Wheres the Rub?

Starring

You and Your Students!

Script By

Vicki Cobb, Education World Science Editor

Synopsis

Discover invisible ridges on a refrigerator magnet.

Genre

Physical Science

Required Props

• refrigerator magnets (The plastic or rubber kind. The ones used for advertising are the best, and they're often given away free. Dollar stores usually have them too. Or you can ask students to bring them in. Note: Students will be cutting them up so they cannot be returned.)
• scissors
• white paper sheets
• iron or steel wool filings (You can get iron filings through a chemical supply house; or you can make them by using scissors to cut up very fine steel wool from a hardware store. The steel wool should not have soap in it.)

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.

Show-Biz Science is scripted by popular children's book writer Vicki Cobb. Click to learn more about Vicki or to read a brief synopsis of her philosophy of teaching science. Visit our archive of archive of Show-Biz Science Activities. Watch for a new activity each week. Then chat with Vicki -- share your feedback and ask your questions about teaching science -- on our special Showbiz-Science message board. Be sure to visit Vicki's Kids' Science Page for more great science fun, a complete list of her books, and information about how you can invite Vicki to come to your school. And don't miss her library of science videos too. Or visit Vicki and other great authors of nonfiction for children at the INK Think Tank.

Plot

Act I
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)

Act II
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.

The End

For more on magnetism, check out my book Sources of Forces: Science Fun With Force Fields. illustrated by Steve Haefle.

Article By Vicki Cobb
Education World®
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