## friction between two surfaces

1. The problem statement, all variables and given/known data

hi, i am almost done my lab on the coefficient of friction on an inclined plane. I was attempting to prove that the coefficent of static friction would be the same no matter the weight of the mass that was static on the incline. However, i plotted a coefficient versus mass graph, and the line wasn't horizontal (the coefficient changed). My quick question was whether i still need to find the equation for finding the coefficient based on my results, or if i could just conclude that in my case, the coefficient didn't stay constant, and then move to my conclusion

2. Relevant equations

3. The attempt at a solution
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 Blog Entries: 1 Recognitions: Gold Member Science Advisor Staff Emeritus How did you calculate the coefficient of friction for your results?
 i had an incline, measured the weight of the mass, and changed the angle such that if i increased the angle by a little bit, the mass would slide. I did this for several different masses and recorded the angle. I then used a freebody diagram and the equation for static friciton (u = Fmax/R)

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## friction between two surfaces

And how did you calculate the normal reaction force?
 R = mg cosx F = mg sinx so in essence, the coefficient was tanx
 technically, all i need to know is whether i would have to process the graph to find a relation between weight and the coefficient (although i know that technicallly the coefficient is independant of mass) if all i wanted to prove in the lab was that the coefficient was independant of mass (and in my case, my experimental data didn't prove it)
 Blog Entries: 1 Recognitions: Gold Member Science Advisor Staff Emeritus Your not actually plotting $\mu$ vs. $m$ what your actually plotting is $\tan\theta$ vs. m since; $$\mu = \frac{F}{R} = \frac{mg\sin\theta}{mg\cos\theta} = \tan\theta$$
 but since tanx = u, so why should it matter whether you plot u vs. m or tanx vs m?

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Indeed, $\tan\theta = \mu$, but are you keeping the angle constant?