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# Physics 211 Lab Six A. Introduction 1. The purpose of this experiment is to investigate what physical quantities are conserved (remain constant)...

Physics 211 Lab Six

A. Introduction 1. The purpose of this experiment is to investigate what physical quantities are conserved (remain constant) during collisions. 2. You make several sets of observations. Qualitative and quantitative. 3. This lab is completely computer based and requires no outside materials.

B. Preparation

1. Open your web browser and go to: http://alamo.nmsu.edu/~meydenbe/P211/AirTrack_Collisions.swf 2. The Momentum and Energy in Collisions Flash animation will appear. 3. Play with the program a bit to get a feel for it by: a. Click the Practice button. Click the Instructions button near the center at the bottom. b. Read the instructions then click Next (bottom left) c. Read the rest of the instructions then click Back d. You should be back at the practice screen. e. Turn on the air pump (press green button). If the sound is turned on, you will hear the air pump running. f. Click the red release handle. The spring will fire the cart down the track. g. Place the mouse over the round knob of the spring and drag it right to cock it. h. Drag cart 1 all the way right. (Note: If you reverse the last two steps, the cart will not move because there will be a gap between the end of the spring and the cart - try it! Drag the cart then cock the spring launcher) i. With the launcher cocked and cart 1 all the way right, drag cart 2 between the two gates (where it originally was) j. Click the switch collisions button to change to an inelastic collision then run the lab.

B. Procedure

1. Run 1: Totally inelastic collision with carts of equal mass a. Start the simulation in the practice section. b. Reset the track and adjust the sliders to give both carts a mass of 2.88 kg (or as close as you can get, you may not be able to get them exactly the same or exactly 2.88) c. Place cart 1 all the way to the right and cart 2 in the middle between the two photogates. d. Ensure the simulation is in the Inelastic mode. e. Assuming momentum is conserved, predict the velocity of the carts (vf(1+2))after the collision (use vi1 , vi2 as the initial cart velocities). f. Run the experiment. How do the results compare with your prediction(s)? 2. Run 2: Totally inelastic collision with carts of unequal mass a. Reset the lab. b. Change the mass of cart 2 to 5 kg (or as close as you can get to it) c. Repeat steps c-f of the previous run. 3. Run 3: Totally elastic collision with carts of equal mass a. Erase the trace and reset the lab.

b. Change the mass of each cart to 3.25 kg (or as close as you can get) and run the lab. c. How does your results compare with the run 1? 4. Run 4: Totally elastic collision with carts of unequal mass a. Erase the trace and reset the lab. b. Increase the mass of cart 1 to 6.51 kg and run the lab. c. What are your observations? 5. Run 5: Totally elastic collision with carts of unequal mass a. Erase the trace and reset the lab. b. Change the mass of cart 1 to 3.25 kg and cart 2 to 6.25 kg and run the lab. c. What are your observations? 6. Run 6: a. Erase the trace and reset the lab. b. Return to the main menu and select the Perform an Experiment option. c. Weight the carts. (Click the button and a window open. Drag the cart up and over the scale then let go of the mouse button. The cart should drop on the scale. If it misses, try again. Drag it off and weigh the other cart) d. Measure the length of the carts. (Drag the ruler to the cart - it's near impossible to read it very well. I expanded my Internet Explorer browser window by holding down the Ctrl key and rolling the mouse wheel to help but it still was hard to read. Make your best guess) e. Run the lab. The photogates give you the times elapsed as the cart travelled through. If cart 1 bounces (unequal mass) it will continue through a gate and the time will be recorded as time 2. Note if it was moving left or right as that will effect the momentum (or record the right clock as a negative number!) f. Record the results (mass, length, time(s)) of each cart in a spreadsheet.

g. Click the New Experiment button and repeat steps c, d, and e. The lengths and masses will have changed. h. Repeat step g for the third time. i. Calculate the initial and final velocities, kinetic energies, and momentum of each cart and total initial/final kinetic energy and momentum of the system.

7. Run 7: a. Repeat Run 6 except: change to an inelastic collision and only make 1 run. The final times for cart 1 and 2 will probably not be exactly the same which is a program error since the two carts are connected the must be the same! b. Record your results on a separate spreadsheet.

C. Summary 8. Summarize your results on the lab report. Was momentum conserved? Was energy conserved? Include spreadsheet data. (Copy and paste into Word is the preferred method) Formulas used in example spreadsheet:

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