Unlikes attract, Likes repel
Introduction
Two magnets can attract each other or repel each other depending on how they are oriented.
Material
Assembly
Remove the string used in the Where's North activity from the magnets leave the dots on.
To Do and Notice
Bring the magnets near each other and feel the
forces they exert on each other.
Turn one of them until it is attracted by the other. Let them come
together slowly until they touch. Release one magnet. The other will
attract it strongly enough to hold it in place against gravity.
Rotate one magnet to find the position in which it is most strongly
repelled by the first magnet.
Let the magnets attract one another again.
Rotate the other magnet until the two magnets repel each other.
Note the attraction and repulsion of the magnets when two "dot" faces
are close together.
Notice it when two "nodot" faces are together.
Notice it when a "dot" faces a "nodot."
Fill-in the following table with the words attraction or repulsion. Such a table is an important way to keep track of scientific data
|
dot |
nodot |
|
|
dot |
? |
? |
|
nodot |
? |
? |
A compass is a magnet which is pivoted and free to
rotate. Hold the compass away from all magnets and look at it. The
red end of the compass needle points toward the north geographic pole
of the earth. (This end of the compass was originally called the
north seeking pole. Its name was eventually shortened to the north
pole of the compass.)
Bring the compass near one of the magnets, the red end of the compass
is its north pole and will be attracted to the south magnetic pole of
the magnet. The red end of the compass needle will be repelled by the
north pole of the magnet. Identify whether your dot is a north pole
or a south pole by using the compass. Redo your table replacing the
names dot and nodot with the names north and south.
What’s Going On?
The north pole of one magnet attracts the south
pole of the other, and vice-versa.
This is the origin of the expression: "unlike poles attract". (Dots
attract nodots)
When two magnets are allowed to approach, unlike poles attract, if
they are allowed to rotate freely they will rotate until the unlike
poles are next to each other.
The north pole of one magnet repels the north pole of the other
magnet, likewise the south poles repel. This is the origin of the
phrase,"like poles repel."
|
North |
South |
|
|
North |
repel |
attract |
|
South |
attract |
repel |
So What?
One pole of your magnet pointed north, such a pole was originally called a north seeking pole which was eventually shortened to north pole. When it was discovered that the earth was a magnet the north pole of the compass was attracted to the opposite magnetic pole on the earth. Unfortunately this magnetic south pole was located in the northern hemisphere of the earth. So we ended up with the magnetic south pole near the geographic north pole. This has caused confusion ever since. In fact even today the magnetic south pole of the earth is marked on maps as the "north magnetic pole." Beware!
Etc
Peter Perigrinus made spheres from naturally magnetic lodestone in 1269. These stones were composed of magnetite, Fe3O4. Small iron rods sprinkled onto this sphere clustered around and formed a radial spoke pattern around two points on opposite sides of the sphere. This is just like lines of longitude which radiate from the two poles on a map of the earth. The similarity between the magnetic sphere and the earth sphere inspired the name of "polus" or today "poles" for the two ends of the magnet. The pole of a magnet which was attracted to the north pole of the earth became known as the Boreal or north seeking pole, which was later shortened to north pole. In 1600 William Gilbert noted that the earth was a magnet with poles of its own. The basic rule that “opposite poles attract” means that the magnetic pole of the earth that is currently located near the north geographic pole of the earth is actually a magnetic south pole. (To add to the confusion, geologists call this pole the North magnetic pole.)
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Scientific Explorations with Paul Doherty |
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30 May 2000 |