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Science
Activity
"One turn deserves another "
Materials
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 1 average size balloon (a clear balloon works best, but any balloon will do).
1 Nickel (or other smooth edged coin)
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Instructions
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Step 1
Put the nickel into the deflated balloon. Blow it up and tie it off.
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Step 2
Begin slowly rotating the balloon as shown. At first the coin may just bounce around. Just keep spinning the balloon faster and faster and the coin will begin spinning.
Once the coin is spinning, place the balloon onto a table top. Continue to hold the top of the balloon until the coin finally stops spinning.
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What happened?
Physics teaches us that all moving objects continue in a straight line unless a force is put on that object. If the balloon were not in the way, the nickel would just go straight out (gray arrow). But because the curved balloon is pushing against the nickel at an angle (blue arrow), the coin is pushed in a new direction (red arrow). This action is continually acting on the coin which causes it to go around the balloon. This inward force acting on an object to keep it moving in a curved path around a center point is called centripetal force. |
Explore further
This time spin the nickel in the balloon, but instead of putting it on a table top, gently toss it in the air. What happened?
You should have found that the balloon began to "wobble" while it was in the air. As the coin makes its revolution it pushes out against the balloon, causing it to wobble as it goes around. Planets orbiting a star can cause the star to "wobble" similar to the balloon. Sometimes new planets are found this way. Scientists will observe that a star (like our sun) has a "wobble". They then look for a planet that might be causing this. The star wobbles because of the tug of the planet's gravity on the star as it orbits the star. |
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