Friction of Pivot: Torque Calculation

[H_man]

Hi,

I just wanted to verify that the Torque that the friction of a pivot would exert against the oscillation of a pendulum was:

Torque = \mu m g r

Where \mu is the coefficient of friction, m is the total mass that is being supported by the pivot and r is the radius of the axis/rod that is supporting the pendulum. So the rod turns in the pivot as the pendulum oscillates.

So far I have only found one online link to this and it doesn't seem to be discussed in any of the mech. books I've been looking through.

 

[FredGarvin]

That would make the most sense if you are assuming that the sliding friction is the only source.

 

[H_man]

Well, the pendulum is in a vacuum chamber so I can completely ignore viscous friction... this is clear from the motion, the way the damping occurs, ie linear as opposed to exponential.

Can you think of any other sources??

Thanks for your help