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 used video 3 and focused on the pendulum.
11 inches at 29.343, 17 inches at 29.671, and 19 inches at 30.218
#$&*
In the following you don't have to actually do calculations with your actual data. Simply explain how you would use data of this
nature if you had a series of several position vs. clock time observations:
If you did use observations of positions and clock times from this video, how accurately do you think you could determine the
positions, and how accurately do you think you would know the clock times? Give a reasonable numerical answer to this question
(e.g., positions within 1 meter, within 2 centimeters, within 3 inches, etc; clock times within 3 seconds, or within .002 seconds,
or within .4 seconds, etc.). You should include an explanations of the basis for your estimate: Why did you make the estimate
you did?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
I think this data is fairly accurate because I paused the player and watched the video more than once to determine the
measurements. I'd say the measurement should be accurate within about 1/2 inch, just because when you do pause the tape, it is
blurry. Plus the pendulum is directly in front of the measuring tape so I can't get a perfect reading. The clock time was easy
to read when I paused the player, and I'm not sure about its accuracy, maybe .1 sec.
#$&*
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):
By having multiple measurements one can determine the speed of the item (distance per second) or whatever and can compare speed at
the top of the incline versus the speed near the bottom.
#$&*
How can you use observations of position and clock time to determine whether the swinging pendulum is speeding up or slowing down?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
One can evaluate the pendulum's positions based on a certain increment of time to determine if it is speeding up or slowing down.
For example, one may evaluate the position every .1 sec. If it has moved more than the last increment, we know that it is
speeding up. If it has moved less, it has slowed down.
#$&*
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):
#$&*
Challenge (University Physics students should attempt answer Challenge questions; Principles of Physics and General College
Physics may do so but it is optional for these students): How could you use your observations to determine whether the rate at
which the tape is speeding up is constant, increasing or decreasing?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
#$&*
Check to see that you have followed the instructions:
The instructions told you to pause the video multiple times. It appears that some students are not following this instruction.
If you haven't used the 'pause' and 'play' buttons on your media player, you should go back and do so.
The questions are phrased to ask not only what you see when you play the video, but what you see when you pause the video as
instructed, and what you think you could determine if you were to actually take data from the video. You aren't asked to actually
take the data, but you need to answer how you would use it if you did.
It's OK if you have given more general descriptions, which are certainly relevant. But answers to the questions should include an
explanation of how you could use the series of position and clock time observations that are may be observed with this video.
The questions also ask how much uncertainty there would be in the positions and clock times observable with this specific video.
Different people will have different answers, and some reasonable answers might vary from one clip to the next, or from one part
of a clip to another. However the answers should include a reasonable quantitative estimate (i.e., numbers to represent the
uncertainty; e.g., .004 seconds of uncertainty in clock times, 2 inches in position measurements. Use your own estimates; neither
of these example values is necessarily reasonable for this situation). You should also explain the basis for your estimate: why
did you make the estimate you did?
You should have estimated the number of seconds or fraction of a second to within which you think the time displayed on the
computer screen might be accurate (e.g., is it accurate to within 10 seconds of the actual clock time, or to within 1 second,
within .1 second, maybe even within .01 or .001 second). You might not yet know enough about the TIMER to give an accurate
answer, but give the best answer you can.
You should also indicate a reasonable estimate of the number of inches or fraction of an inch to within which you could, if asked,
determine the position of each object.
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About 25 min.
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I did skip the optional assign. at a Physic I student.
&#Good responses. Let me know if you have questions. &#