How Does Friction Affect Torque in an Atwood Machine?

AI Thread Summary
In an Atwood machine, the net torque acting on the pulley is influenced by the difference in tension between the two masses, represented as τnet = (T1 - T2)r. Friction between the pulley and the rope complicates the dynamics, but the pulley can still rotate without friction about its own axis. The discussion highlights the importance of understanding how tension affects torque, leading to the conclusion that both tensions should be considered in the downward direction. The final equation reflects this understanding, confirming that (T1 - T2) = r is correct. Overall, the relationship between friction, tension, and torque is crucial for analyzing the system's behavior.
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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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