Phy 201
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 the pendulum in video 4. The first clock time was 20.562 and its position at that point was approximately at the 6 in. mark. The second clock time was 20.890 and its position at that point was approximately at the 15 in. mark. The third clock time was 21.209 and its position at that point was approximately at the 21 in. mark.
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 any explanations of the basis for your estimate: Why did you make the estimate you did?
answer/question/discussion: The timer seems to be accurate within .1 seconds of actual clock time and the position seems to be accurate within 1 in. of an actual measurement. If you were to look at the position of your object at say the 6 in. mark and the timer at that point read 10 seconds that you should be able to determine that for every 6 in. your object moves it should move at a rate of about 10 seconds. This would be only in the case of constant movement though which seems to be how the pendulum moves. That is why I think it is reasonable to make this estimate.
• 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: As the tape rolls down the ramp it appears to roll faster because when you look at the clock compared to position the clock time as compared to the position do not change at a constant rate. The speed is increasing at an increasing rate because for each position that the tape moves to along the incline it takes less time to traveler a greater distance the further it rolls.
• 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: If the pendulum was speeding up or slowing down you could look at the position it was in, say at the 4 in. mark, then look at it again 4 in. from its original position and see if it too the same amount of time to get there as the previous trial, more time than the previous trial, or less time than the previous trial.
• 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:
• 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: You could determine this by looking at its position at a given point on the ramp and then as it approach the next appropriate point in correspondence to the original point and then so on down the ramp, you could compare the time intervals between each and determine if they were getting larger, smaller, or staying the same.
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30 minutes
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&#Good responses. See my notes and let me know if you have questions. &#