Conservation of Angular Momentum Lab – PHY 161
Introduction: Measure the angular velocity of a spinning disk; then drop another
disk and measure the final angular velocity. Test predictions based on conservation
of angular momentum during the collision.
1. Is the final angular velocity in agreement with the theoretical prediction?
2. Is the angular momentum conserved?
Data: Table and Graph (Lf vs. Li).
Analysis:
1. Show M1, D1 and I1, the mass, diameter and moment of inertia of disk 1. Do
the same for disk 2.
2. Pick the worst-performing case, the one with greatest disagreement between
experiment and theory. Show i,exp and %unc(i,exp), f,exp and %unc(f,exp),
f,theo and %unc(f,theo), and %Diff(f,exp, f,theo). Is the theoretical prediction
correct? Show the ratio Lf/Li. Is angular momentum conserved?
3. Show the slope and y-intercept for the graph. What is the theoretical
prediction for the slope and y-intercept?
Conclusion: Provide final answers to the questions presented in the Introduction.
I.e., overall, was the theoretical prediction for f close to the measured value?
Overall, was angular momentum conserved? It is not necessary to quote again the
numbers from the Analysis. However, do provide your best explanation for the lack
of agreement between theory and experiment, if any such disagreement exists.
Additional questions: Answer questions 1-2 from the Lab Instructions, reproduced
here for convenience:
1. In this experiment, the presence of friction was not taken into consideration.
How would the presence of friction affect the experiment? Is the angular
moment still conserved? Is this a source of random or systematic error? Why?
2. The pads on disk 2 are to prevent slipping during collisions. Assuming that the
axle is truly frictionless, will the final angular speed (at which disk 1 and disk 2
ultimately rotate together) be different if disk 2 did not have those pads? Why?