PHYS 2425 – Engineering Physics I
Impulse and Momentum
Leader: ____________________ Reporter: ___________________________
Skeptic: ___________________ Encourager: _________________________
Materials
Pasco Dynamics Track Laptop
Cart with force probe attached Labpro
Motion Detector Force Probe
Rubber Band
Introduction
In this lab, we will investigate the relationship between impulse and momentum.
Preliminaries
Answer the following questions in your group before proceeding with the lab activity.
In this lab you will aim tug a dynamics cart with an attached force sensor
1. If the cart is initially at rest, sketch a graph of what you think the velocity versus time graph will look like for this experiment.
2. Sketch a graph of what you think the force versus time will look like.
3. If the initial velocity of the cart is increased, what do you think will be the affect on your answers to questions 1 and 2?
4. If instead you push briefly
on the force probe with the cart initially at rest towards the motion detector,
sketch graphs of what you think the Velocity vs. Time and the Force vs. Time
will look like.
Procedure
In this experiment we will use a force probe attached to a dynamics cart and a motion detector. We will pull the cart, with a rubber band attached to the force probe and record the force as we pull on it. We will simultaneously record the velocity of the cart using the motion detector.
1. Set up
Determine the mass of the cart along with the force probe. Plug the force sensor into CH 1 on the LabPro and the Motion Detector into DIG/SONIC 1. Position the sensors so that the tip of the force sensor faces away from the motion detector. Make sure that the switch on the force probe is in the +/- 10 N position. The motion detector needs to be at least .5 m from the cart. Start LoggerPro and double click on the folder titled “_Physics with Computers” and then open the file “20 Impulse and Momentum”. Click OK on the Confirm Sensors box if it opens.
2. Data Collection and Analysis
Part 1 - Tugging a cart at rest away form the motion detector
Click on the 0 button 
(should be next
to the collect button) and then click OK on the box that opens to zero the
force probe. Click on the collect button and once you hear the motion detector
steadily clicking, use the rubber band to give the cart a brief horizontal tug away
from the motion detector. You should obtain a brief impulsive force and a
velocity graph with two plateaus. Check with your instructor to make sure you
have good data.
Before and after the tug,
the cart should have had a constant velocity. On the velocity versus time
graph, click and drag over the part of the graph which indicates the constant
velocity before the tug. Click on the button which says STAT 
, and record the mean value
of the initial velocity. Repeat this step for the velocity of the cart after
the tug. To analyze our data we will calculate a quantity called momentum.
Momentum which is denoted by the letter p is defined as p = mass x velocity or p = mv.
Q1. Complete the following table.
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Mass |
Velocity |
Momentum = mass x velocity |
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Initial |
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Final |
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Q2. Determine the change in momentum of the cart. Be sure to include units.
Click on the Force vs. Time
graph, and then click and drag over the impulse. Click on the button which
shows a graph with a shaded area underneath it, 
. This will calculate the area of
the region that you indicated which is the impulse.
Q3. Record the impulse I =
Q4. What is the sign of the impulse? In terms of the motion of the cart, why does the impulse have that sign?
Q5. What are the units of the impulse given by the computer? Show that these are the same as the units of momentum.
Q6. Calculate the percent difference between the impulse and the change in momentum using the following formula
% difference = 
Part 2 - Pulling harder on a cart initially at rest away from the motion detector
P7. If you give the force probe a sharper tug, how do you think the impulse will change?
Q8. Test your answer to P7 by running the experiment again with a sharper tug on the cart greater than the previous run. Record your data in the space below.
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Mass |
Velocity |
Momentum |
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Initial |
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Final |
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Q9. Determine the change in momentum of the cart. Be sure to include units.
Q10. Record the impulse: I =
Q11. Determine the % difference
Part 3 - Pulling away from the motion detector on a cart initially moving towards the motion detector
P12. Now, if the cart initially moves towards the motion detector, and you pull away, sketch predictions of what the graphs of Force vs. time and velocity vs. time will look like.
Q13. Test your answer to P12 by running the experiment again with the cart initially moving towards the motion detector and then giving a brief tug in the opposite direction.
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Mass |
Velocity |
Momentum |
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Initial |
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Final |
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Q14. Determine the change in momentum of the cart. Be sure to include units.
Q15. Record the impulse: I =
Q16. Determine the % difference
Part 4 - Pushing a cart initially at rest towards the motion detector
P17. If the cart is initially at rest and you push the cart towards the motion detector, sketch predictions of what the graphs of Force vs. time and velocity vs. time will look like.
Q18. Test your answer to P17 by running the experiment again. This time place the cart at rest at the end of the track opposite the motion detector and briefly push the cart towards the motion detector by pushing on the tip of the force probe. Don’t allow the cart to run into the motion detector.
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Mass |
Velocity |
Momentum |
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Initial |
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Final |
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Q19. Determine the change in momentum of the cart. Be sure to include units.
Q20. Record the impulse: I =
Q21. Determine the % difference
Summary
I. On the graphs below, sketch the general shape of the impulse and the corresponding change in velocity that you observed in parts 1-3 of this experiment.
II. On the graphs below, sketch the general shape of the impulse and the corresponding change in velocity that you observed in part 4of this experiment.
III. For the impulse shown, sketch a graph of a possible change in velocity.
IV. For the indicated change in velocity, sketch a graph of the impulse.
