Coefficient of Friction
Physics 111 Lab
Let’s pretend you work for the Acme Toy Company. Because of a lawsuit brought against your company, your boss needs to know the maximum coefficient of static friction between their standard toy ramp and various objects. Your assignment is to measure µs maxbetween the ramp and one of these objects.
You will measure µs max by putting your object on the ramp and lifting up one end of the ramp and seeing what the maximum angle the ramp can be before your object slips. Measure this angle and whatever other thing(s) you need to measure several times as accurately and precisely as possible (your job and the awesome benefits that come with it might depend on this!). Each set of measurements will give you a value of µs max. Take the average of these µs max’s as your value for µs max and the standard deviation as the uncertainty in your measurement of µs max. Your “boss” (Richard) will supply you with the object, but the ramp used can be found at the south end of the room.
The usual report is required:
Name/Partners/Date/Title (0.4 pts)
Introduction (0.2 pts) – State the purpose of the experiment. Be specific about the two objects you are measuring µs max between.
Theory (1.2 pts) –Start with a free-body diagram and derive an expression for µs max in terms of the things you will be measuring. Don’t forget to define your variables! (Here, your expression may come out surprisingly simple.)
Experiment (1.4 pts) – Describe what you are doing, and include a diagram. You need to include enough procedure/information here to convince the court and jury that you did things correctly (they will not see this handout). Measure each thing you need to measure several times. Include ALL of your measurements here. Precision and accuracy count!
Analysis (1.0 pts) – Crunch your numbers. For each set of measurements, determine a value of µs max. Determine the average and standard deviation of these values of µs max.
Discussion (0.6 pts) – Is this a reasonable result? Why or why not? Convince the court and jury! You can compare your value to those measured by those around you (things with more friction should have larger µs max’s). If it is not reasonable, go back and check your work! If you made a mistake, go back and fix it, retaking data if necessary. Don’t turn in flawed results. Note that it is possible to have µs max > 1, but this is rare. If yours comes out bigger than 1, it is a good idea to go back and check things, but it isn’t impossible.
Conclusion (0.2 pts) – Repeat your measurement of µs max and its uncertainty.
Dr. Richard A. Thomas – UST Physics