phy 121
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 to record the position of the tape at several intervals.
Time-40.687, Position-8.5”; Time-40.796, Position-10.5”; Time-41.016, Position-16”
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:
The clock times should be accurate to .001 seconds, because when we pause the video we can clearly see the time expressed to .001 seconds. My measurements should be accurate to about ¾ of an inch, because the tape was blurry enough that I could not make it too accurate, but I was able to see it well enough to keep the inaccuracy under 1 inch.
• 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:
I could determine the change in time and the change in position for each interval, then determine the average rate at each interval.
• 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:
To determine whether the swinging pendulum is speeding up or slowing down, I would use the same method described in reference to the tape.
• 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:
By calculating the average rate over smaller and smaller intervals, even approaching zero, we could narrow it down until we find the point where the pendulum starts slowing down.
• 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:
If we calculated the average rate for each interval, we could determine whether the change in average rate over the different intervals was constant, increasing, or decreasing.
Check to see that you have followed the instructions:
• The instructions told you to pause the video multiple times. It appears that some students are not following this instruction.
If you haven't used the 'pause' and 'play' buttons on your media player, you should go back and do so.
• The questions are phrased to ask not only what you see when you play the video, but what you see when you pause the video as instructed, and what you think you could determine if you were to actually take data from the video. You aren't asked to actually take the data, but you need to answer how you would use it if you did.
It's OK if you have given more general descriptions, which are certainly relevant. But answers to the questions should include an explanation of how you could use the series of position and clock time observations that are may be observed with this video.
• The questions also ask how much uncertainty there would be in the positions and clock times observable with this specific video. Different people will have different answers, and some reasonable answers might vary from one clip to the next, or from one part of a clip to another. However the answers should include a reasonable quantitative estimate (i.e., numbers to represent the uncertainty; e.g., .004 seconds of uncertainty in clock times, 2 inches in position measurements. Use your own estimates; neither of these example values is necessarily reasonable for this situation). You should also explain the basis for your estimate: why did you make the estimate you did?
You should have estimated the number of seconds or fraction of a second to within which you think the time displayed on the computer screen might be accurate (e.g., is it accurate to within 10 seconds of the actual clock time, or to within 1 second, within .1 second, maybe even within .01 or .001 second). You might not yet know enough about the TIMER to give an accurate answer, but give the best answer you can.
You should also indicate a reasonable estimate of the number of inches or fraction of an inch to within which you could, if asked, determine the position of each object.
I believe I have followed each of these instructions.
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It is hard for me to determine, because I am up and down doing things for my kids. Maybe 30 minutes or so...
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&#Very good work. Let me know if you have questions. &#