AP Physics Lab 2x09: Conservation of (Linear) Momentum
EQUIPMENT NEEDED
Science Workshop™ Interface
Smart Pulley (two)
Collision track
Collision cart (two)
Assorted masses
Balance (for measuring mass)
String
Paper Clips
PURPOSE
The purpose of this laboratory activity is to investigate the momentum of two carts before and after an
elastic collision.
THEORY
Momentum is conserved during collisions. The momentum of an object is the product of its mass and its
velocity. By the law of Conservation of Momentum, the sum of the momentums in a system prior to a
collision (or other interaction) equals the sum of the momentums in the system after the collision.
If external forces such as friction are ignored, the sum of the momentums of the two carts prior to a collision
is the same as the sum of the momentums of the carts after the collision.
PROCEDURE
For this activity, Smart Pullies will measure the motion of two carts during an “explosion.” The Data Studio
program calculates velocity for both carts. A graph of the motion for both carts reveals their momenta
before and after the collision.
PART I: Equipment Setup
1. Set up the equipment as shown in the diagram below. The pulleys shown are Smart Pulleys.
2. Adjust location and height so the connecting string is horizontal and aligned along the center axis of
the track.
3. Use the balance and assorted masses to bring both carts to equal mass. Record the mass.
4. Place small masses on the hanging end of the connecting string to counterbalance the carts’ friction.
5. Set “Start Condition” to be Location > 10 cm for the cart that will move quickest.
6. Since various collisions will be investigated, it is suggested that the “Stop Condition” be left as
manual.
7. Create a velocity vs time graph (with “locked” X-axis) to show the input from both sensors.
AP_L_2x09 Conservation of Momentum
PART II: Data Recording; “Explosion” w/ Equal Masses
1. Orient the carts so that the plunger will push them apart when activated.
2. Start Data Studio, release the carts, and stop Data Studio before the carts run off the end of the
track.
3. Repeat Steps 1&2 until you have a good run for each team member (and a spare).
4. Analyze the data as required to show Conservation of Momentum. An optional Data Table is
provided for your use.
5. Calculate R%E (|difference| compared to the |average| ) for your trial.
PART III: Data Recording; “Explosion” w/ Unequal Masses
1. Add some mass to one of the carts to create unequal masses.
2. Repeat Part II.
PART IV: Data Recording; “Blamming”
1. Place one cart in the middle of the track and the other at the end of the track. Orient the carts so
the velcro tabs will cause the carts to stick together when they collide.
2. Start Data Studio, gently push the cart at the end of the track toward the center cart so that they
collide and stick together. Stop Data Studio before the carts run off the end of the track.
3. Repeat Steps 1&2 until you have a good run for each team member (and a spare).
4. Analyze the data as required to show Conservation of Momentum. An optional Data Table is
provided for your use.
5. Calculate R%E (|difference| compared to the |average| ) for your trial.
PART V: Data Recording; “Bouncing”
1. Place one cart in the middle of the track and the other at the end of the track. Orient the carts so
the embedded magnets are aimed at each other.
2. Start Data Studio, gently push the cart at the end of the track toward the center cart so that their
magnetic fields bounce off each other. Stop Data Studio before the carts run off the end of the
track.
3. Repeat Steps 1&2 until you have a good run for each team member (and a spare).
4. Analyze the data as required to show Conservation of Momentum. An optional Data Table is
provided for your use.
5. Calculate R%E (|difference| compared to the |average| ) for your trial.
ANALYSIS (Attach typed and organized responses; use the Cover Page provided.)
1. Create a summary table showing (only) the momenta before and after the incident for each trial.
Include the R%E for each trial.
2. Were all trials within accepted R%E? If not, offer “directed suggestions” as to why not.
3. What factors may cause there to be a difference between momentum before and momentum after the
incident. Be specific and explain (directionally) how each factor would influence the experiment.
4. Why was only one Smart Pulley needed for part IV?
5. Explain the visual characteristics that determine when data should be taken from the graphs for each
part.
6. Attach all graphs (annotated) used for data analysis (showing the specific data collected).
7. What is the name of the *.ds file this lab’s data is stored in? (Your Data Studio file should be available
upon request.)
8. Attach data tables.
9. Attach Journal pages.
AP_L_2x09 Conservation of Momentum
Regents Count: 2
DATA TABLE: Part II
Cart #1
Cart #2
0 m/s
0 m/s
Σp
mass (kg)
vbefore (m/s)
mvbefore (kg m/s)
vafter (m/s)
mvafter (kg m/s)
R%E
DATA TABLE: Part III
Cart #1
Cart #2
0 m/s
0 m/s
Σp
mass (kg)
vbefore (m/s)
mvbefore (kg m/s)
vafter (m/s)
mvafter (kg m/s)
R%E
AP_L_2x09 Conservation of Momentum
DATA TABLE: Part IV
Cart(s)
m before (kg)
vbefore (m/s)
mvbefore (kg m/s)
m after (kg)
vafter (m/s)
mvafter (kg m/s)
R%E
DATA TABLE: Part V
Cart #1
Σp
Cart #2
mass (kg)
vbefore (m/s)
mvbefore (kg m/s)
vafter (m/s)
mass (kg)
mvafter (kg m/s)
R%E
AP_L_2x09 Conservation of Momentum
Regents Count: 2