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Phy 201
Your 'cq_1_00.1' 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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The problem:
You don't have to actually do so, but it should be clear that if you wished to do so, you could take several observations of positions and clock times. The main point here is to think about how you would use that information if you did go to the trouble of collecting it. However, most students do not answer these questions in terms of position and clock time information. Some students do not pause the video as instructed. To be sure you are thinking in terms of positions and clock times, please take a minute to do the following, which should not take you more than a couple of minutes:
Pick one of the videos, and write down the position and clock time of one of the objects, as best you can determine them, in each of three different frames. The three frames should all depict the same 'roll' down the ramp, i.e. the same video clip, at three different clock times. They should not include information from two or more different video clips.
For each of the three readings, simply write down the clock time as it appears on the computer screen, and the position of the object along the meter stick. You can choose either object (i.e., either the pendulum or the roll of tape), but use the same object for all three measurements. Do not go to a lot of trouble to estimate the position with great accuracy. Just make the best estimates you can in a couple of minutes.
Which object did you choose and what were the three positions and the three clock times?
answer/question/discussion: ->->->->->->->->->->->-> scussion (start in the next line):
I chose the pendulum.
20.781 sec about 12in
21.0 sec about 15in
21.437 about 19in
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In the following you don't have to actually do calculations with your actual data. Simply explain how you would use data of this nature if you had a series of several position vs. clock time observations:
If you did use observations of positions and clock times from this video, how accurately do you think you could determine the positions, and how accurately do you think you would know the clock times? Give a reasonable numerical answer to this question (e.g., positions within 1 meter, within 2 centimeters, within 3 inches, etc; clock times within 3 seconds, or within .002 seconds, or within .4 seconds, etc.). You should include an explanations of the basis for your estimate: Why did you make the estimate you did?
answer/question/discussion: ->->->->->->->->->->->-> scussion (start in the next line):
You could determine the positions within about 2 inches and the clock times within about 1 second. I estimated the accuracy of the position by observing that it is very hard to tell what the tape measure says, so I just counted the black lines which were inches. But the pendulum is a lot bigger than the lines and it blocks you from being about to read exactly where the the pendulum is according to the tape measure. I am guessing that the pendulum is about 2 in wide which is why I am guessing that you can accurately get the position within 2 inches. I estimated the accuracy of the time by observing how quickly the timer went off and the shutter speed affects how clear the number are on the clock. It seemed like the tenths place after the decimal place could get pretty blurry, which is why I guessed that the time is only accurate within 1 second.
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How can you use observations of position and clock time to determine whether the tape rolling along an incline is speeding up or slowing down?
answer/question/discussion: ->->->->->->->->->->->-> scussion (start in the next line):
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How can you use observations of position and clock time to determine whether the swinging pendulum is speeding up or slowing down?
answer/question/discussion: ->->->->->->->->->->->-> scussion (start in the next line):
You could catalogue several observations for both time and position. Then you could figure out the difference between each position and put those numbers in a third colums. If the differences increase as time increases them the tape is speeding up and if they are decreasing then the tape is slowing down.
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Challenge (University Physics students should attempt answer Challenge questions; Principles of Physics and General College Physics may do so but it is optional for these students): It is obvious that a pendulum swinging back and forth speeds up at times, and slows down at times. How could you determine, by measuring positions and clock times, at what location a swinging pendulum starts slowing down?
answer/question/discussion: ->->->->->->->->->->->-> scussion (start in the next line):
You would construct the third column of differences in position, like in the question before except using the position of the pendulum instead of the tape. You would try to take as many observations as you can as often as you can. Then compare all the differences. The point at which the difference at one point is not as big as the difference before it is the position which the pendulum starts slowing down.
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Challenge (University Physics students should attempt answer Challenge questions; Principles of Physics and General College Physics may do so but it is optional for these students): How could you use your observations to determine whether the rate at which the tape is speeding up is constant, increasing or decreasing?
answer/question/discussion: ->->->->->->->->->->->-> scussion (start in the next line):
Look at the differences column once again. Look at the values that are increasing. If the difference is more than the previous difference than the rate is increasing. If the difference is less than the previous difference then the rate is decreasing. And if the differences are the same or about the same throughout then the rate is constant.
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&#Very good responses. Let me know if you have questions. &#