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Phy 231
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 picked Video 1 and the object I chose was the tape. The tape measure was about 24 inches long and the tape measure was placed on a slope. The starting time was 58.593. The three positions and the three corresponding clock times were as follows:
1st position: About 2 inches from the starting point (at the top of the slope), time is 59.25
2nd position: About 16 inches from the starting point, therefore the position is close to the middle of the slope, since 12 inches is the middle of the slope, time is 59.796
3rd position: About 24 inches from the starting point, therefore the position is at the very end of the slope, since the send of the slope is 24 inches, time is 60.015.
The difference between the starting time and the 1st position time is 59.25 – 58.593 = 0.657. The difference between the 1st position time and the 2nd position time is 59.796 – 59.25 = 0.546. The difference between the 2nd position time and the third position time is 60.015 – 59.796 = 0.219. This shows that the tape increases in speed as it is propelled down the slope
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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):
You could use the data to determine if the tape and/or pendulum are increasing or decreasing in speed as time increases. I think that if you did use observations of position and clock times from this video, you could determine the positions with some accuracy. You would give close and reliable estimates of the positions. There is a black mark on the measuring tape indicating where 1 foot is. The rest of the measuring tape is in inches. There are 12 inches in a foot and from the video you can see where each inch is on the measuring tape. Therefore, you can estimate how many inches the observed object is from the starting point. For instance, the first position of the tape that I observed was close to the 2 inch mark. I also looked at the time indicated on the clock when the tape hit the 2 inch mark. The second position of the tape that I observed was about 4 inches from the 1 foot marker, there are 12 inches in a foot, therefore the tape was positioned about 16 inches from the starting point. I once again looked at the time indicated on the clock when the tape hit the 16 inch mark. The time difference can show about how fast the tape was moving from the 1st position to the 2nd position. If you locate several positions and there corresponding times, you can determine if the object is speeding up or slowing down.
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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):
Based on the observed positions and the clock time associated with each position, you can determine whether the tape is speeding up or slowing down. For example, you record three different positions (marked 1 -3 as the tape rolls down the incline, 1 starting at the top, 2 toward the middle, 3 toward the bottom) and the corresponding times associated with each of those positions. Say the time difference between position 1 and position 2 is 0.234 and the time difference between position 2 and 3 is 0.034. Sine position on is located towards the starting point and position 3 towards the ending point and position 2 in the middle, it can be determined that the tape speeds up as it moves down the incline.
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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):
You can determine whether the swinging pendulum is speeding up or slowing down similar to how you can determine if the tape is speeding up or slowing down. Record three different positions (marked 1 – 3 as the pendulum is swung, 1 starting at the top, 2 toward the middle, 3 toward the end of the incline) and the corresponding times associated with each of those positions. If the difference between position 1 and position 2 is 0.234 and the time difference between position 2 and 3 is 0.034 then it can be determined that the swinging pendulum speeds up as it moves from the starting point to the ending point. If the difference between position 1 and position 2 is 0.034 and the time difference between position 2 and 3 is 0.234 then it can be determined that the swinging pendulum slows down as it moves from the starting point to the ending point.
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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):
Recording numerous positions and the corresponding times of the pendulum can help you determine when the pendulum is speeding up and when it is slowing down. If you record 9 different positions and their corresponding times (1 at the starting point and the rest are down the incline until the ending position is 9). The differences between the times between each position can show you if the pendulum is slowing down or speeding up.
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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 could take numerous observations of the position and corresponding time. You can record the time after every one inch the tape travels from the starting point, or every 2 inches, or every three inches, and so on just as long as you are recording the position after the same number of inches each time. If the difference in time between each position is the same then the tape is speeding up at a constant rate. If the difference in time between each position gets greater and greater between each position, moving from start to finish, then the tape is decreasing. If the difference in time between each position gets smaller and smaller between each position, moving from start to finish, then the tape is increasing.
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About 30 minutes
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