Conservation of Momentum

Conservation of Momentum

Physics 111 Lab

In this experiment, you will determine if momentum is really conserved in a specific perfectly inelastic collision.

The collision here will be between two carts:

BEFORE AFTER

In the “BEFORE” picture, one cart moves while the other is at rest. The two carts collide and stick, and move off together at a new velocity. You will measure the momentum before and after the collision, and compare these two values to see if they are the same.

·  Unless you can come up with a more precise and accurate way of measuring things, use the motion detector and laptop to determine the speed of the carts before and after the collision. You can get the uncertainty in the speed by seeing how the speed varies on the v vs. t graph.

·  MAKE SURE YOUR MASSES ARE SIGNIFICANTLY DIFFERENT FROM EACH OTHER. Since all our carts have roughly the same mass, you will need to add weight to one (or both) cart(s). It doesn’t matter which one is heavier.

·  The momentum before the collision is the same as the momentum after the collision ONLY if their uncertainty ranges overlap!

The usual report is required:

Name/Partners/Date/Title

Introduction – State the purpose of the experiment.

Theory – Derive expressions for the momentum before and after the collision. These expressions must be in terms of quantities you directly measure (or can read off of computer).

Experiment – Say here what you did in order to take data. Pretend this document doesn’t exist, and include enough detail that someone 10 years from now could duplicate your experiment. Don’t forget equipment #’s, a diagram, and all of your data. If you need a piece of equipment and don’t see it, ask me. Include a printout of your v vs t plot and your data. How will you determine the uncertainty in vi and vf?

Analysis – Here you crunch your numbers. Determine the momentum before with uncertainty, and the momentum after with uncertainty.

Discussion – Was momentum conserved in this collision? Why or why not? If you get a result you did not expect, go back and check your work! If you made a mistake, go back and fix it, retaking data if necessary. Don’t turn in flawed results.

Conclusion – Repeat/sum up your conclusion as to whether momentum was conserved or not, and why it was or was not.