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Torque of a wheel in space 
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#1
Feb509, 09:37 PM

P: 22

I know if I apply a force(perpendicular to he radius) to a wheel to rotate it, I am applying a torque. I change the wheel's angular acceleration, thus creating a torque.
I can find the direction of a torque via the right hand rule. If there is a wheel spinning in space where there are no forces acting on it, does the wheel still have a torque? ([tex]\tau[/tex] = L[tex]\alpha[/tex]) Doesn't the wheel still have an angular acceleration? I'm afraid I've been thinking about all of this too much and am beginning to confuse myself. 


#2
Feb509, 10:11 PM

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P: 22,302

In space or not, if there is no force acting on a wheel, there is no torque and no angular acceleration.



#3
Feb509, 10:18 PM

P: 22

ok, I think I was getting the linear acceleration and angular acceleration confused.
A spinning wheel will have centripetal and tangential acceleration, but it will not have angular acceleration b/c there is no change in angular velocity. So not all spinning objects have angular acceleration or torque. 


#4
Feb609, 05:28 AM

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P: 22,302

Torque of a wheel in space
Correct, with the caveat that I wouldn't say "the wheel" has a centripetal acceleration  different points on the wheel will have different centripetal acceleration and a point at the center will have none.



#5
Feb609, 06:30 AM

P: 4,512

Push on the center of mass of an object with a force, and you've applied torque. Doesn't sound as if it makes sense does it?
Torque is defined as a force acting about a point. You can choose any point you like. It doesn't have to be the center of mass. If the force is one pound, and the point of interest is one foot from the line of force, the torque is one footpound. Take a wheel that is at rest and not spinning. If you push on the rim, it will both spin and obtain a translational velocity. If you don't want it to give it a velocity, you apply an equal and opposite force on the opposite side of the rim. This is called a Force Couple. It's the intuitive idea alot of use have about what is torque, before we lean the weird definition. 


#6
Feb609, 09:33 AM

P: 288




#7
Mar209, 10:00 PM

P: 328

So, many thanks to the jerk who decided against calling it tangential speed. 


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