# Measuring Friction at a curved surface

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1. Apr 18, 2016

### bartrocs

Hi, if I have a block of metal with a quarter circle curve cut out of it, and a metal roller of matching radius that contacts this curved piece, what are some ways I could go about measuring the friction between these two surfaces? The roller is fixed and the block is pushed into it with a horizontal force. See the image for clarification:

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2. Apr 18, 2016

### Baluncore

The friction coefficient will be highly dependent on lubrication and surface contamination.

To measure the coefficient, Cfrict, you need to rotate the cylinder. The torque required, Ftorque, needs to be corrected for the radius, Ftorque / r, then the ratio with your Fapp computed.
Cfrict = Ftorque / ( r * Fapp )

3. Apr 18, 2016

### bartrocs

of course, I understand the theory, I was probably not clear enough but I am interested in the actual system of measurement, for example, if I had some motor driving a shaft with the drum on it. If I put a reactive torque (torsional) sensor inline between the drum and the motor, would that work to measure the frictional torque?

4. Apr 18, 2016

### Baluncore

Yes.
But if instead you attached the motor directly to the cylinder shaft, you could then measure the torque of the motor against it's mountings. The torque gauge is then not rotating, so you need no slip rings for instrumentation cables to the gauge.

5. Apr 18, 2016

### bartrocs

Perfect! I did not think of that. It would probably be a more cost effective solution as I could use force transducers on the mountings and measure torque that way. Thanks for your help

6. Apr 18, 2016

### Baluncore

The motor could be mounted on a shaft co-axial with the roller shaft. Then only one force sensor is needed at the far end of a torque arm attached to the motor casing. So simple.