You and Your Students!
Vicki Cobb, Education World Science Editor
Discover invisible ridges on a refrigerator magnet.
Setting the Scene (Background)
I love to discover something new and different about common things. What could be more common than a refrigerator magnet?
Magnetism is a mysterious force that attracts and repels across a distance. Kids love to play with magnets, so here's a new way for them to fool around with them.
Cut a flat rubber magnet in half. Press the unprinted sides together. Depending on how you put them together, one of three things will happen: the pieces
--- don't stick together,
--- they stick together weakly, or
--- they stick together strongly.
If the pieces do not stick together, rotate one piece 90 degrees; then the pieces will stick together either strongly or weakly.
When the pieces stick together, rub the two pieces back and forth against each other. What do you notice? (they feel rough, they feel as if they have ridges)
Place a piece of white paper over the magnet and sprinkle it with iron filings. The filings will form a pattern over the magnetic rows beneath the paper.
Behind the Scenes
A magnet is made from a material that can attract pieces of iron and other magnetic materials. If a bar-shaped magnet is suspended so that it can swing freely, it will line up with one end pointing north and the other pointing south. The end pointing north is its north pole; the end pointing south is its south pole.
Flexible magnets are unlike that solid bar magnet. The flexible magnet is made of many rows of tiny bar magnets embedded in a rubber sheet. Rows of poles that point north alternate with rows of poles that point south. The rows are about 1/8 of an inch apart.
When the rows are at right angles, they don't line up, so the attraction is too weak to form a bond. The magnets' surfaces move smoothly past each other.
When the two pieces of the magnet are aligned so that the magnet rows are parallel, you feel the corrugation as you pull them across each other. The jerky motion is caused when like poles repel each other and unlike poles attract each other. Your senses of touch and hearing interpret that as a rough surface.
You can see where the rows of magnets are in a rubber magnet when you sprinkle iron filings on the sheet of paper over the magnet.
For more on magnetism, check out my book Sources of Forces: Science Fun With Force Fields. illustrated by Steve Haefle.
Article By Vicki Cobb
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