Unformatted text preview: EXPERIMENT 7. FRICTION
10. Repeat the above procedure testing diﬀerent surfaces of the block: the large and small
wooden surfaces and the large felt surface in contact with the paper for one set of
Enter your data into excel. Using a separate worksheet for each block surface, labeled
appropriately, complete the following analysis
1. Plot the average force of static friction and the average force of kinetic friction versus
the normal force on the cart (both should be on the same plot). Give your plot an
appropriate title, axes labels indicating units and any other formatting necessary for
it to be easily understood.
2. Fit a line to the data using the “add trendline” option. Record the slope of the line this is the value of the coeﬃcient of friction for the particular type of friction (static
or kinetic) being plotted.
3. From your uncertainty in the force of friction with the cart fully loaded, estimate
the uncertainty in the coeﬃcient of friction from δµ ≈ mg (note this neglects the
uncertainty in the mass because the total uncertainty will be dominated by δf )
4. Print out your graphs and record on each the measured coeﬃcients of kinetic and static
friction, along with their associated uncertainty.
5. Do your measured values for µs between the large and small wood surfaces on the table
agree with each other within the experimental uncertainty? Do they diﬀer from the
coeﬃcient of static friction observed in the experiments with the felt surfaces? Which
surface had the higher value for the coeﬃcient of static friction?
6. Was the measured value of the coeﬃcient of kinetic friction less than that of static
friction for each surface being considered? If not postulate a reason why it wasn’t. 48 ...
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