AP Physics
Impulse and Momentum
OBJECTIVES
In this experiment, you will
 Collect force, velocity, and time data as a cart experiences different types of collisions.
 Determine an expression for the change in momentum, p, in terms of the force and duration
of a collision.
MATERIALS
Vernier data-collection interface
Logger Pro
Vernier Photogate
Vernier Dual-Range Force Sensor
Motion Track
standard cart
Cart Picket Fence
Hoop bumper
Clay
PRE-LAB QUESTION
1. (3 points) In a car collision, the driver’s body must change speed from a high value to zero. This
is true whether or not an airbag is used, so why use an airbag? How does it reduce injuries?
PROCEDURE
1. Use clay or tape to hold the picket fence standing up in the cart. (I would put the edge with the
big black rectangle up. (See Picture.)
2. Set up a Photogate so that when you push the car, the picket fence will go nicely through the
photogate and only read the top black rectangle. You also need it located far enough away from
the edge of the track where the collision will occur so that the picket fence will pass entirely
through the photogate before the collision.
3. Adjust the leveling screws on the feet as needed to level the track.
4. Unscrew the hook from the force sensor (don’t lose it, please, and return it when the lab is
finished!). Replace it with the hoop. Set the force sensor on the track, resting against the bumper
where you intend the collision to take place.
5. Plug the force sensor and the photogate into the interface. We will use the graphs that are
automatically generated. There is NOT a pre-programmed lab for this experiment. The force
Advanced Physics with Vernier – Mechanics
©Vernier Software & Technology
10B - 1
sensor should generate a force vs. time graph. The photogate will generate more than 1 graph.
We only need the velocity vs. time graph.
6. Set up Logger Pro data collection.
a. Click on the stopwatch icon
near the collect button. Change the data-collection rate
to 500 samples/second and the data-collection length to 5 seconds.
b. Click on the “Experiment” menu at the top. Choose Set Up Sensors ►Show All
Interfaces.
c. Click the image of the Photogate and choose Gate Timing. You will see the position and
acceleration graphs disappear and leave the velocity graph and a Gate Time graph. We
will not be using the Gate Time graph. I would delete it to have room.
Make the necessary adjustments so that two graphs, force vs. time and velocity vs. time, appear
in the graph window. (Do NOT delete the data table box. We will use it!)
Part 1 Bouncy collision
1. Practice launching the cart with your finger so that when it collides with the hoop bumper, it
slows to a stop and reverses direction smoothly. Do not push the cart so hard that the hoop
compresses fully and the cart hits the force sensor!
2. Zero the force sensor.
3. Click on Collect, then launch the cart toward the hoop spring bumper.
4. Record the mass of the cart (plus all the stuff on the top of it) in the data table. To determine your
initial and final velocities, click on the data tables on the left hand side. Use the bottom scroll bar
to scroll over until you see the velocity column. Your velocities should be listed there. Keep in
mind that one of these velocities is negative!
5. On the force vs. time graph, we want to gather data about impulse. Recall that 𝐽 = ∫ 𝐹𝑑𝑡 which
means that we can use the area under the curve to determine impulse. Figure out how to zoom in
on the area of the collision. Use your mouse to highlight only the section of the
collision. Then use the integral button
to determine the area under the curve. Enter this
value for measured impulse in the data table.
Part 2 Sticky collision
1. Unscrew the hoop bumper. Screw the clay holder bumper (looks like a washer on a screw) into
the force sensor. Try to mold the clay into a cone shape that is attached only to the clay holder.
(Don’t let it touch the plastic molding of the force sensor, otherwise force will be measured
incorrectly.) Attach another piece of clay to the cart so that the two pieces of clay will come in
contact with each other during the collision and make the cart come to a complete stop. (It may
be necessary to reattach the hook and mold the clay around it to hold the clay in place. Just make
sure there is a good amount of clay sticking out so that the car will not actually touch the hook
during the collision.)
2. Practice launching the cart with your finger so that when the clay “nose” on the front of the cart
collides with the clay on the force sensor, the cart comes to a stop without bouncing. A collision
that is too jarring will not yield satisfactory data.
3. Reshape the clay and re-zero the force sensor. Click on Collect, then gently launch the cart
through the photogate.
4. Collect data as before.
DATA TABLE
Mass (kg)
Initial
Velocity
(m/s)
Final Velocity
(m/s)
Change in
Momentum
(kg∙m/s)
Impulse
(kg∙m/s)
Bouncy
Collision
Sticky
Collision
EVALUATION OF DATA
Part 1 Bouncy collision
1. Keeping in mind that one of the velocities is negative, calculate the change in momentum, Δp,
from your data. Enter this value in the data table.
2. Determine the % difference between the change in momentum and the impulse using the
following formula:
𝐻𝑖𝑔ℎ 𝑣𝑎𝑙𝑢𝑒−𝑙𝑜𝑤 𝑣𝑎𝑙𝑢𝑒
𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑜𝑓 𝑡ℎ𝑒 2 𝑣𝑎𝑙𝑢𝑒𝑠
5. Meet with other lab groups to compare your findings to those of others in your class.
Lab Group Names
% difference calculation
6. What can you conclude about the relationship between change in momentum and impulse in this
type of collision?
Part 2 Sticky collision
1. Assuming the final velocity is zero, determine the change in momentum, p, of the cart. Enter
this value in your data table.
3. Some “bouncing” is unavoidable. You may see some actual oscillations near the “end” of the
collision on the force vs. time graph when you zoom in. Explain how you selected an
“appropriate interval” of the F-t graph for your determination of the impulse.
4. As you did with the bouncy collision, determine the % difference between the impulse and the
change in momentum.
5. Meet with other lab groups to compare your findings to those of others in your class.
Lab Group Names
% difference calculation
6. What can you conclude about the relationship between change in momentum and impulse for this
type of collision? How does this relate to your findings for the bouncy collision?
7. From Newton’s second law (F = ma), derive the equation you have determined from the analysis
of your data.
EXTENSIONS
1. When you catch a fast-moving baseball, it hurts less when your hand “gives” a little than if you
hold your hand stiff. Explain why in terms of impulse and change in momentum.
2. Now cars are made to crumple during a collision. Explain in terms of impulse and change in
momentum why car manufacturers are doing this.
AP Physics
Impulse Lab
PRE-LAB QUESTION
1. (3 points) In a car collision, the driver’s body must change speed from a high value to zero. This
is true whether or not an airbag is used, so why use an airbag? How does it reduce injuries?
DATA TABLE (8 points)
Mass (kg)
Initial
Velocity
(m/s)
Final Velocity
(m/s)
Change in
Momentum
(kg∙m/s)
Impulse
(kg∙m/s)
Bouncy
Collision
Sticky
Collision
EVALUATION OF DATA
Part 1 Bouncy collision
1. Keeping in mind that one of these velocities is negative, calculate the change in momentum, Δp,
from your data. Enter this value in the data table.
2. (2 points) Determine the % difference between the change in momentum and the impulse using
the following formula:
𝐻𝑖𝑔ℎ 𝑣𝑎𝑙𝑢𝑒−𝑙𝑜𝑤 𝑣𝑎𝑙𝑢𝑒
𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑜𝑓 𝑡ℎ𝑒 2 𝑣𝑎𝑙𝑢𝑒𝑠
5. (5 points) Meet with other lab groups to compare your findings to those of others in your class.
Enter their values in the table below.
Lab Group Names
% difference calculation
6. (2 points) By analyzing the values in the table, what can you conclude about the relationship
between change in momentum and impulse in this type of collision?
Part 2 Sticky collision
1. Assuming the final velocity is zero, determine the change in momentum, p, of the cart. Enter
this value in your data table.
3. (2 points) Some “bouncing” is unavoidable. You may see some actual oscillations near the “end”
of the collision on the force vs. time graph when you zoom in. Explain how you selected an
“appropriate interval” of the F-t graph for your determination of the impulse.
4. (2 points) As you did with the bouncy collision, determine the % difference between the impulse
and the change in momentum.
5. (5 points) Meet with other lab groups to compare your findings to those of others in your class.
Lab Group Names
% difference calculation
6. (4 points) What can you conclude about the relationship between change in momentum and
impulse for this type of collision? How does this relate to your findings for the bouncy collision?
7. (3 points) Compare your results between the bouncy collision and the sticky collision. Which
showed a greater change in momentum (impulse)? Is this what you expected? Explain.
8. (4 points) From Newton’s second law (F = ma), derive the equation you have determined from
the analysis of your data.
EXTENSIONS
1. (5 points) When you catch a fast-moving baseball, it hurts less when your hand “gives” a little
than if you hold your hand stiff. Explain why in terms of impulse and change in momentum.
2. (5 points) Now cars are made to crumple during a collision. Explain in terms of impulse and
change in momentum why car manufacturers are doing this.