I am doing a lab about static and kinetic friction. We had a block on a surface
ID: 2138459 • Letter: I
Question
I am doing a lab about static and kinetic friction. We had a block on a surface connected to a string of which we changed the weight. At the end of the string was a cup of sand hanging off the table that we continuously added sand to until the block began to accelerate. I was asked to plot the force applied by the sand versus the force exerted on the track by the block and its load for both the kinetic and static cases. I assumed that for each of these forces I would just times the mass of each by gravity. I plotted those forces and got the graph below. Now I am being asked to find the coefficients of friction for the block in all of the cases. I need help figuring out the coefficient of friction and please write out how you do it. I have listed my data below. Also, let me know if I have created the wrong graph!
static case
mass of block
165.5 g
265.5
365.5
465.5
665.5
mass of sand
65.6 g
98.2
145
171.5
231
kinetic case
block masses are same as before
sand mass:
59 g
91.1
125.6
162.8
224.3
Explanation / Answer
F= u*N
N=Mb *g
F=Ms*g
u= Ms/Mb
divide the mass of sand by mass of block to obtain the coefficient of friction:
static:
0.396 (65.6/165.5), 0.369 (98.2/265.5)...etc and finally avergae all thse 5 values to find the static friction factor.
kinematic:
0.356 (59/165.5), 0.343 (91.1/265.5) etc and finally avergae all thse 5 values to find the static friction factor.
Your graph is right. Kinetic friction factor should be less than static.
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