Rotational Motion change angular rotational

  • Thread starter physgrl
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  • #1
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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.
 

Answers and Replies

  • #2
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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.
 
  • #3
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Got it...thanks!!
 
  • #4
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