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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):
The object that I chose was the pendulum. I used video 2 as reference video. Each position was measured from the front side (left side) of the pendulum. The measurements and times are as follows:
Position Measurement Position Time
1 5 inches 40.578
2 11 inches 40.796
3 20 inches 41.234
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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 believe that if you were to observe the positions and clock times from the given video, you could accurately determine the position to within 1 inch and the time to within .1 seconds.
The position of an object can be measured to the nearest 1 inch because you have clearly marked inches on the ruler. At any time when you stop the video, you can count the inches from the left or right and be fairly accurate to the inch.
When it comes to the time factor, it would be difficult to measure more accurately than 0.1 second. Even though the timer may go in intervals of 0.01 second, the movement of an either object is relatively slow and thus your time for a given position could not be extremely accurate. To the naked eye, the object might not have appeared to move but the time in .01 second could be different, therefore I believe .1 second is as accurate as you could be.
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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):
In order to determine whether the tape is speeding up or slowing down, a person could take the change in distance traveled and divide it by the time it took to make that change to determine if the rate was speeding up or slowing down.
If it took less time to cover the same distance, the tape would be speeding up, but if it took more time to travel the same distance, the tape would be slowing down.
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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):
In a similar fashion to determining if the tape is speeding up or slowing down, the pendulum can be measured in the same way. Take the difference in position and divide it by the difference in time to determine if the rate is increasing or decreasing and thus if the pendulum is speeding up or slowing 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): 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):
By taking various position and time measurements, one could look at the changes in rate at several points along the path of the pendulum swing. When the rate decreased, the pendulum would be shifting from speeding up to slowing down.
I believe that just after the pendulum reaches the bottom of its swing, it will begin to slow down due to gravity pulling back on it.
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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):
By looking at the difference in time over the same changes in position, one could determine if the tape was slowing down, increasing, or constant.
If the amount of time need to cover the same distance is less, then the tape is speeding up. If it takes more time to cover the same distance, the tape is slowing down. Finally, if it takes the exact same time to cover the exact same distance, then the rate of the tape's movement is constant.
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@& Very good responses. Good insight and good explanations.*@
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