How Does Friction Affect Torque in an Atwood Machine?

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SUMMARY

The discussion focuses on calculating the net torque acting on a pulley in an Atwood machine, specifically addressing the impact of friction between the pulley and the rope. The net torque is derived from the difference in tensions (T1 and T2) acting on the pulley, leading to the equation τnet = (T1 - T2)r. The contributor initially confused the direction of the tensions but clarified that both tensions should point downward, confirming the correct formulation of the torque equation.

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Homework Statement


Two masses are suspended from a pulley of mass m supported by an axle (Atwood machine).
What is the net torque acting on the pulley wheel in terms of T1 and T2?

There is friction between pulley and rope.
Ropes are massless and pulley can rotate without friction about its own wheel.

Homework Equations


τ = I*α

The Attempt at a Solution


This is what I got so far:
http://img685.imageshack.us/img685/4333/24667502.th.png

Others get τnet = (T1-T2)r
Why??

Thanks in advance!
 
Last edited by a moderator:
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Wait nevermind, I just realized that both tensions should be pointing downward.

So, (T1-T2)=r is correct.

Thanks anyways!
 

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