# friction between two surfaces

by jamesyboy1990
Tags: friction, surfaces
 P: 16 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
 PF Patron Sci Advisor Emeritus P: 9,789 How did you calculate the coefficient of friction for your results?
 P: 16 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)
PF Patron
Emeritus
P: 9,789

## friction between two surfaces

And how did you calculate the normal reaction force?
 P: 16 R = mg cosx F = mg sinx so in essence, the coefficient was tanx
 P: 16 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)
 PF Patron Sci Advisor Emeritus P: 9,789 Your not actually plotting $\mu$ vs. $m$ what your actually plotting is $\tan\theta$ vs. m since; $$\mu = \frac{F}{R} = \frac{mg\sin\theta}{mg\cos\theta} = \tan\theta$$
 P: 16 but since tanx = u, so why should it matter whether you plot u vs. m or tanx vs m?
PF Patron
Indeed, $\tan\theta = \mu$, but are you keeping the angle constant?