A2L Item 102

• Description: Identify the correct motion of a spool pulled by a string passing along the bottom of the central axle.
• Goal: Reason with rotational dynamics.
• Source: UMPERG-ctqpe137
• Keywords: Rotational Dynamics, Torque

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The question for students:

A spool has string wrapped around its center axle and is sitting on a horizontal surface. If the string is pulled in the horizontal direction when tangent to the bottom of the axle, the spool will

1. roll to the right.
2. not roll, only slip.
3. roll to the left.
4. can’t be determined.

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Commentary for teachers:

Answer

(1) For many students this is really counterintuitive.

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