Momentum, Energy and Collisions Scoring Sheet
Name ______Date______Hr. ____
1. Student answered preliminary questions and explained reasoning ______4 pts
2. Mass of carts recorded correctly ______2 pts
3. Velocity table recorded correctly ______5 pts
4. Momentum table filled out and calculated correctly ______7 pts
5. Kinetic energy table filled out and calculated correctly ______7 pts
6. Explained ratio for conservation of momentum ______1 pt
7. Explained ratio for conservation of KE ______1 pt
8. Explained whether momentum is conserved in each of the
three types of collisions based on the ratio and lab uncertainties ______5 pts
9. Explained whether kinetic energy is conserved in each of the
Three types of collisions based on the ratio and lab uncertainties ______5 pts
10. Student has classified the three types of collisions ______3 pts
Total ______40 pts Momentum, Energy and Collisions
Name ______Date ______Hr. ____
Introduction For two interacting objects, if there is no net external force then we expect the total momentum of the system to be conserved. In contrast, energy is only conserved when certain types of forces are exerted between the objects.
Collisions are classified as elastic (kinetic energy is conserved), inelastic (kinetic energy is lost) or completely inelastic (the objects stick together after collision). Sometimes collisions are described as super-elastic, if kinetic energy is gained. In this activity you will test for conservation of momentum and conservation of energy for different types of collisions.
Preliminary Questions
1. If two carts with magnetic bumpers are pushed together such that the carts interact by repulsion of the magnetic fields surrounding the magnets, predict what sort of collision (described above) would take place. Explain your reasoning!
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2. If two carts with Velcro strips on their ends are pushed together, predict what sort of collision (described above) would take place. Explain your reasoning!
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Procedure
1. Place a motion detector at each end of the track. Connect them to DIG/SONIC 1 and DIG/SONIC 2 channels of the interface. 2. Open the file “19 Momentum Energy Coll” from the Physics with Computers folder. 3. Measure the masses of the two carts and record them in the data table.
4. Place two carts at rest in the middle of the track. Click: zero – both sensors - ok
5. With the magnetic bumpers facing each other push one cart gently towards the other. (Cart 2 should initially be at rest before the collision. Make sure that the motion detectors are tracking each cart throughout the whole motion. Adjust if necessary. Use statistics to determine the initial and final velocity of each cart. Enter these values into the table. Repeat. (record your answers as runs one and two in the data table)
6. With the Velcro bumpers facing each other push one cart gently towards the other. Use statistics to determine the initial and final velocity of each cart. Enter these values into the table. Repeat. (runs three and four)
7. With the magnetic bumpers facing the Velcro bumpers push one cart gently towards the other. Use statistics to determine the initial and final velocity of each cart. Enter these values into the table. Repeat. (runs five and six) Data Table
Mass of cart 1 (kg) Mass of cart 2 (kg)
Run Velocity of Velocity of Velocity of Velocity of number cart 1 cart 2 cart 1 after cart 2 after before before collision collision collision collision (m/s) (m/s) (m/s) (m/s) 1 0 2 0 3 0 4 0 5 0 6 0
Run Momentum Momentum Momentum Momentum Total Total Ratio of number of cart 1 of cart 2 of cart 1 of cart 2 momentum momentum total before before after after before after momentum collision collision collision collision collision collision after/before
(kg•m/s) (kg•m/s) (kg•m/s) (kg•m/s) (kg•m/s) (kg•m/s) 1 0 2 0 3 0 4 0 5 0 6 0
Run KE of KE of KE of KE of Total KE Total KE Ratio of number cart 1 cart 2 cart 1 cart 2 before after total KE before before after after collision collision after/before collision collision collision collision (J) (J) (J) (J) (J) (J) 1 0 2 0 3 0 4 0 5 0 6 0 Analysis
1. Determine the momentum (mv) of each cart before the collision, after the collision, and the total momentum before and after the collision. Calculate the ratio of the total momentum after the collision to the total momentum before the collision. Enter the values in your data table. Show example calculations for one row on a separate sheet of paper. 2 2. Determine the kinetic energy (½ mv ) for each cart before and after the collision. Calculate the ratio of the total kinetic energy after the collision to the total kinetic energy before the collision. Enter the values in your data table. Show example calculations!
3. If the total momentum for a system is the same before and after the collision, we say that momentum is conserved. If momentum were conserved, what would be the ratio of the total momentum after the collision to the total momentum before the collision?
4. If the total kinetic energy for a system is the same before and after the collision, we say that kinetic energy is conserved. If kinetic were conserved, what would be the ratio of the total kinetic energy after the collision to the total kinetic energy before the collision?
5. For your six runs, inspect the momentum ratios. Even if momentum is conserved for a given collision, the measured values may not be exactly the same before and after due to measurement uncertainty. The ratio should be close to one, however. Is momentum conserved in your collisions? Which type of collisions show conservation of momentum?
6. Repeat the preceding question for the case of kinetic energy. Is kinetic energy conserved in the magnetic bumper collisions? How about the Velcro collisions? Is kinetic energy consumed in the third type of collision studies? Classify the three collision types as elastic, inelastic, or completely inelastic.