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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: ->->->->->->->->->->->-> (start in the next line):
I choose the roll of tape to observe. In the first position the roll of tape is at the beginning and has not moved. The first clock time is 57.390. In the second position, the roll of tape is about in the middle. The second clock time is 59.796. In the third position, the roll of tape is at the end of the ramp. The third clock time is 60.125.
???It took me a few tries to get used to the fastness of the video, but I believe I completed this part correctly.
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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):
I don't believe I could determine the positions and clock times very accurately. The video quality is not the best, therefore that may cause lag in the video and timing. So to be exact I would say that the positions could be estimated within 2-3 inches, since that is the easier to see than cm. I could estimate the clock times within 0.5-1 second, it seems that the timing is pretty on target other than the possible lag I mentioned earlier due to the video quality.
??? Since the video quality was hard to read, I can't say for certain that my estimates are right, I also did not see the black marker labeling the 1-foot mark.
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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): You can utilize the observations of position and clock time to determine whether the tape rolling along an incline is speeding up or slowing down. The clock time proves that the ramp makes the tape speed up by the smaller gaps in time as the tape rolls down. The position of the tape at the end when it bounces off the end shows the intensity. The tape roll hits the end hard, and bounces back pretty far in comparison to the whole length of the measuring tape. Therefore these observations prove that the tape is speeding up as it goes down the ramp.
??? Not sure if this is the correct answer, I had trouble pausing the videos so fast since they were all less than 10 seconds!
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The decreasing time intervals for equal distances (and I assume you were observing equal distance intervals) are excellent evidence that the tape is speeding up.
It's also very good to notice the bounce, as you did. Very observant.
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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):
I would use the position of the roll of tape to determine whether or not the pendulum is speeding up or slowing down, as well as using the clock to determine the speed of the pendulum. When the roll of tape is sped up I compared it to the pendulum and noted that the roll of tape was going faster than the pendulum. I also looked at the time, when I paused the video, the pendulum hand't moved as much as the roll of tape from the previous time I had paused it.
???Not sure if my reasoning is correct, but I believe that the pendulum was speeding up, but slower than the roll of tape.
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Again, you are making excellent observations.
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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): I am not sure exactly how to determine how the pendulum slows down and speeds up at times. The only reasonable conclusion I can come to is based on the air resistance. If the pendulum is more towards the peak of either side then it will speed up, where as when it is going back up onto the other side of the swing, it may be slower since it is going against gravity.
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Air resistance would be part of an explanation of the motion of the pendulum, but from the tape you aren't likely to be able to prove whether the pendulum was moving through air or through a vacuum (actually if you hear the sound it isn't moving through a vacuum, but you will understand my point).
The idea you've used in other answers, observing clock times and positions, is the best way I can think of to use data to answer the question.
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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): I would have to pause the video quite a bit with the clock times to note whether the tape is speeding up, staying constant, or slowing down. I would calculate the start time and the end time, then a few more times in between. I am not sure how I would use the positions though.
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Excellent work. Check my notes.
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