Rotational Inertia Wands

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(A)Mechanics - A+25: Rotational Inertia

ASCO Rotational Inertia Wands, (1 meter long and 4 cm wide), are designed to show how the distribution of mass in an object determines the object’s rotational inertia (moment of inertia). The blue inertia wand has masses installed at both ends of the tube. The red inertia wand has masses installed near the grip at the center of the wand. These wands can be used theatrically by inviting a very strong student to sway the blue rod and inviting a relatively weak student to sway the red rod. The red rod is so much easier to move that it will rotate back and forth much faster.
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A+25+15
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A+30+0 Minor's apparatus: Movable discs rotated by falling weight.

Comments

James Little

Thu, 08/13/2015 - 17:01

The two wands are in Section B of Le Conte near the Helium tank.

James Little

Thu, 10/01/2015 - 09:37

You need two participants to do this demo. Tell them that the weight of the wands is identical and demonstrate the back and forth motion yourself. You can ask them which of them they think can get the wands waving faster. Traditionally you hand the red wand to the smaller participant and the blue want to the larger. The moment of inertia is so different that even a 6 year old can get the red wand moving faster than an adult. When it's done ask them why they think the wands behave so differently (fortunately or un the wands do have holes in the side of the plastic so they can see the weight distribution if they look carefully. As always when you present a demo make sure you ask the participants questions before you demonstrate and after. Think about the concepts involved beforehand; having a friend ask you questions about it can be very revealing as to if you understand it well or not. Whenever you ask a question count to five (or at least three) in your head waiting for an answer before you stay anything else.