Demos: 1Q-05 Weighted Batons

Two batons, having the same mass, are weighted so that one has a greater concentration of mass at the center, whereas the other’s mass is more concentrated at each end. In attempting to rotate the batons about their centers, it is found that the one weighted at the ends is more difficult because of the greater rotational inertia.

Directions: First establish that the masses are equal. This can be done by placing the batons on a scale, or more qualitatively, by having a student hold each and see that the the masses feel the same. The baton should be rotated by grasping it at its center and “wiggling” it back and forth as quickly as possible.

Suggestions for Presentation: A popular presentation of this demonstration is to tell the students that you are going to have try-outs for the Purdue Golden Girl. (This pretty much dictates using females, but you can adjust the presentation accordingly if you wish to use a male.) Choose a student and hand her both batons to see if they appear to weigh the same. Then take back the red one and ask the student to grasp the blue baton at its center and wiggle it back and forth as quickly as possible. Demonstrate what you want by your doing the same thing with the red one. Encourage the student to do it as fast as possible. (A little fun derision is in order here. The fact that you can wiggle your baton so much faster demonstrates your superiority in this matter.) Then exchange batons and repeat the process. Ask the students if they can suggest a reason for the results.

Applications: Center weighting vs end-weighting can be translated into such things as flywheels.

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