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Cackling, Crowing Cup!
Objective: To amplify sound waves using very simple equipment.
Materials:
Paper Cup
Push Pin
String
Paper clip
Water
Paper Towel
Procedure:
1. Use the push pin to poke a hole in the bottom of the cup. Make the hole
big enough to thread the string through the hole.
2. Thread the string through the cup. Tie the paperclip to the end of the string
on the outside of the cup, so that when you pull the string through, the
paper clip will be on the bottom of the cup.
3. Fold your paper towel so that it’s a rectangle about 2 inches by 1 inch
(very approximate is fine).
4. Wet the paper towel with water and squeeze most of the moisture out.
Now for the tricky part:
5. Hold the cup upside down in one hand, with the string dangling down
towards the floor. Hold the damp paper towel in the other hand.
6. Firmly grasp the string with the damp paper towel. Jerk the paper towel
down the string, so that the paper towel slips along the string. If no sound
is produced, dampen the paper towel a bit more and try again. With
practice, you’ll get that string howling!
What’s Going On?
What we’re doing here is amplifying sound—producing the sound the string
would make anyway, but making it louder. All sound comes from vibration. Here,
the string is vibrating, and that gets the air inside the cup vibrating. The shape of
the cup helps to amplify the sound. HONK!
Think and Talk About This:
Different materials can do a better job of amplifying sound waves. What do you
think would happen if you tried this experiment at home with a tin can instead of
a paper cup? Try it with Mom/Dad’s help!
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