Rotational Motion change angular rotational

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Homework Help Overview

The discussion revolves around a question related to rotational motion and the conditions under which a force can change angular rotation. The subject area includes concepts of torque and angular momentum.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore why certain options (a and c) do not lead to a change in angular momentum, focusing on the role of torque and the geometry of force application.

Discussion Status

Some participants have provided insights into the reasoning behind the correct answer, discussing the implications of applying force through different points relative to the axis of rotation. There is an acknowledgment of the mathematical relationships involved, particularly regarding torque.

Contextual Notes

The original poster seeks clarification specifically on why option b is considered correct, indicating a focus on understanding the underlying principles rather than simply identifying the answer.

physgrl
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Homework Statement



9. A force can change angular rotational if it acts through:

a. the axis of rotation

*b. a lever arm tangential to the direction of rotation

c. a moment arm parallel to the axis of rotation

d. none of these

Homework Equations



n/a

The Attempt at a Solution



I would like to understand why b is the correct answer.
 
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I guess we could start with why it isn't a or c. Angular momentum is changed when Torque is applied. If you apply a force through the axis of rotation, then r is 0. if you apply force through a moment arm parallel to the axis of rotation then torque is also zero since

τ = F x r
|τ| = Frsinσ

since F and r are parallel, the angle is 0, therefore the torque is 0. If you applied it tangentially, then the σ value will be 90 and sinσ will be 1.
 
Got it...thanks!
 
physgrl said:
Got it...thanks!

Awesome. youre welcome :smile:
 

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