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Rotational Motion change angular rotational

by physgrl
Tags: circular motion, torque
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physgrl
#1
Oct31-11, 11:25 AM
P: 138
1. The problem statement, all variables and given/known data

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

2. Relevant equations

n/a

3. The attempt at a solution

I would like to understand why b is the correct answer.
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dacruick
#2
Oct31-11, 12:11 PM
P: 1,084
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.
physgrl
#3
Oct31-11, 12:30 PM
P: 138
Got it...thanks!!

dacruick
#4
Oct31-11, 12:36 PM
P: 1,084
Rotational Motion change angular rotational

Quote Quote by physgrl View Post
Got it...thanks!!
Awesome. youre welcome


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