Experiment
Conservation of
Angular Momentum
14
INTRODUCTION
In your study of linear momentum, you learned that, in the absence of an unbalanced external force,
the momentum of a system remains constant. In this experiment, you will examine how the angular
momentum of a rotating system responds to changes in the moment of inertia, I.
OBJECTIVES
In this experiment, you will




Collect angle vs. time and angular velocity vs. time data for rotating systems.
Analyze the -t and -t graphs both before and after changes in the moment of inertia.
Determine the effect of changes in the moment of inertia on the angular momentum of the
system.
Find the moment of inertia of an oddly shaped object.
MATERIALS
Vernier data-collection interface
Logger Pro or LabQuest App
Vernier Rotary Motion Sensor
Vernier Rotary Motion Accessory Kit
ring stand
balance
metric ruler
PRE-LAB
1. Mount the Rotary Motion Sensor to the ring stand. Place the 3-step Pulley on the rotating shaft of
the sensor so that the largest pulley is on top. Measure the mass and diameter of the aluminum
disk with the smaller hole. Mount this disk to the pulley using the longer machine screw and
sleeve (see Figure 1).
Figure 1
2. Connect the sensor and open Logger Pro. The default data-collections settings are appropriate for
this experiment.
Advanced Physics with Vernier – Mechanics
©Vernier Software & Technology
14 - 1
Experiment 14
3. (1 point) Spin the aluminum disk so that it is rotating reasonably rapidly, then click “Collect.”
Note that the angular velocity gradually decreases during the interval in which you collected data.
What is causing the rotation of the disk to slow down?
4. (3 points) From your graph, gather the information required below and calculate the angular
acceleration.
o =
f =
t=
5. (2 points) Now determine acceleration on Logger Pro by obtaining the slope of the -t graph.
Compare this number with your calculated number above.
 = _____________________
PROCEDURE
1. Obtain the second aluminum disk from the accessory kit; determine its
mass and diameter. Position this disk (cork pads down) over the sleeve
of the screw holding the first disk to the pulley. Practice dropping the
second disk onto the first so as to minimize any torque you might apply
to the system (see Figure 2).
2. Begin the first disk rotating rapidly and begin collecting data. After a
few seconds, drop the second disk onto the rotating disk and observe the
change in both the -t and -t graphs. Record the angular velocity the
moment before the “collision” and the moment after.
3. Now pull out the steel disk and its mass. Measure and
record the diameter of both the central hole and the entire
disk. Replace the first aluminum disk with the steel disk
(and hub) and tighten the screw as before (see Figure 3).
Figure 2
4. Repeat the experiment, dropping the aluminum disk onto the steel disk after a
few seconds. Record the angular velocity the moment before the “collision” and the
moment after.
Figure 3
5. Now get a blob of clay. Decide which disk you want initially mounted. Get it
spinning (not so fast that the blob is thrown—we want it to stay on the disk), press
collect, wait a few seconds and drop the blob onto the disk. Record the angular
velocity the moment before the “collision” and the moment after.
Conservation of Angular Momentum
DATA TABLES (17 points)
Aluminum Disk with small hole:
Aluminum Disk with large hole and cork pads:
Mass = __________________
Mass = __________________
Diameter = _______________
Diameter = _______________
Radius = _________________
Radius = _________________
Steel Disk with hub: 𝑰 =
𝟏
𝟐
(𝒓𝟐𝒐 + 𝒓𝟐𝒊 )
Mass = _______________________
Inner diameter = ________________
Inner radius (rf) = ____________
Outer diameter = _______________
Outer radius (ro) = ___________
o (rad/s)
f (rad/s)
2 Aluminum disk collision
Steel/aluminum disk collision
_____________ disk/blob of
(type of disk)
clay collision
EVALUATION OF DATA
1. (6 points) Calculate the moments of inertia of the 3 disks (show work):
Experiment 14
2. (6 points) For the first 2 collisions (disk collisions), determine the total angular momentum before
the collision (show work).
Aluminum-Aluminum (before)
Steel-Aluminum (before)
3. (6 points) For the first 2 collisions, determine the total angular momentum after the collision
(show work).
Aluminum-Aluminum (after)
Steel-Aluminum (after)
4. (4 points) How well do your results show conservation of angular momentum? Determine the
difference from before to after for each collision.
Aluminum-Aluminum
Steel-Aluminum
5. (4 points) Use conservation of angular momentum to determine the moment of inertia of your
clay blob. (Show all work.)
6. (5 points) In this experiment, the moment of inertia of the rotating system was changed by adding
mass. In what other way could one change the moment of inertia? Describe an example of how this
could be done. Explain specifically how this changes I and then produces a change in  .
Conservation of Angular Momentum
AP Physics
Conservation of Angular Momentum Lab
PRE-LAB
3. (1 point) Spin the aluminum disk so that it is rotating reasonably rapidly, then click “Collect.”
Note that the angular velocity gradually decreases during the interval in which you collected data.
What is causing the rotation of the disk to slow down?
4. (3 points) From your graph, gather the information required below and calculate the angular
acceleration.
o =
f =
t=
5. (2 points) Now determine acceleration on Logger Pro by obtaining the slope of the -t graph.
Compare this number with your calculated number above.
 = _____________________
Experiment 14
DATA TABLES (17 points)
Aluminum Disk with small hole:
Aluminum Disk with large hole and cork pads:
Mass = __________________
Mass = __________________
Diameter = _______________
Diameter = _______________
Radius = _________________
Radius = _________________
Steel Disk with hub: 𝑰 =
𝟏
𝟐
(𝒓𝟐𝒐 + 𝒓𝟐𝒊 )
Mass = _______________________
Inner diameter = ________________
Inner radius (rf) = ____________
Outer diameter = _______________
Outer radius (ro) = ___________
o (rad/s)
f (rad/s)
2 Aluminum disk collision
Steel/aluminum disk collision
_____________ disk/blob of
(type of disk)
clay collision
EVALUATION OF DATA
1. (6 points) Calculate the moments of inertia of the 3 disks (show work):
Conservation of Angular Momentum
2. (6 points) For the first 2 collisions (disk collisions), determine the total angular momentum before
the collision (show work).
Aluminum-Aluminum (before)
Steel-Aluminum (before)
3. (6 points) For the first 2 collisions, determine the total angular momentum after the collision
(show work).
Aluminum-Aluminum (after)
Steel-Aluminum (after)
4. (4 points) How well do your results show conservation of angular momentum? Determine the
difference from before to after for each collision.
Aluminum-Aluminum
Steel-Aluminum
5. (4 points) Use conservation of angular momentum to determine the moment of inertia of your
clay blob. (Show all work.)
6. (5 points) In this experiment, the moment of inertia of the rotating system was changed by adding
mass. In what other way could one change the moment of inertia? Describe an example of how this
could be done. Explain specifically how this changes I and then produces a change in  .