Observations and results
In each cup, did the marble move from the middle of the cup to the bottom?

When an object moves, or accelerates, in a circle, the object wants to move out, away from the circle's center. Without the push of centripetal force, the object would move in a line, flying out and away from the center of the circle. For example, if you had let go of the cups when you were spinning them, they would fly away from you in a straight line. Each marble in the spinning cups also wanted to move away from you, away from the circle's center, and so each marble should have traveled through the Jell-O and ended up at the bottom of the cup.

In this activity, centripetal force acting on the system is supplied by the tension in the string. This force kept the cups moving in a circular path. This is a "pull" force, similar to how satellites are kept in orbit due to the pull of Earth's gravity. A "push" centripetal force acted on the marble: this force, supplied by the bottom of the cup, kept the marble going in a circular path and not flying away in a straight line. A push centripetal force also keeps you in your seat on a loop of a loop-de-loop roller-coaster ride and when you're making a turn on your bicycle.

Cleanup
Throw the Jell-O in the trash when you are done, after retrieving your marbles!

More to explore
Centripetal Force from the Georgia State University, Department of Physics and Astronomy
Newton, an Apple and You from Light-Science.com
Roller Coaster Science: Marbles, Tubes and Loops from Science Buddies
Centripetal Force from Science Buddies

This activity brought to you in partnership with Science Buddies

3 Comments

1. 1. kieryn 04:01 PM 7/12/12

   Um. As anything involving jello, much fun. Maybe a little overkill though?
   
   For a more boring, but less time-consuming experiment you can tie a small object to a length of elastic cord and observe that as you spin the object around faster the longer the elastic is stretched due to the extra force.
   
   Hmmm. Maybe this is why I am not a 3rd grade science teacher.

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2. 2. dadster 05:33 PM 7/12/12

   Good illustration .But a video of the experiment would have made the effort ten times more interesting and attention-arresting .videos can communicate better than mere words only.

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3. 3. jack.123 06:16 PM 7/13/12

   The object here is to do the actual experiment yourself.Not just view someone else doing it.

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