Starring
You and Your Students!
Script By
Vicki Cobb, Education World Science Editor
Synopsis
Teach about properties by passing a coin through a solid.
Genre
Chemistry, Technology
Required Props
- a quarter
- a lipstick tube or other small cylinder with a diameter about the size of a quarter, but smaller
- a thin latex glove (the kind used by doctors and dentists)
- scissors
- a small clear jar
- a rubber band
Setting the Scene (Background)
Do you silently moan and groan when you have to teach properties of matter? Generalizations that seem unrelated to daily life (state of matter, density, color, and so on) are boring to learn about and are boring to teach. But a property of a particular kind of matter becomes fascinating when it is unusual and allows you to do something unexpected or magical…
Everyone knows a solid can't pass through a solid. But, with a little preparation, you can make a quarter appear to pass through a solid latex membrane. Suddenly, properties of matter become a topic worthy of attention!
Stage Direction
This is close-up magic that requires you to prepare ahead of time without
any students watching. This demonstration is most effective when done
with a small group standing around you. The kids will want to know how
you did what you are about to do; letting them in on the secret is where
the lesson becomes powerful.
Plot
Act I: The Set-Up
- Place the coin, heads up, on top of a small cylinder such as a lipstick tube that is standing on a tabletop. Remember, the coin should be only slightly larger than the diameter of the tube.
- Cut the glove open near the thumb to make a large piece out of the palm and back. Rinse off the inside of the rubber glove to get rid of its coating of talcum powder.
- Stretch the palm part of the glove over the coin by pulling down evenly in all directions. Stretch the latex thin enough so that the image on the coin is clearly visible. (Warning: Don't pull too hard or the latex will tear.)
- Now ease off the pressure. The latex will trap the coin, and it will appear to be sitting on the top surface of the latex.
- Stretch the glove gently over the mouth of a small jar, being careful not to dislodge the coin. Fasten the glove with a rubber band. The coin, which is really on the underside of the rubber, looks as if it is sitting on top of it.
Act II: The Performance
Now invite your audience over to watch. Claim that you can make the coin pass through the latex without making a hole in the latex. Give the coin a tap from above. It will drop like a shot into the jar, leaving the latex undamaged.
Behind the Scenes
The property of latex that allows you to do this trick is its elasticity. Latex is a material that has a memory. You can bend it or stretch it, but when the distorting force is removed, the rubber returns to its original shape. You're exploiting this property twice in this trick.
- The round shape of the coin is a key element in trapping it in the rubber. When the rubber is stretched over the rim of the coin and then released, the latex underneath the coin pulls together to form a ring that holds the coin in place.
- When you release the coin with your tap, the latex that was underneath the coin is then free to return to its original flat, un-stretched state.
Materials engineers are always looking for applications that take advantage of a material's unusual properties.
Article By Vicki Cobb
Education World®
Copyright © 2005 Education World
04/15/2005
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