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: I chose the tape with the following positions with corresponding clock times:
4.75 in 20.453 sec, 10.25 in 20.671 sec, 1 ft 11 in. 21 sec
When the tape roll was blurry, where should I have measured?
All real-work data will be blurry at some level of precision. In this case, you should come up with a consistent standard for where to measure, and stick to it. Your data should include an estimate of the uncertainty in the measured positions, which will in some way be based on the extent of the blur and your assessment of how uncertain that makes your observations.
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: I think the measurements could be off a maximum of 1 inch. I think the clock time could be off .01 seconds possibly. Where the tape was blurry it spanned over and inch so that is why I estimate 1 inch. The clock on the computer seemed blurry in some places as well, and my guess is just the most educated guess I have.
Good. This is the sort of thing I was talking about above.
How are you supposed to know the error of the clock?
you can put limits on how often it might be changing, and you can also see if there are consistent intervals between successive times, or if those intervals are multiples of some common interval
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: You use the formula distance=rate*time. Take the three measurements you recorded and plug in distance and time to find the rates at the three points.
Isn't it possible with the blurriness of everything that you could conclude something incorrect?
You always need to acknowledge the limits on your accuracy; this case is no exception.
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: The same way as the tape, d=rt
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: Take as many measurements as possible and determine its rate of speed over specific distance intervals. Note its rate at a certain distance mark and you can compare to find the times it slows down/speeds up.
If you watched the whole process of a pendelum swing, couldn't you see where its speed is 0?
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: Again take as many measurements as possible and use d=rt.
With the tape, you could actually find its acceleration couldn't you?
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About 45 minutes.
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Excellent answers and questions. See my notes.