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Phy 201
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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Coll Labs Draft 3
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Collaborative Lab - Rotating Strap Experiment
Experimentalist Instructions
Objective: to determine which setup causes the greatest average velocity.
Materials needed:
• Metal Strap
• 2 Magnets from lab materials
• 1 die
• Ruler that measures in cm
• TIMER Program
Spin the strap and time it
You have a metal 'strap' (a thin strap of framing metal, a foot long and an inch or two wide) and a die (i.e., one of a pair of gaming dice) in your lab materials package.
• Place the strap on the die, similar to the way the straw was place on a die in one of the video clips you viewed under the line Introduction to Key Systems under the Introductory Assignment. It is not difficult to balance the strap on the die, provided the die rests on a level surface, so that it will stay on the strap when given a spin.
• Spin the strap (not too fast, so you can count its revolutions) and count how many times it goes around before stopping. For the experiment you will time how long it takes to come to rest between 2 and 3 rotations. To have some kind of consistency of the initial velocity, attempt to spin the strap so that it will make at least 2 revolutions, but the strap will come to rest at less than 3 rotations. As I have found it will take a little practice to get a consistent push. All of your trials will not come to rest between 2-3 rotations. Only count the trials that come to rest between 2-3 rotations.
Now repeat the spin but this time use the TIMER to determine how long it takes to come to rest after being released (i.e., after it loses contact with your finger). You can hold onto the clip with one hand and extend a finger of that hand to start the strap spinning, leaving your other hand free to operate the TIMER.
Repeat the process 4 times for a total of 5 trials. Throw out any trials that the strap does not make at least 2 revolutions and any trials that the strap comes to rest after making more than 3 rotations. Repeat the process until you have 5 trials that fit into the parameters. The strap must come to rest between 2-3 rotations for all trials that are reported.
A revolution consists of a 360-degree rotation of the strap about the axis. You should easily be able to count half-revolutions and then estimate the additional number of degrees, to come up with the rotation within an error of plus or minus 15 degrees or so. That's all the precision required here, so there is no need to bother with a protractor.
In the first line record the time followed by a comma and the number of degrees rotated. Record the other times and degrees in the following lines for a total of 5 lines for your 5 tests that fit the parameters of the experiment:
Put weights on the ends of the strap and repeat
Two magnets came with your materials. Attach them to the ends of the strap and repeat. Spin the strap. You can determine if the system is more stable and hence easier to use with the magnets on top of the strap, or hanging underneath it, but it should work either way.
Then repeat the above exercise.
Repeat for a total of 5 trials that fit the parameters.
Report your results as indicated:
• Report in the first line the time in seconds and the number of degrees of rotation from the time you released the strap to the instant it came to rest. Report one trial to each line just as you did before.
Measure the distance of the magnet from the axis or middle of the strap. Measure both the distance of the nearest point of the magnet and the furthest point of the magnet. Report the nearest point of the magnet in line 6 and the furthest point in line 7.
Move the weights 4 cm towards the center of the strap, then repeat the above exercise.
Repeat for a total of 5 trials that fit the parameters.
Report your results as indicated:
• Report in the first line the time in seconds and the number of degrees of rotation from the time you released the strap to the instant it came to rest. Report one trial to each line just as you did before.
Measure the distance of the magnet from the axis or middle of the strap. Measure both the distance of the nearest point of the magnet and the furthest point of the magnet. Report the nearest point of the magnet in line 6 and the furthest point in line 7.
Move the weights another 4 cm towards the center of the strap. The magnets should now be 8cm away from the end of the strap. Repeat the exercise as stated above for a total of 5 trials that fit the parameters. Report your results as indicated:
• Report in the first line the time in seconds and the number of degrees of rotation from the time you released the strap to the instant it came to rest. Report one trial to each line just as you did before.
Measure the distance of the magnet from the axis or middle of the strap. Measure both the distance of the nearest point of the magnet and the furthest point of the magnet. Report the nearest point of the magnet in line 6 and the furthest point in line 7.
Collaborative Lab - Rotating Strap Experiment
Analyst Instructions
Find the mean of the 5 times and the average amount of degrees rotated for the initial trials with no weights. Enter your data in comma-delimited format below:
Find the mean of the 5 times and the average amount of degrees rotated for the trials with the weights at the end of the strap. Enter your data in comma-delimited format below:
Find the mean of the 5 times and the average amount of degrees rotated for the trials with the weights at 4cm from the end of the strap. Enter your data in comma-delimited format below:
Find the mean of the 5 times and the average amount of degrees rotated for the trials with the weights at 8cm from the end of the strap. Enter your data in comma-delimited format below:
Divide the average number of degrees by the mean number of seconds for each trial. Enter the degrees/second of the first experiment in the first line. Enter the degrees per second in for the second experiment in the second line, degrees/second for the third experiment in the third line and degrees/second for the fourth experiment in the fourth line.
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I have changed the directions to have the experimentalist time how long it takes the strap to come to rest but the range has to be 2-3 rotations. I have also added back into the experiment that the number of degrees rotated must also be recorded.
Please let me know if you have any other suggestions for my experiment. Thank you for your help.
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This looks very good. Send it on to your experimentalist, if you haven't already done so.
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