A2L Item 101

• Description: Identify the correct motion of a spool pulled by a string passing over the top of the central axle.
• Goal: Reason with rotational dynamics.
• Source: UMPERG-ctqpe136
• Keywords: Mechanics, 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 top of the axle, the spool will

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

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Commentary for teachers:

Answer

(1) For many students this remains counterintuitive.

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