Coefficient of Static Friction on a Turntable

AI Thread Summary
The lab aims to determine the coefficient of static friction between a metal washer and both metal and rubber surfaces by measuring the RPM at which washers fly off a turntable at varying distances from the center. Data indicates that the coefficient of static friction is lowest at medium distances for both surfaces, with the highest coefficient for the rubber surface occurring at the shortest radius and for the metal surface at the largest radius. The participant seeks clarification on these unexpected results, particularly why the coefficients behave differently across distances. They express uncertainty about their methodology and request assistance in understanding the findings. The discussion highlights the complexities of friction coefficients in dynamic systems.
jhawks8
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I'm doing a lab for my technical dynamics class and that lab is to determine the coefficient of static friction between a metal washer and both metal and rubber surfaces.

I did the experiment using 3 washers set at different distances from the center of the turntable as instructed, and recorded the RPM at which the washers of each distances flew off the turntable. My data is below:

Rubber Surface
r(m) |RPM |w(rad) |µ | AVG µ
0.03 |123 |12.88 |0.507|
0.03 |154 |16.13 | 0.796| 0.676
0.03 |147 |15.39 |0.724|

0.06 |100 |10.47 |0.671
0.06 |97 |10.16 |0.631 |0.607
0.06 |88 |9.22 |0.52

0.1 |71 |7.44 |0.564
0.1 |80 |8.38 |0.716 |0.647
0.1 |77 |8.06 |0.662

Metal Surface

r(m)|RPM |w(rad) |u...|AVG µ
0.06 |77 |8.06 |0.397
0.06 |67 |7.02 |0.301 |0.376
0.06 |80 |8.38 |0.43

0.08 |62 |6.49 |0.344
0.08 |62 |6.49 |0.344 |0.363
0.08 |67 |7.02 |0.402

0.1 |61 |6.39 |0.416
0.1 |61 |6.39 |0.416 |0.403
0.1 |58 |6.07 |0.376

What is not making sense to me is why the coefficient of static friction is the lowest when in the medium distances. Also, the largest coefficient for the metal surface is the largest radius, and the largest coefficient for the rubber surface is the shortest radius.

I need help understanding this, or if I'm doing something wrong and I don't know it. Any help is really appreciated.
 
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Sorry for the sloppy tables.
 
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