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PHY 202
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: ->->->->->->->->->->->-> (start in the next line):
Pendulum:
7 inches at 20.562 s
10 inches at 20.671
12 inches at 20.781
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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: ->->->->->->->->->->->-> (start in the next line):
The estimates of positions would be accurate within ½ inch at most. It is relatively easy to see the marks for each inch along the measuring tape, and a student might estimate within one-half of an inch if the object appears to be between the inch-marks, but it is not likely to accurately estimate anything smaller than that. The size of the pendulum itself makes it difficult enough to determine whether it is at the half-inch or the full inch-mark that it is obscuring.
The clock times would be accurate to the thousandths of a second, as accurate as the computer is. This is simple enough to observe; when the video is paused the clock time is paused and visible without question.
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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: ->->->->->->->->->->->-> (start in the next line):
If the tape rolling down the incline is speeding up, its gain in position should increase at an increasing rate with each gain in time. For example, it may roll 1 inch in the first second but 3 inches in the last second.
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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: ->->->->->->->->->->->-> (start in the next line):
If the pendulum is speeding up, its gain in position should increase at an increasing rate with each subsequent gain in time. The distance gained in the last time interval should be greater than the distance gained in the first. If it is slowing down, the opposite should occur. Its distance gain would thus be greater in the first time interval than the last.
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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: ->->->->->->->->->->->-> (start in the next line):
The pendulum speeds up in the descent portion of its swing and slows down in the ascent portion as it works against gravity. Thus, each subsequent time interval in the former should reveal larger and larger gains in position - until the halfway point. Beyond the halfway point, on its ascent, each subsequent time interval should show smaller and smaller gains in position.
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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: ->->->->->->->->->->->-> (start in the next line):
If the position gains are increasing at an increasing rate, then the tape is speeding up. If position gains are the same for each time interval, then the tape is speeding up at a constant rate. If the position increases but at a decreasing rate (thus the change in position would be getting smaller and smaller with each passing time interval), then the rate of the tapes speeding up would be decreasing.
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Very good throughout.
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