Pi in the Sky Lab
Name: ________________________
Materials: rubber stopper attached to a weight through a plastic tube with fishing line, paper clip, stopwatch,
goggles, scale, meter-stick
Question: How does the radius of the circle affect the tangential (linear) velocity?
Procedure:
1. Get the mass of the rubber stopper. _________ g = _________ kg
2. Get the mass of the “weight” on the bottom of the string. ________ g = ________ kg = ________N
3. Measure the distance from the rubber stopper to the plastic tube. Record in data table. Tube should touch the
paper clip.
*****Put on goggles*****
4. Hold tube vertically and carefully spin rubber stopper to get a consistent/stable “orbit” .
Note: Start with a small circle and then increase radius by allowing weight to climb closer to the tube.
5. Time 10 revolutions (periods). Repeat 2 more times.
6. Find average time for 10 revolutions.
7. Divide by 10 to calculate the Time for 1 Rotation.
8. Increase the radius and repeat steps #3-7.
9. Calculate the Tangential Velocity, Centripetal Acceleration, and Centripetal Force.
Data:
Radius
(m)
Trial 1
(sec)
Trial 2
(sec)
Trial 3
(sec)
Average of
Trials 1-3
(sec)
Time for 1
Rotation
(sec)
Linear
aC (m/s2)
Velocity
(m/s)
FC (N)
Conclusion Questions:
1. What causes the centripetal force in this lab? (Hint: It is NOT the string.)
2. How does increasing the radius affect tangential (linear) velocity ?
3. If the weight at the bottom of the string increases, what two variables could change (and describe how they
change) to keep the rubber stopper spinning in a stable manner?