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course Phy 241
11/20/2012 815amI used the same format as your
Ball Rolling Down a Ramp
due to air resistance, density and acceleration of gravity. Data from this lab to is used to reach additional conclusions.
This lab should be completed in an hour.
Decohedron vs small dense object timing Experiment
The attachment shows two seperate dodecahedrons. Construct one or the other(be sure to note which one was used.) You will also need a ruler or
measuring tape and
your lab materials should also contain a marble, or some dice, or a large washer. The timer.exe program will also be used.
If a the two seperate objects are dropped from an initial state of rest at three varing heights, outstretched arm, height of table and knee high, do you think the difference in time between the two objects
will be greatest or least at the highest point. Explain why you think you have correctly predicted the behavior of the system.
Your answer (start in the next line):
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If we write down the times from least to greatest, next to the hieghts observed for each object, would you expect the time intervals
to be increasing or decreasing, or do you think there would be no clear pattern? Explain why you think you have correctly described
the behavior of the numbers in the table.
Your answer (start in the next line):
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Set up your experiment next to a table or a shelf. Using the measuring tape drop the decodeheron from a height of 6 feet, 4 feet and 2 feet.
Do the same thing with the small dense object. After going through the motions a few times to get the 'drift', go ahead and record the time
it took for each object to hit the ground with the timer.exe program. This is why you may need the shelf or table, so you can do the experiment safely.
Do 5 trials of the 'real' thing and record your time intervals with both the small dense object, first, and the decahedron, second.
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You can't time the drop with the TIMER program. There is an uncertainty of at least +- 0.1 second, and the human difficulty in triggering two events that close together would at least double that uncertainty.
Differences in drop time will only be around 0.1 second or so, so the uncertainty would practically obliterate the difference we are trying to observe.
I don't know about the dodecahedron, but from about 4 feet a loosely wadded piece of paper only beats a dense object, released at the same instant, to the floor by 10 cm or so. At the floor both objects would have been moving at about 5 m/s, so the difference in time is only about .02 second. That's just not observable in such a short interval with a human-triggered TIMER.
The method I used to get the .02 second difference, however, would be pretty accurate. The dense object will accelerate downward at 9.8 m/s^2 so we can calculate its final speed. From this and the distance by the less dense object lags it we can arrive at a reasonably accurate estimate of the time difference.
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If you wish you can also propose other methods of measuring the time difference. But the TIMER is just not an option here.
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In the space below, give the time interval for each trial, rounded to the nearest .001 second.
Give 1 trial on each line, so that you will have a total of 10 lines,
the first 5 lines for the first system(small dense object), then 5 lines for the second system(decohedron.)
Beginning in 11th line give a short narrative description of what your data means and how it was collected.
Also describe what you were thinking, relevant to physics and the experiment,
during the process of setting up the system and performing the trials.
Your answer (start in the next line):
List your intervals using the same format as before.
Your answer (start in the next line):
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You don't want to use my method for reporting data. I specify how the data is to be reported so I can later collect data over a large number of experiments. This particular experiment is unique. Your experimenter should report the results as a table with explanation of what was done and what the numbers in the table mean.
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Now measure the acceleration from the hieght of the outstretched arm to the tabletop. Obbtaining the time interval for each of 5 trials.
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The acceleration of the dodecahedron won't be uniform so you can't calculate its acceleration, at least not with the methods of this course.
What you could easily calculate would be the distance it dropped in the time it would have required to fall to the floor in the absence of air resistance (in which case its motion would have matched that of the dense object). If air resistance increases with speed, as we certainly expect, then this distance should increase in a way that reveals something about the nature of the increase. It can also answer the question of whether the dodecahedron reaches terminal velocity from this height, which was your original question.
Suggested control: drop two dense objects and see if they consistently hit the floor at the same time. If they don't adjust your method of releasing them until they do, then suggest this method to your experimenter, who should document his or her results with two dense objects. We need to know how much of the difference might be due to uncertainties in the simultaneity of the drops.
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Repeat the preceding using from the hieght of the outstretched arm to knee high. Enter your 5 time intervals using the same format as before.
Your answer (start in the next line):
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Good to here, with appropriate modifications.
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Do your results support or fail to support the hypotheses you stated in the first two questions, regarding the relationship between time intervals and slopes?
Explain.
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Your experimenter will not have formed hypotheses. The role of the experimenter is to get the data. The analysis and interpretation are left to other members of the team.
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Your answer (start in the next line):
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How do you think the average velocity of the ball is related to the hieght of the drop? Explain in as much detail as possible.
Your answer (start in the next line):
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Average velocities can certainly be calculated. This question, and those that follow, would be very appropriate to the interpreter. The analyzer would just calculate the various quantities, according to your requests.
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Speculate on what it is that causes the average velocity and acceleration
Your answer (start in the next line):
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How might you verify whether your speculations are indeed valid explanations?
Your answer (start in the next line):
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Does the height have a greater difference in velocity or the distance the object is allowed to drop have a greater impact on it's velocity?
Your answer (start in the next line):
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How does your data show that air resistance is a factor?
Your answer (start in the next line):
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Your instructor is trying to gauge the typical time spent by students on these experiments. Please answer the following question as accurately as you can, understanding that your answer will be used only for the stated purpose and has no bearing on your grades:
Approximately how long did it take you to complete this experiment?
Your answer (start in the next line):
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You don't need this instruction.
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Copy your document into the box below, be sure you have filled in your name and other identifying information at the top of this form, and submit:
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The data will probably be posted to Blackboard. The report could come to me, and I could do the posting; or we might have the various participants post results directly, perhaps via a discussion board.
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Good overall idea. You'll want to change the format a bit, and the TIMER is not a viable option, for reasons I detail. I suggest a different option, and you're free to suggest others.
Make appropriate revisions and send me a second draft.
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