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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 observed the roll of tape.
40.578 it is around 4-5 inches
40.796 it is around 1 foot and more visible
41.234 it has reached the end and bounced back about 2-3 inches
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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):
Because the timer shows time to the nearest .001 second, you should be able to determine the clock time accurately. I am not really clear about how to tell the degree of accuracy (1 second, 0.1, or 0.01). I'm not sure what I'm looking for when that question is asked. Also, so much happens so fast in the video, I think that it will be difficult to tell exactly what is happening at any given time. I think that, even if the clock says 40.578, for example, calculating positions of objects at that exact moment will be a challenge. I think that measuring the position of the object can be done within 2 inches. This is for several reasons. With the roll of tape, it is hidden behind the pendulum for about half of the trip down the ramp. The tape is a couple of inches across, so that also adds to error in determining where it is located on the ramp. It has already been stated that the video is not the best quality, so for this experiment, you can't clearly see the inch markings.
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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):
It is easy to see the point at which the tape becomes faster than the pendulum because it emerges from behind it. To use the clock time, you could measure how far it went certain intervals (like check the clock every 3 inches) to see if the time decreased as it went down the ramp.
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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):
The swinging pendulum is interesting because it seems to have a steady speed because it's going back and forth. Obviously, it stops at either end of its swing, so it is speeding up and slowing down as it swings. Comparing it to the rolling tape, you can see the difference in the speeds. Comparing it to the tape measure and checking it at various speed intervals can help determine if it is speeding up or slowing down be seeing how much area it covers in a given amount of time. The biggest problem is that it is all over so quickly. It makes observations difficult.
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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 would think that you would need time-lapse capability and a system that is more responsive than this video and my computer. You would have to stop it inch-by-inch to see how fast it covers each inch to determine when it is speeding up and where it slows 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: ->->->->->->->->->->->-> (start in the next line):
You can see that the tape's speed is increasing because of the way it always pulls away from the pendulum. Unless the moment that the tape pulls away from the pendulum is the moment when the pendulum starts to slow down.
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&#Good work. Let me know if you have questions. &#