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course Phy 242
June 6 around 9:20 am
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.
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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 When using the timer program it became apparent that the program could only calculate time in certain increments. The full seconds themselves were accurate, but the decimals following had a set incremental change. For example (this isn't necessarily the increments of the program), if the timer program recorded 1.05 and 1.10 for the same occurence, I could suggest that perhaps the second decimal place is recorded in increments of .05. However, in this particular case these numbers are given with only two decimal places. And if I'm remembering correctly, the TIMER program had increments starting in the third decimal place. I don't think the discrepancies are explained by this factor. Although it isn't the most precise timing program out there, these numbers aren't incredibly precise and therefore I don't believe the TIMER program has much to do with their discrepancies.
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· 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 I think this could be a factor that would cause the numbers to be slightly off. This would explain numbers varying by as much as .16 seconds. I think this could be a huge factor in the discrepancies of the numbers.
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· 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 If the surroundings were the same for each trial, I don't think there should be much variance in the amount of time to travel. But these numbers don't vary by a whole lot so some of the variance could be due to this.
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· 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 could have a pretty big effect on the time it takes. For example, if the steel ball is positioned just a tad further up the incline, then it would probably take just a tad longer for it to reach the bottom of the incline. And if it's placed just a little further down on the incline, it would most likely get down in the incline in a tiny bit shorter of a time.
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· 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 This could easily explain the discrepancies. Again, I wouldn't expect the variance to be off by more than half a second but this very well could be a cause of the variance in the numbers of each trial.
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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 I think this contributes a little to the uncertainty. If the TIMER program is using rounded numbers, you would have to wonder if that's what is causing a variance in recorded times.
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· 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 this has some to do with the uncertainty. However, I don't think this has a whole lot to do with the uncertainty because I don't think it's that hard to make two things happen at the same time (release the ball and click the mouse). Also, unlike stopping the time when the ball reaches the end of the incline, someone is under full control of releasing the ball. Therefore, as long as the two people (or one individual) can count to three and then do their individual clicks and releases, this shouldn't lead to much uncertainty.
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· 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 I think this contributes some to the uncertainty. But not by a whole lot, because it's not like the amount of friction (if it's changing) would affect the times by a lot. Since the times don't vary by very much though, this very well could contribute to the uncertainty.
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· Differences in positioning the object prior to release.
To what extent to you think this factor would contribute to the uncertainty?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv I don't think this is a huge contribution to the uncertainty simply because even if the person releasing the ball is eyeballing it, I wouldn't think they would be off by that much for it to really matter much in the timing.
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· 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 would contribute a little bit to the uncertainty.
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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 I'm not sure that there's much to do other than perhaps use a different program to have a more precise time.
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· 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 Like I said about the stop time, it would be cool to use a program with some sort of automated start time. Perhaps a motion sensor that could detect when the ball starts rolling. Again, this sounds pretty complicated so a simpler way to correct this error a little would be to have a separate person triggering the computer mouse so that this is their main focus.
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· 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 For this, I don't think there is a whole lot you can do. If you really wanted to control this, a frictionless surface would be ideal. Different parts of the incline could have more or less friction. And if the ball rolls over an area with more friction, this could increase the amount of time it takes to roll down. If the ball rolls over an area with less friction, this could decrease the amount of time it takes to roll down. However, even with a frictionless surface I still think there will be some variance (probably not enough to really matter).
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· 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 For this, I would tape a very small string or piece of thread around the area I want to start from, that way I'm not just having to eyeball where the starting position is.
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· 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 Perhaps use a different program. One that had a motion sensor that could stop the time when the ball reached the end of the incline. To me that sounds pretty advanced so a more simple solution could be to have someone else stop the time so that their full focus can be on making sure they stop the time at the correct spot.
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Motion sensors aren't particularly accurate, but in many situations they are more accurate than human-triggered timers.
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Very good thinking, good ideas.
Check my one note.
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