Physics Help Forum Friction of rotating disks

 Periodic and Circular Motion Periodic and Circular Motion Physics Help Forum

 Aug 28th 2018, 12:29 PM #1 Junior Member   Join Date: Aug 2018 Posts: 1 Friction of rotating disks Two disks are laying on top of each other. The disks are rotating on the same axis, are made of different materials (different friction coeffs), and are rotating at different velocities. The aforementioned are all given in the problem. Is there an equation to calculate the energy lost due to friction between the two disks over a specific amount of time or distance traveled? I don't need someone to solve this problem but am curious to see if there is a given equation(s) that can be applied to a system like this.
 Aug 28th 2018, 09:35 PM #2 Senior Member   Join Date: Apr 2017 Posts: 484 Since these are discs rotating on the same axis (we are not told this azis is in the center of disc), then the relative velocity of the friction surfaces will vary in proportion to distance from axis ... Energy loss is proportional to velocity and coefficient of friction . Integration is required topsquark likes this.
Aug 29th 2018, 12:20 AM   #3
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 The disks are rotating on the same axis, are made of different materials (different friction coeffs),
Are you sure this is what your question says?

I ask because the statement is meaningless.

A friction coefficient is defined as between two bodies, which may be of different materials. So 'rubber on concrete' is different from 'steel on concrete' or 'steel on steel'.

So there can only be one coefficient of friction.

Now consider the rest of the mechanics.

The frictional force will be proportional to the contact reaction between the two bodies.
So you need to know more than just "laying one on top of each other" - how can that be, they can't be both on top.

You will have to be much more precise in your thinking and wording if you want to solve this. Success in Physics is the result of precise thinking not just flinging formulae about.

 Tags circular motion, disks, friction, rotating

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