
#1
Sep613, 06:10 AM

P: 7

Hello,
If I apply force on a rigid cube, I can find the torque τ as: τ = F x r Now, from torque τ I can know about the axis of rotation but how much should I rotate the cube. How can I find the angular velocity ω from torque τ? Or is there any other way by which I can find how much the object rotates every second? Thank you. 



#2
Sep613, 06:19 AM

HW Helper
Thanks
P: 5,552

What do the equations of angular motion tell you?




#3
Sep613, 07:00 AM

P: 7





#4
Sep613, 12:12 PM

HW Helper
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P: 5,552

How to find angular velocity from torque?
If you study the equations of angular motion, you'll see that for a body rotating with a constant angular velocity, there is no net torque applied.
It's analogous to a spaceship travelling at a constant linear velocity: there is no net force being applied to the spaceship. Force and torque accelerate objects from one velocity to another, so when these are applied, the velocity is always changing. 



#5
Sep613, 07:13 PM

P: 7

So, how do I find the amount by which I should rotate an object every second if I know the torque of an object?




#6
Sep613, 07:57 PM

HW Helper
Thanks
P: 5,552

You can calculate the amount of torque required to accelerate the object, say from rest to a certain angular velocity.
Your question is a bit unclear. If you want to determine what the angular velocity of a rotating object, that can be accomplished by using a stroboscope or timing light. 



#7
Sep713, 05:57 AM

P: 7





#8
Sep713, 09:35 AM

P: 49

(torque) = (moment of inertia).(angular acceleration) ζ=Iα also α = dω/dt or dω/dt= ζ/I and at last ω = ∫ (ζ)/(I) . dt even if ζ is time dependent calculate ω, [caution do not forget integration constant i.e. initial angular velocity] as per your question ζ=Fxr put it in the integrating equation 



#9
Sep713, 10:18 AM

Mentor
P: 14,459

This is fine for a cube because the momentum of inertia of a cube, like a sphere, can be treated as a scalar. This is not true in general. The moment of inertia is tensorial in nature. If you don't know what that means, that's okay if this is for a lower level (freshman/sophomore level or below) physics class. Those lower level physics classes steer clear of cases where this tensorial nature rears its ugly head.




#10
Sep813, 01:10 AM

P: 49

Phd!!! mann! you are awesome at vocab and physics 



#11
Sep813, 05:44 AM

Mentor
P: 14,459

It's the second or third year in college where one learns that moment of inertia is a tensor rather than a scalar. With regard to grammar, get in the habit of writing complete sentences. It's a rule of this site, and it's also a rule in life beyond college.




#12
Sep913, 04:25 AM

P: 49

like current is tensor quantity which is having some direction (lol! I dont know exactly but yeah i wanna ask is time also tensor quantity) i when studied electricity at coaching at beginning of my 9^{th} this year i opposed teacher by saying example of time but not confirm 


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