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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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Collaborative Labs (roughdraft
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I have attached the first draft for my experiment using the rotating strap. I realize my experiment is pretty basic and I am open to any suggestions. I did copy and paste part of the instructions for our earlier experiment using the strap. It only made sense to use the same instructions because it is essentially the same experiment with a variation. Any suggestions are much appreciated. Thank you,
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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.
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), and through how many revolutions it travels. 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.
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.
Repeat the process 4 times for a total of 5 trials.
In the first line record the time followed by a comma and the number of degrees. Record the other times and degrees in the following lines for a total of 5 lines for your 5 tests:
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
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.
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In the original experiment a variety of initial velocities was used, resulting in a variety of displacements and time intervals. For this experiment I suggest controlling for one of these three variables (angular displacement, initial velocity, time interval). You can't control completely, but you can specify that only trials will count for which the chosen variable has value within, say, 10% of a specified value.
For example if you wanted to control for initial angular velocity, you could specify that the angular velocity should be within +-10% of 100 degrees / second, so that initial angular velocities would be between 90 deg / sec and 110 deg / sec.
Initial angular velocity would not be a good choice of the variable to control, since we can't measure it directly. Either angular displacement or time interval (i.e., the time required to come to rest) would be a better choice.
I'll leave it to you to specify which variable to control, what value of the variable to shoot for and what range of values is acceptable. Your experimenter would then discard trials for which that variable was out of range, obtaining 5 trials with the controlled variable in the specified range.
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You'll also want your experimenter to measure and report the distance of the magnet from the axis of rotation. I would suggest measuring both the distance to the nearest point of each magnet, and to the furthest point.
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Move the weights 4 cm towards the center of the strap, then repeat the above exercise.
Repeat for a total of 5 trials
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.
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. 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.
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 sent this to you in an email about a week ago because you had said in another email to the class that it was ok to do so. That is one reason why this is even later than it should be. I would appreciate any other suggestions you may have for my experiment. Thank you
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I apparently missed the email. My apologies.
Your plan is good, but since this is a refinement of an assigned experiment, it needs to give us even more specific information. I've asked you to choose one of two variables to control. I've also suggested you get the ctual measurements of the magnet positions.
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Check my notes and send me a draft as soon as possible. Both email and form would be a good idea.
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