Experiment 10: Impulse and Momentum Names Type here Group # Type here

Experiment 10: Impulse and Momentum

Names

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Group #

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Date

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Experiment 10: Impulse and Momentum – online version

OVERVIEW

In this lab you will investigate the relationship between impulse and momentum, examine the forces in a one-dimensional collision, and see if momentum is conserved in one-dimensional collisions.

PROCEDURE

Activity 1: Impulse and momentum

1. Set up the simulation. Use the simulation at https://interactives.ck12.org/simulations/physics/crash-test-dummy/app/index.html?screen=sandbox&lang=en&referrer=ck12Launcher&backUrl=https://interactives.ck12.org/simulations/physics.html. Set the mass of the crash test dummy to 70 kg and record this value below.

m =

??

kg

2. Collide the car with a stationary barrier. Use the slider on the right to set the velocity of the car to –30 m/s. Make sure the “Type of restraint” is set to “None”. Press play on the simulation.

3. Calculate the change in momentum and the impulse. Use the two graphs to determine the initial and final velocities of the dummy, as well as the impulse imparted to the dummy. Calculate the initial momentum, the final momentum and the change in the momentum. Record all these values, along with the impulse in the table below. Show your calculations here.

Show work here or insert a picture of your work.

4. Compare the change in momentum to the impulse. How does the impulse delivered by the barrier compare to the change in momentum of the dummy? Calculate the % difference of the impulse compared to the change in momentum.

pi

pf

Δp

impulse

% difference

Is this what you expected? Explain.

Type response here.

5. Consider a safer collision. Use the slider under “Type of restraint” to select “Airbag” as your restraint.

Prediction: You will collide the car with the same initial velocity as before, but now the airbag is imparting the momentum to the dummy (instead of the dashboard and steering wheel). How will the initial velocity, final velocity, initial momentum, final momentum, maximum force and impulse change as a result of using the airbag?

Type response here.

6. Try the experiment. Press play on the simulation and observe the results.

Question: Were your predictions correct? Explain.

Type response here.

Question: What were the main differences in the force graph for the trial with no restraints and the trial with the airbag?

Type response here.

Question: In your own words, how does the airbag keep you safer during a collision? Try to incorporate force and impulse into your answer.

Type response here.

Activity 2: One-dimensional collisions: comparing forces

5. Set up for a two-cart collision. Use the simulation at https://interactives.ck12.org/simulations/physics/bumper-cars/app/index.html?screen=sandbox&lang=en&referrer=ck12Launcher&backUrl=https://interactives.ck12.org/simulations/physics.html. You will collide two bumper cars together.

Prediction: When the two cars collide, how would you expect the force vs. time graph for cart #1 to compare to the force vs. time graph for cart #2?

Type response here.

6. Collide the carts and record the results. Press the play button on the simulation. Observe the force measurements in the graph in the upper right hand corner.

Sketch the force graphs for the cars on the axis below, or draw the graphs on a separate piece of paper and attach your graphs to this document. Show both graphs on the same axis.

F (N)

t (s)

Question: Did the force vs. time graphs match your prediction? If not, explain why.

Type response here.

7. Try a collision with unequal masses. Now increase the mass of the blue car to 400 kg, and decrease the mass of the red car to 100 kg.

Prediction: How would you expect the force vs. time graphs for the red and blue cars to compare in this case, when the cars have unequal masses?

Type response here.

F (N)

t (s)

8. Collide the carts and record the results. Press play on the simulation.

Question: Did the force vs. time graphs match your prediction? If not, explain why.

Type response here.

Question: How do your results relate to Newton’s third law?

Type response here.

Activity 3: Different types of collisions

9. Set up to use different cars. Use the simulation at https://www.physicsclassroom.com/Physics-Interactives/Momentum-and-Collisions/Collision-Carts/Collision-Carts-Interactive. Click on the upper right corner of the simulation window to go to full screen.

10. Observe some inelastic collisions. Click on the button for “Inelastic collisions”.

A) Collide the carts with equal masses and equal and opposite velocities.

First record the masses of the carts.

mred =

??

kg

mblue =

??

kg

Click start to send the carts towards each other.

Describe the results of the collision (i.e. describe what happened in the collision how the carts are moving afterwards), then fill in the table below:

Type response here.

Before collision

After collision

v (red)

v (blue)

p (red)

p (blue)

p (total)

B) Press “Reset” in the upper left corner. Put one mass bar in the blue cart.

mred =

??

kg

mblue =

??

kg

Give the blue cart a greater velocity than the red cart before the collision. Press “Start” to send the carts towards each other.

Describe the results of the collision, then fill in the table below:

Type response here.

Before collision

After collision

v (red)

v (blue)

p (red)

p (blue)

p (total)

C) Put two mass bars on the blue cart, and record the masses.

mred =

??

kg

mblue =

??

kg

Give the blue cart a lower velocity than the red cart.

Describe the results of the collision, then fill in the table below:

Type response here.

Before collision

After collision

v (red)

v (blue)

p (red)

p (blue)

p (total)

11. Observe some elastic collisions. Click on the button that says “Elastic Collisions”. When these carts collide, almost no energy is lost in the collision. This kind of collision is called an elastic collision.

mred =

??

kg

mblue =

??

kg

A) With no mass bars on the carts, give the red cart an initial velocity of zero, and send the blue cart towards it.

Describe the results of the collision, then fill in the table below:

Type response here.

Before collision

After collision

v (red)

v (blue)

p (red)

p (blue)

p (total)

B) With the setup as in part A, send the carts towards each other with equal velocities.

mred =

??

kg

mblue =

??

kg

Describe the results of the collision, then fill in the table below:

Type response here.

Before collision

After collision

v (red)

v (blue)

p (red)

p (blue)

p (total)

C) Repeat the previous setup, but place a mass bar in one of the carts.

mred =

??

kg

mblue =

??

kg

Describe the results of the collision, then fill in the table below:

Type response here.

Before collision

After collision

v (red)

v (blue)

p (red)

p (blue)

p (total)

Discussion: If momentum is conserved, you would expect the total momentum after the collision to be the same as the total momentum before the collision. Experimentally, you would expect the percent difference between the momentum before and the momentum after to be small (or, if the total momentum is close to zero, you would expect the difference between the total momentum before and the total momentum after to be small compared to any of the individual momenta of the carts).

Question: Within the accuracy of the experiment, was momentum conserved in these collisions? Explain.

Type response here.

©Jonathan Cole, MiraCosta College, Oceanside, CA

©Jonathan Cole, MiraCosta College, Oceanside, CA. Updated by Erika Peters 2016.

©Jonathan Cole, MiraCosta College, Oceanside, CA. Updated by Erika Peters 2016.