Hello everyone, my question isn't exactly a "Here's the data how do I do it" but rather why is it giving me "this" answer.(adsbygoogle = window.adsbygoogle || []).push({});

I was doing a lab in class the other week, involving a pulley system which has one mass on a table and the other hanging. We had a balance to measure the masses and a motion sensor(timed for one second 5 times to get an average) to determine the acceleration. The objective to the lab was "to determine how the coefficient of kinetic friction depends upon the speed, surface area, and mass of a block sliding on a horizontal surface." Now correct me if I'm wrong but I thought that the coefficient of friction was independent and didn't vary for a particular surface? The data we collected ended up having different coefficients with the below equation.

Equation

uk(coefficient) = (m1g-(m1+m2)a)/(m2g)

Taken data and plug n chug

One example of data we took was m1(hanging mass)=.05kg, m2(sliding mass)=.05kg and a(acceleration)=.563m/s^2

Now I plug this into the equation:

(.05*9.81-(.05+.1235).563)/(.1235*9.81)

And I get roughly .324 for the coefficient.

Now if I were to add some mass, that shouldn't change the coefficient should it?

Another set of data we took was m1=.1kg, m2=.2235kg, a=.911m/s^2

Plugging into the same equation I get roughly .313 for the coefficient.

Is there something that was done wrong? I would have assumed that the coefficient would stay the same for each run but this equation is giving me different answers. What is going on? Thank you.

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# Homework Help: Help with varying coefficients of friction

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