Conservation of Momentum
Honors Physics
Research Question
After reading the lab, create your own research question and make a prediction in response to the
question you create.
Pre-Lab Discussion
This experiment demonstrates the conservation of momentum during an explosion. This is
accomplished by calculating the momentum of two carts pushing away from each other. When two
carts push away from each other and no net force exists, the total momentum of both cars is
conserved. Because the system is initially at rest, the final momentum of the two carts must be equal
in magnitude and opposite in direction so the resulting total momentum of the system is still ZERO.
Materials
2 carts
Motion Sensors
Mass Bars
Digital Balance
Dynamics track
String
Procedure
1. Measure the mass of the empty red and blue carts. Record in Table 1. Remember to convert
from grams to kilograms (divide by 1000).
2. Level the track by setting a cart on the track to see which way it rolls. Adjust the leveling feet to
raise or lower the ends until a cart placed at rest on the track will not move.
3. Add a motion sensor to each side of the track and plug them into the computer. In the class
folder, open the DataStudio file: conservation_of_momentum.ds.
4. Place the two carts against each other with the plunger of one of the carts pushed completely in
and latched in its maximum position, and the other facing the opposite direction. Tie the string
between the carts.
5. To make sure neither sensor is hit by the carts, start the carts closer to the end of the side with
the heavier mass.
6. Press start in DataStudio and push the plunger release button with a mass bar. Watch the two
carts move until the string snaps them back. If either cart reaches the motion sensor, change the
starting point of the carts and repeat this step. Look at the velocity vs. time graph for each cart
and record the highest speed value in Table 1 (it should be negative in DataStudio, but write the
absolute value).
7. Repeat steps 4 and 5 by adding or removing mass according to Table 1. Before starting a new
run, select “Delete Last Data Run” under the “Experiment” menu.
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Data Table 1
Mass of empty Blue Cart = ___________ kg
Trial
Blue Cart Mass
Added
Total
Mass
Mass
(kg)
(kg)
Red Cart Mass
Added
Total
Mass
Mass
(kg)
(kg)
1
0
0
2
0.250
0
3
0.500
0
4
0.750
0
5
1.000
0
6
0.750
0.250
7
0.500
0.250
8
0.250
0.500
9
0
0.500
10
0
0.750
Mass of empty Red Cart = ___________ kg
Table 1
Velocity
Blue
Red
Cart
Cart
(m/s)
(m/s)
Momentumexperimental
Blue Cart
(kg · m/s)
Red Cart
(kg · m/s)
Difference
(kg · m/s)
Calculations (Provide one sample calculation for each)
1. Calculate the experimental momentum of each cart, using the formula: p = mv.
2. Subtract the momentum of the red cart from the blue cart. Put in the last column above.
Questions
1. Is momentum conserved in this experiment? Explain, using actual data from the lab.
2. When carts of unequal masses push away from each other, which cart has a higher velocity?
Explain.
3. When carts of unequal masses push away from each other, which cart has more momentum?
Explain.
4. Did all of your results show conservation of momentum? Describe 3 possible sources of
error and explain specifically how they might have changed the results.