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Atwood Lab

Atwood Lab

Purpose:

The purpose of this lab is to determine how the ∆m and the ∑m affect the acceleration of the Atwood system.   We will then use this formula for a live trial of the Atwood Machine to approximate the acceleration due to gravity on earth.

Info

  1. Developed by George Atwood in 1784.

  2. Created by hanging two masses of unequal mass from different sides of a pulley system.

  3. You will be tracking ∆m, the difference in mass between the two sides and ∑m, the total mass of the system.

Part 1:  Acceleration vs. ∆m (Virtual)

  1. Open up the program found here.

  2. Set your planet to Vesta, the moon, or mars to further slow down the progress of the experiment.

  3. Decide on a ∑m for your system by looking at the largest masses you can have for mass one and mass two.  Note, mass two can never be bigger than mass one in the program, so maximize mass one to see what the greatest mass you can use is and then minimize mass two in order to see what the smallest allowed mass is for your experiment.  You can pick any ∑m you want as long as you will be able to 8 different ∆m using the ∑m you choose.

  4. Set up the ∆m and ∑m for your system and then hit the start button.  Use your velocity-time graph to find the acceleration of your system.

  5. Create a table that lists m1, m2, ∆m, and a.  Repeat this procedure of a total of 8 different ∆m.

  6. Make a graph of acceleration vs. ∆m.  Put graph and equation in your lab book

Part 2:  Acceleration vs. ∑m (Virtual)

  1. Keep your planet set to the same one you had it set for part 1.

  2. Decide on a ∆m for your system.  Do not change your ∆m for the remainder of this part.   You can pick any ∆m you want as long as you will be able to 8 different ∑m using the ∆m you choose.

  3. Set up the ∆m and ∑m for your system and then hit the start button.  Use your velocity-time graph to find the acceleration of your system.

  4. Create a table that lists m1, m2, ∑m, and a.  Repeat this procedure of a total of 8 different ∑m.

  5. Make a graph of acceleration vs. ∑m.  Put graph and equation in your lab book.

  6. Show your results to your teacher and if the results are good, you may start the live part of the experiment.

Part 3:  Acceleration vs. ∆m (Live Quantitative)

  1. Attach each of your water bottles to a short string and a paper clip.  You will be using hanging this system from the longer string you will be putting between your Atwood pulleys.



  2. Label one bottle m1 and one bottle m2.  Remove half of the water from bottle m2 and dump it down the drain.

  3. At this point the total water in the two bottle should not be changed.  So, from this point on,  when you remove water from one bottle make sure all of it goes into your other bottle.

  4. Try as best as possible to almost equalize the water between the two bottles, but with just a slightly larger amount in bottle 1.  You want m1 just slightly bigger than m2.

  5. Create an Atwood let up like the one you see in this picture.   Transfer this lab setup into your lab book.






  6. Bring bottle 2 down to table level and then release the bottle.  Watch the motion of the two bottles.  Describe the rate at which the bottles accelerate.

  7. What would happen if the two bottles had exactly the same mass?

  8. Over a series of 5 trials, move water from bottle 2 into bottle 1.  At the end of the 5th trial you should have bottle 1 filled and bottle 2 about half way filled.

  9. Describe the changes to the motion that you noticed each time you moved more water to bottle 1.

Part 4:  Measuring Acceleration for Live System

  1. At this point you should have bottle one filled with water and bottle two approximately half filled with water.  Get the mass of these bottles (including water, cap, string and clip) using your triple beam balance.

  2. Record these masses in your notebook and then carefully set up your system with mass 1 at the highest point, mass 2 at the lowest point and a meter stick clearly placed right near one of the two bottles.

  3. Set your phone to record your video at the greatest frame rate it is capable of recording.  Set up the phone so that it cannot move while recording the motion of your system.  Feel free to borrow my tripod when you are ready to record.

  4. Set the camera up so its height is midway between your two bottles.

  5. With the greatest of care, release the system and record the progress of at least one of the bottles.

  6. Send the movie to a computer (dropbox and google drive are best).  If the movie does not retain the higher frame rate, open it in iMovie on your device and then export it and send it to dropbox or google drive again.

  7. Import the video into Logger Pro and track the motion of the bottle to determine its acceleration.

  8. Use your acceleration and the formula we developed in part 1 and 2 to determine the acceleration due to gravity on earth.
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