other tip
is starting to point out into “space.” You can explain this with the help of the globe and field
diagram above. The angle at which the staple is leaning is called the field‟s “inclination.”
4. Move the staple to where it stands straight up and down. This is your Magnetic Globe‟s
magnetic north pole. A compass, if taken to the north pole, would try to point directly down.
However, they are restricted by their encasement to two dimensions and would have a hard
time pointing down or up.
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ANN ARBOR, MI 48106 T 800-367-6695
WWW.ARBORSCI.COM
©2009 ARBOR SCIENTIFIC ALL RIGHTS RESERVED
5. With your finger, push the same staple to the magnetic south pole. What is the difference?
What is „inclination‟?
1. Since the staples seem to point up and down at certain angles depending on where you are
at on the globe, why don‟t compasses do that?
2. Again, compasses are restricted to 2 dimensions. There is enough of a “northern” aspect to
the magnetic force to get a compass to point north.
3. To demonstrate the inclination of the earth=s field you need a three dimensional compass.
Try Arbor Scientific‟s Magnaprobe. It is a gimbal-mounted bar magnet that floats freely
enough to line up with any magnetic field in three dimensions.
4. Hold the Magnaprobe at arms length and way from any magnetic forces. If the earth=s field
is strong enough, it will line up correctly, displaying the inclination. It will point “roughly”
north and south, but also, up and down. Compare the results with a two dimensional
compass.
5. Next, hold the Magnaprobe up to the Magnetic Globe to where your class room is located on
the map. The inclination should be close to the same.
What are the Van Allen radiation belts?
1. Use Arbor Scientific‟s Magnaprobe to map out the Magnetic Globe‟s surrounding magnetic
field.
2. The Van Allen radiation belts are charged particles that get trapped in the earth‟s magnetic
field. They move back and forth between the magnetic north and south polar regions. These
trapped particles interact with the earth‟s atmosphere to produce the dazzling spectacle of
the aurora.
RELATED PRODUCTS:
The Magnaprobe (P8-8005) is a gimbal-mounted bar magnet that acts as a three dimensional
compass.
BIBLIOGRAPHY:
Conceptual Physics by Paul G. Hewitt. Pearson Education, Inc.
PO Box 2750
ANN ARBOR, MI 48106 T 800-367-6695
WWW.ARBORSCI.COM
©2009 ARBOR SCIENTIFIC ALL RIGHTS RESERVED