, Energy and Collisions The of two carts on a track can be described in terms of conservation and, in some cases, energy conservation. If there is no net external force experienced by the system of two carts, then we expect the total of the system to be conserved. This is true regardless of the force acting between the carts. In contrast, energy is only conserved when certain types of forces are exerted between the carts. Collisions are classified as elastic (kinetic energy is conserved), inelastic (kinetic energy is lost) or completely inelastic (the objects stick together ). Sometimes s are described as super-elastic, if kinetic energy is gained. In this experiment you can observe completely inelastic s and test for the conservation of and energy. PROCEDURE. Measure the masses of your carts and record them in your data table. Label the carts as cart and cart.
. Set up the track so that it is horizontal. Test this by releasing a cart on the track from rest. The cart should not move.. Practice creating gentle s by placing cart at rest in the middle of the track and release cart so it rolls toward the first cart, Velcro bumper toward Velcro bumper. The carts should stick together the and roll smoothly away from the site.. Place a Motion Detector at the cart end of the track. Always roll cart from this end of the track.. If your Motion Detector has a switch, set it to Track. Connect the Motion Detector to DIG of LabQuest and choose New from the File menu. If you have an older sensor that does not auto-id, manually set up the sensor. 6. Start data collection. Repeat the you practiced above. Make sure you keep your hands out of the way of the Motion Detector you push the cart. 7. Use the graph of position vs. time to verify that the Motion Detector can track the cart properly throughout the entire range of motion. You may need to adjust the position of the Motion Detector. If necessary, repeat to the previous step. 8. From the velocity graph you can determine an average velocity and the for each cart. You should see two approximately constant regions in your velocity graph, corresponding to the cart speed the and then the speed of the two carts together the. If you cannot see two such regions, repeat data collection. To repeat, return to Step 6. 9. Measure the average velocity during the time interval the. a. Tap and drag your stylus across the region of the graph that corresponds to the first constant velocity region to select the region. b. Choose Statistics from the Analyze menu. The mean velocity for the time interval will be displayed. Record this as the initial velocity in your data table. 0. Measure the average velocity during the time interval the. a. Tap and drag across the region of the graph that corresponds to the second constant-velocity region to select the region. b. Choose Statistics from the Analyze menu. The mean velocity for the time interval will be displayed. Record this as the initial velocity in your data table.
Note that the carts have the same velocity since they are stuck together. c. Choose Statistics from the Analyze menu to turn off statistics.. Repeat the and analysis four more times for a total of five runs. DATA TABLE Mass of cart (kg) Mass of cart (kg) Run Number Velocity of cart the Velocity of cart the Velocity of cart the Velocity of cart the Run Number of cart of cart of cart of cart Total Total Ratio of total / Run Number KE of cart KE of cart KE of cart KE of cart Total KE Total KE Ratio of total KE /
ANALYSIS. Determine the (mv) of each cart the, the, and the total and the. Calculate the ratio of the total the to the total the. Enter the values in your data table. Show an example calculation in the analysis.. Determine the kinetic energy (½ mv ) for each cart and the. Calculate the ratio of the total kinetic energy the to the total kinetic energy the. Enter the values in your data table. Show an analysis calculation in the analysis.. If the total for a system is the same and the, we say that is conserved. If were conserved, what would be the ratio of the total the to the total the? Explain.. If the total kinetic for a system is the same and the, we say that kinetic energy is conserved. If kinetic were conserved, what would be the ratio of the total kinetic energy the to the total kinetic energy the? Explain.. For your three runs, inspect the ratios. Even if is conserved for a given, the measured values may not be exactly the same and due to measurement uncertainty. The ratio should be close to one, however. Is conserved in your s? Refer to your data and provide support for your answer. 6. Repeat the preceding question for the case of kinetic energy. Is kinetic energy conserved in your completely inelastic s? Refer to your data and provide support for your answer. CONCLUSION: This is a little different than most conclusions we have done since you did not form a hypothesis. Your conclusion needs to state whether or not you were able to confirm what you have been taught about conservation of and what the lab told you about conservation of kinetic energy. It needs to be a statement which summarizes the main points you learned in the lab about and kinetic energy for perfectly inelastic s.
Lab Write-up Requirements: Title Background This will be the answers to the preliminary questions. Your answers need to be complete sentences. Materials Include a diagram. Procedure The procedure does not need all the technical information included in the first lab. Be brief while also being thorough. Data Include tables and any example calculations of any numbers in the tables which are not direct measurements. Analysis Discuss your data!!! You need to include a method of determining the error in the lab. That can be ratios like the original lab, or you may come up with a different way of determining whether or not your data shows conservation of and conservation of kinetic energy. Conclusion - It needs to be a statement which summarizes the main points you learned in the lab about and kinetic energy for the particular situation you chose. EXTENSION (This will be a completely separate lab!!) **The following extensions require two Motion Detectors. Use a second Motion Detector to measure the speed of cart. Choose of the following extensions. Write a lab to investigate the situation and complete the lab activity.. Explore elastic s by measuring the speeds of carts and separately. Use magnetic bumpers to study elastic s, and magnetic-to-velcro s to study inelastic (but not completely inelastic) s.. Using a cart with a spring plunger, create a super-elastic ; that is, a where kinetic energy increases. The plunger spring should be compressed and locked the, but then released during the. Measure and the. Is conserved in this case? Is energy conserved?. Using the magnetic bumpers, consider other combinations of cart mass by adding weight to one cart. Are or energy conserved in these s?. Using the magnetic bumpers, consider other combinations of initial velocities. Begin with having both carts moving toward one another initially. Are and energy conserved in these s?