Centripetal Force Lab (AP)
Initial Planning Sheet
Each person need to fill out an initial planning sheet. The sections with an asterisk (*) need to be checked by Mrs.
Wright before starting the lab.
Purpose:
The purpose of this lab is to investigate what variables effect the velocity of an object in uniform
circular motion and how.
Vocabulary:
 Radius of circular motion (r): The horizontal distance measured from the top of the tube to the
center of mass of the rubber stopper when the stopper is swinging in a circle. Radius must be
measured in meters. The center of mass of a uniform object (like the rubber stopper is in the
center)
 Period (T): The time in second for the satellite (rubber stopper or ball) to do one complete circle.
Centripetal Force (Fc): The force causing the satellite to travel around in a circle. In this case, the
satellite is attached to a string which has weights weighing it down on the other end. Without the
weights, there would be nothing to counteract the satellite. Therefore, the force on gravity on the
weights must be supplying the centripetal force for the satellite.
Apparatus:
How to use the apparatus correctly:
 Tension in the string, provided by the weight of
the masses hanging on the bottom should be the
only force providing the centripetal force. That
means, you need to practice whirling the stopper
in such a way that you are only touching the glass
tube and not the string.
 During each trial, the radius of the string must not
change. You need to mark the radius somehow.
One option would be to place a paper clip a
centimeter or so below the glass tube (upper clip
in the apparatus picture). Then as you swing the
stopper, make sure the upper clip stays in the
same spot. However, be careful that the upper clip
doesn’t touch the glass tube. Another method
would be to mark the string with a marker at the desired radius. Then keep that mark just at the
top of the tube.
* Pre-Lab Questions:
1. Define centripetal force.
2. What is providing the centripetal force in this lab? How would you calculate this force?
3. How far does the stopper travel when it goes all the way around in a circle once?
4. How will you calculate the linear velocity of the stopper?
* Procedure:
Your lab group needs to pick two variables to test to determine how those variables affect the velocity
of an object in circular motion.
Each person needs to fill out an initial planning sheet and have their procedures checked by Mrs.
Wright. Keep your initial planning sheet to staple to the back of your lab report.
* Part 1:
 Independent Variable:
 Dependent Variable:
 Variables held constant:
 Brief cartoon-strip drawing showing what you will do for this part:


Data table – Be sure in include the “raw” data. Raw data would be a number you took note of in
the lab, but then calculated on before being used. An example of raw data would be to the total
time for x spins or the velocity.
What will you graph?
* Part 2:
 Independent Variable:
 Dependent Variable:
 Variables held constant:
 Brief cartoon-strip drawing showing what you will do for this part:


Data table – Be sure in include the “raw” data. Raw data would be a number you took note of in
the lab, but then calculated on before being used. An example of raw data would be to the total
time for x spins or the velocity.
What will you graph?
Analysis:
See Lab Handout posted online for how to analyze your data.
Conclusion:
See Lab Handout posted online for what is needed in your conclusion.