Simple coefficient of friction question

[jmart157]

Here's my givens... i need to find the coefficient of friction on the material.

No load torque on motor - 3.19 Nm
Loaded torque on motor - 3.49 Nm
Surface area in contact with motor shaft - .1885"
Mass of loaded material on shaft - 17.16 lbs = 76.33 N
Rads/sec - 31.42Looking to find the coefficient of friction. I need formulas and assistance please, not answers :)

Also, if I need to get/provide more information, I believe I can.

Jon

 

[jmart157]

alright, this came too easy. please confirm...

torque = Radius x force

which means rotational force = torque/radius

loaded rotational force = 41.83/2" = 20.92 lbsf
no load rotational force = 38.25/2" = 19.123 lbsf

resistive force from load = 20.92 lbsf - 19.123 lbs f = 1.7928 lbs

coefficient friction is (resistive force divided by rotational force) divided by 2

CoF = (1.7928/20.92)/2 = 0.0428

This seems realistic as this is plastic wearing against polished steel, in hot water. What do you guys think?