Find the Lab
In your web browser, go to www.gigaphysics.com, then go to Virtual Labs, and then click
Conservation of Momentum.
If someone else used the computer for this lab before you, click New Experiment. This will
ensure that you have your own unique cart data when you do the experiment.
Part I: Measure the Carts
To find the length of the purple cart, use your mouse to drag the cart over the caliper in the
upper left corner of the lab. Convert the length to the SI unit of meters, then record your result
in the table below. Repeat for the green cart.
Find the masses of the carts by dragging each one in turn over the electronic balance in the
upper right corner. The balance reads in grams, so convert each mass to the SI unit of
kilograms, then record your data.
These measurements will stay the same as long as you don’t refresh the screen or click the button to start a new experiment. If you don’t complete the lab if one sitting and have to load the lab page again, the lengths and masses will change. If this happens, you will need to measure them again and use the new values for the remainder of the lab.
Part II: Determine the Carts’ Velocities
Select “same direction” from the Carts’ Direction menu and “inelastic” from the Collision
Behavior menu.
Click Start Carts to put the carts in motion. The red numbers you will soon see tell you how
many seconds it took each cart to pass through that photogate. If you lose track of which
photogate is measuring which cart, notice the purple and green arrows labelling each; a half
purple/half green arrow is used when both carts were stuck together as they passed through.
You can also click Start Carts if you want to watch the collision again.
Record your times in the data table at the top of the next page. Also copy the lengths from
part I. Be sure to add the lengths of the two carts when the carts are stuck together.
Calculate each cart’s velocity and enter it in the table as well.
Mass of purple cart Length of purple cart Mass of green cart Length of green cart
2
Part III: Calculating Momentum
Use the fact that momentum equals mass times velocity to calculate the momentum of each
cart. Remember to add the masses when the carts are stuck together.
Calculate the total momentum of the two carts before and after the collision.
You should find that the total momentum before and after the collision is identical (at least to
within rounding errors.) If you don’t, you should find out what went wrong and correct it before
you complete the next part.
Part IV: The Elastic Collision
This time, set the Carts’ Direction to opposite and the Collision Behavior to elastic. Repeat the
same steps as in part II and III. (The data table is at the top of the next page.)
When you calculate the velocities and momenta, signs matter.
Make sure that carts that are moving to the left have negative
velocities. If you lose track of which direction the carts were
going for each photogate, you have the arrows to help you, and
you can click Start Carts to watch the collision again.
Elapsed time Length Velocity
Purple cart before collision
Green cart before collision
Carts stuck together after collision
Mass Velocity (from part II) Momentum
Purple cart before collision
Green cart before collision
Carts stuck together after collision
Purple cart’s momentum Green cart’s momentum Total momentum
Before collision
After collision ——————– ———————-
3
Part V: One More Case
Repeat the experiment once more, this time with any combination of Carts’ Direction and
Collision Behavior you have not used already. Record which settings you use, then complete the
calculations as before.
Carts’ Direction ___________________________ Collision Behavior _________________________
Elapsed time Length Velocity (with sign!)
Purple cart before collision
Green cart before collision
Purple cart after collision
Purple cart before collision
Mass Velocity Momentum
Purple cart before collision
Green cart before collision
Purple cart after collision
Purple cart before collision
Purple cart’s momentum Green cart’s momentum Total momentum
Before collision
After collision
Elapsed time Length Velocity (with sign!)
Purple cart before collision
Green cart before collision
Purple cart after collision
Purple cart before collision
4
Part VI: Conclusions
What did you notice about the total momentum before the collision and the total momentum after
the collision in each of the above cases?
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The principle you should have noted in the previous question is called conservation of momentum.
What do you think it means to say something is conserved in the context of physics?
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Do you think there is any combination of conditions in this lab under which momentum would not
have been conserved? Explain your answer.
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Learning physics? Teaching physics? Check out www.gigaphysics.com.
© 2016, Donovan Harshbarger. All rights reserved. This activity guide may be reproduced for non-profit educational use.
Mass Velocity Momentum
Purple cart before collision
Green cart before collision
Purple cart after collision
Purple cart before collision
Purple cart’s momentum Green cart’s momentum Total momentum
Before collision
After collision
WE HAVE DONE THIS QUESTION BEFORE, WE CAN ALSO DO IT FOR YOU
GET SOLUTION FOR THIS ASSIGNMENT, Get Impressive Scores in Your Class on The Conservation of Momentum
