Friction between rotating objects

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The discussion focuses on calculating friction between two rotating objects, specifically a plate rotating on a table. It highlights the need to understand how to apply the coefficient of friction in this context. The suggestion is made to divide the plate into concentric ring-shaped segments, which behave similarly to straight rods under friction. The integration over the surface using spherical coordinates is proposed as a method for calculation. The participants express gratitude for the insights shared, indicating progress in solving the problem.
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In physics, we learned about friction between one object sliding across another, but when we got to torque and angular velocity, etc, there was never any mention of how to calculate friction between 2 objects rotating in place. Say you have a plate on top of a table and it is rotating about the center of the plate. How would you calculate the friction between the plate and the table if the coefficient of friction is known?
 
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change to spherical coordinates and integrate over the surface.
 
malawi_glenn said:
change to spherical coordinates and integrate over the surface.

Yes … specifically, if you divide the plate into concentric ring-shaped bits, each bit of length 2πa will have the same behaviour under friction as a straight rod of the same mass and of length 2πa. :smile:
 
Thank you guys for your help. I am going to see if I can figure out this problem I was working on now
 

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