Lab Activity Phys221:
Circular Motion
Objective: In this lab activity you will conduct a number of experiments that involve
circular motion (uniform or non-uniform) and analyze them in terms of forces and
accelerations.
Part 1: Measuring a coefficient of friction
A. Given the rotating apparatus, come up with a procedure to measure the coefficient of
friction between a penny and the ruler. Ask me for anything than you think you will
need (Hint: e.g. a stopwatch). Of course, your procedure must somehow include the
rotation of the ruler. Will you measure static or kinetic friction?
B. Do the experiment and take measurements.
C. Find the coefficient of friction from your measurements.
D. There are other ways to find the coefficient of friction between a penny and the ruler.
Find another such way (Hint: you could use the ruler as an incline). Do you get the
same answer?
Part 2: Why does the water stay in the bucket?
A. Imagine swinging a bucket of water over your head. How fast should you swing the
bucket to keep the water in the bucket? Make a prediction.
B. Do the experiment. Instead of water, put a tennis ball in the bucket (…unless you
really trust your prediction). Take measurements.
C. Conclusion: how well did the experiment match your prediction?
Part 3: Rolling friction up and down
You are provided with x-t, and v-t graphs for a cart that is given a push up an incline
(similar to what you did at the beginning of the quarter). The cart slows to a stop, reverses
direction, and then rolls back downhill. You will use this data to find the coefficient of
rolling friction  between the cart and the incline and the angle of the incline.
Follow the steps outlined below in the report section.
Lab Activity Phys221:
Circular Motion
Report:
This is a group write up. It must be word-processed. All graphs must be integrated into
the text (not attached at the end).
Part 1:
1. Describe the purpose of your experiment.
2. Describe the procedure. What did you measure? How did you take your
measurements?
3. Present your data in a table.
4. Include two FBDs, one for each method.
5. Include a clear theoretical calculation of what you have measured. For part 1, show
how the coefficient of friction can be derived from your measurements.
6. Do problem 8.34 at the end of the chapter. Turn this in with your report.
Part 2:
1. Do problem 8.17 at the end of chapter 8.
Part 3:
1. Use LoggerPro to find the acceleration of the cart as it moves uphill (aup). Include a
graph of the data that shows your best fit results. Use the v-t graph for this. Indicate in
your graph the best fit and the part of the motion you used.
2. Use LoggerPro to find the acceleration of the cart as it moves downhill (adown). Include
a graph of the data that shows your best fit results. Use the v-t graph for this. Indicate in
your graph the best fit and the part of the motion you used.
3. Draw a FBD for the cart as it moves uphill. Include a coord. system.
4. Use Newton’s 2nd law (  Fx  max ,  Fy  ma y ) to show that the equation for aup
should be: aup  g sin    g cos  (eq1)
5. Draw a FBD for the cart as it moves downhill. Include a coord. system.
6. Use Newton’s 2nd law (  Fx  max ,  Fy  ma y ) to show that the equation for adown
should be: adown  g sin    g cos  (eq2)
7. What would the acceleration of the cart be if there were NO friction?
8. Compare your acceleration aup and adown to the acceleration without friction. Do your
results make sense?
9. Add equations (eq1) and (eq2) to eliminate  and solve for .
10. Find and 
11. The angle of the incline should be a little greater than 9 degrees. Compare this to your
result.