course Phy 232
6/19/09, 4:00
ph2 query 0Most queries in this course will ask you questions about class notes, readings, text problems and experiments. Since the first two assignments have been lab-related, the first two queries are related to the those exercises. While the remaining queries in this course are in question-answer format, the first two will be in the form of open-ended questions. Interpret these questions and answer them as best you can.
Answer: This is the first assignment, there have been no other assignments before this one.
Different first-semester courses address the issues of experimental precision, experimental error, reporting of results and analysis in different ways and at different levels. One purpose of these initial lab exercises is to familiarize your instructor with your work and you with the instructor 's expectations.
Comment on your experience with the three lab exercises you encountered in this assignment or in recent assignments.
There haven’t been any lab assignments.
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Question: This question, related to the use of the TIMER program in an experimental situation, is posed in terms of a familiar first-semester system.
Suppose you use a computer timer to time a steel ball 1 inch in diameter rolling down a straight wooden incline about 50 cm long. If the computer timer indicates that on five trials the times of an object down an incline are 2.42sec, 2.56 sec, 2.38 sec, 2.47 sec and 2.31 sec, then to what extent do you think the discrepancies could be explained by each of the following:
• The lack of precision of the TIMER program.
To what extent to you think the discrepancies are explained by this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv I don’t think the lack of precision of the TIMER program has anything to do with the discrepancies in the times. The recorded times are only recorded to 2 decimal points. The TIMER program is accurate to something like 5 decimal points.
• The uncertain precision of human triggering (uncertainty associated with an actual human finger on a computer mouse)
To what extent to you think the discrepancies are explained by this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv This could shed or add a millisecond from each trial because the human might not have pressed the mouse right on. It could have been hit to the side of the button which would make the time very slightly larger than it would have been hit in the middle of the mouse button.
• Actual differences in the time required for the object to travel the same distance.
To what extent to you think the discrepancies are explained by this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv I don’t think this has anything to do with the discrepancies in times, maybe if there was wind for a couple of trials the time would change, but the experiment was probably done indoors.
• Differences in positioning the object prior to release.
To what extent to you think the discrepancies are explained by this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv This is a big reason for the discrepancies in times. It’s very difficult to put the ball in the exact same starting position with no momentum either way for each trial. This could account for several hundredth second differences in the trials.
• Human uncertainty in observing exactly when the object reached the end of the incline.
To what extent to you think the discrepancies are explained by this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv It is almost impossible to tell when exactly the ball reaches the end of the incline. I’m surprised the trials were that close in time even with this obstacle. Also the human might not be looking at the ball from the same angle each trial. This fluctuates the times greatly.
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Question: How much uncertainty do you think each of the following would actually contribute to the uncertainty in timing a number of trials for the ball-down-an-incline lab?
• The lack of precision of the TIMER program.
To what extent to you think this factor would contribute to the uncertainty?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv The TIMER program is very precise. The program if I remember it correctly is accurate to something like 6 decimal places. The human clicking the TIMER button is probably the one to blame for the discrepancies. Maybe the human looked at the ball from different angles as it finished its decline or maybe the initial release of the ball was not consistent.
• The uncertain precision of human triggering (uncertainty associated with an actual human finger on a computer mouse)
To what extent to you think this factor would contribute to the uncertainty?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv I think the precision of human triggering is one reason for the discrepancy in each trial. Maybe the computer mouse was harder to click than a previous time. Or maybe the human didn’t press the button square on in some trials but did for others.
• Actual differences in the time required for the object to travel the same distance.
To what extent to you think this factor would contribute to the uncertainty?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv There might be a very slight difference in time because of this but I don’t think we could tell the difference to the nearest hundredth of a second as we are doing with each trial.
• Differences in positioning the object prior to release.
To what extent to you think this factor would contribute to the uncertainty?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv The difference in ds is another big reason the times are slightly different. Maybe the human didn’t place the ball at the very top of the ramp for some trials but did for others. Or when the human released the ball, the human didn’t release the ball impartial to the velocity going up or down the ramp. It’s nearly impossible to release the ball perfectly motionless on an incline.
• Human uncertainty in observing exactly when the object reached the end of the incline.
To what extent to you think this factor would contribute to the uncertainty?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv I think this is the major reason for the discrepancy in time for each trial. The human may not be looking at the end of the incline from the same angle each time.
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Question: What, if anything, could you do about the uncertainty due to each of the following? Address each specifically.
• The lack of precision of the TIMER program.
What do you think you could do about the uncertainty due to this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv TIMER program is very accurate, even if it wasn’t can’t do anything to change it.
• The uncertain precision of human triggering (uncertainty associated with an actual human finger on a computer mouse)
What do you think you could do about the uncertainty due to this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv If we make sure we are hitting the mouse button to start and stop the trial in the middle of the button we could eliminate any discrepancies caused by the human triggering.
• Actual differences in the time required for the object to travel the same distance.
What do you think you could do about the uncertainty due to this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv We could just make sure there’s no wind by doing the experiment indoors. Other than that there’s not going to be many discrepancies caused by this.
• Differences in positioning the object prior to release.
What do you think you could do about the uncertainty due to this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv If we have some mechanical starting tool that allows us to set the ball in the same position each time we could eliminate any problems with this issue.
• Human uncertainty in observing exactly when the object reached the end of the incline.
What do you think you could do about the uncertainty due to this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv If we look at the ball as it rolls off the incline at the same angle each time, it would greatly help.
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&#Your work looks good. Let me know if you have any questions. &#