course PHY202 • µ¸ü°ãTˆ á·›Î⎎–׸è‘assignment #000
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10:17:40 Different first-semester courses addressed 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 instuctor with your work and you withthe instructor 's expectations. {}{}Comment on your experience with the three lab exercises you encountered in this assignment.
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RESPONSE --> The three lab exercises refreshed my memory on error analysis and precision. Although I was familiar with the mean and standard deviation, I learned more about the normal distribution about the mean.
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10:26:41 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 asteel 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: {}{}a. The lack of precision of the TIMER program{}{}b. The uncertain precision of human triggering (uncertainty associated with an actual human finger on a computer mouse){}{}c. Actual differences in the time required for the object to travel the same distance.{}{}d. Differences in positioning the object prior to release.{}{}e. Human uncertainty in observing exactly when the object reached the end of the incline.
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RESPONSE --> A. The Timer program is only precise to the nearest tenth of a second. B. There is some uncertainty in the precision of the human trigger. Probably within 0.5 sec. C. There is probably very little difference in the time for the object to travel the same distance each time. I would estimate +/-0.001sec. D. I would say the object is positioned within +/-0.0001cm of the same position each time. E. I would say there is probably +/-0.05sec of uncertainty for the human observing the object reaching the end of the incline. confidence assessment: 3
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10:28:27 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? {}{}a. The lack ofprecision of the TIMER program{}{}b. The uncertain precision of human triggering (uncertainty associated with an actual human finger on a computer mouse){}{}c. Actual differencesin the time required for the object to travel the same distance.{}{}d. Differences in positioning the object prior to release.{}{}e. Human uncertainty in observing exactly when the object reached the end of the incline.
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RESPONSE --> A. +/-0.1sec B. +/-0.05sec C +/-0.001sec D. +/-0.001cm E. +/-0.001sec confidence assessment: 3
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10:33:20 What, if anything, could you do about the uncertainty due to each of the following? Address each specifically. {}{}a. The lack of precision of the TIMER program{}{}b. The uncertainprecision of human triggering (uncertainty associated with an actual human finger on a computer mouse){}{}c. Actual differences in the time required for the object to travel the same distance.{}{}d. Differences in positioning the object prior to release.{}{}e. Humanuncertainty in observing exactly when the object reached the end of the incline.
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RESPONSE --> A. Nothing can be done. B. Design a mechanical setup that triggers the start and stop time to remove human error. C. Nothing. D. Design a mechanical device in which to insert the object. E. Use a video camera and mechanical trigger. confidence assessment: 3
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Ðþ•Öx^Ž®G Ü|«nõ÷å•f}’¥xº”Æ¿™û assignment #001 001. Physics II 09-07-2008
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23:24:19 Most queries in this course will ask you questions about class notes, readings, text problems and experiments. Since the first two assignments have been experiments, the first two queries are related to the experiments. 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.
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RESPONSE --> ok
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assignment #001 001. Physics II 09-08-2008
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19:06:08 Most queries in this course will ask you questions about class notes, readings, text problems and experiments. Since the first two assignments have been experiments, the first two queries are related to the experiments. 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.
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RESPONSE --> ok
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19:10:02 Suppose you measure the length of a pencil. You use both a triply-reduced ruler and the original ruler itself, and you make your measurements accurate to the smallest mark on each. You then multiply the reading on the triply-reduced ruler by the appropriate scale factor. Which result is likely to be closer to the actual length of the pencil? What factors do you have to consider in order to answer this question and how do they weigh into your final answer?
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RESPONSE --> The result from the ruler is likely to be closer to the actual length of the pencil. I have to take note of the factors of the accuracy of each measurement instrument used. The ruler is accurate to 1 mm. The triply reduced ruler more than likely has some optic distortion that would make the measurement less accurate. Therefore I would consider the real ruler to be more accurate. confidence assessment: 3
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19:13:28 Suppose you are to measure the length of a rubber band whose original length is around 10 cm, measuring once while the rubber band supports the weight of a small apple and again when it supports the weight of two small apples. You are asked to report as accurately as possible the difference in the two lengths, which is somewhere between 1 cm and 2 cm. You have available the singly-reduced copy and the triply-reduced copy, and your data from the optical distortion experiment. Which ruler will be likely to give you the more accurate difference in the lengths? Explain what factors you considered and how they influence your final answer.
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RESPONSE --> I would say that the triply reduced ruler would be more accurate when it does not have optical distortion because it leaves less room for uncertainty with its accuracy to 4 significant figures. I believe that the singly reduced copy will give more accurate results because it had less optical distortion than the triply reduced ruler. confidence assessment: 3
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19:33:57 Later in the course you will observe how the depth of water in a uniform cylinder changes as a function of time, when water flows from a hole near the bottom of the cylinder. Suppose these measurements are made by taping a triply-reduced ruler to the side of a transparent cylinder, and observing the depth of the water at regular 3-second intervals. {}{}The resulting data would consist of a table of water depth vs. clock times, with clock times 0, 3, 6, 9, 12, ... seconds. As depth decreases the water flows from the hole more and more slowly, so the depth changes less and less quickly with respect to clock time. {}{}Experimental uncertainties would occur due to the optical distortion of the copied rulers, due to the the spacing between marks on the rulers, due to limitations on your ability to read the ruler (your eyes are only so good), due to timing errors, and due to other possible factors. {}{}Suppose that depth changes vary from 5 cm to 2 cm over the first six 3-second intervals. {}{}Assume also that the timing was very precise, so that there were no significant uncertainties due to timing. Based on what you have learned in experiments done in Assignments 0 and 1, without doing extensive mathematical analysis, estimate how much uncertainty would be expected in the observed depths, and briefly explain the basis for your estimates. Speculate also on how much uncertainty would result in first-difference calculations done with the depth vs. clock time data, and how much in second-difference calculations. {}{}How would these uncertainties affect a graph of first difference vs. midpoint clock time, and on a graph of second difference vs. midpoint clock time? {}How reliably do you think the first-difference graph would predict the actual behavior of the first difference? {}Answer the same for the second-difference graph. {}{}What do you think the first difference tells you about the system? What about the second difference?
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RESPONSE --> I would say the uncertainty would be +/-2.12cm because that it the estimated standard deviaiton. There would be more uncertainty with the first difference calculations than with the original data. There would be even more uncertainty with the second difference calculations than with the first difference calculations. These uncertainties would be somewhat visible in the first difference graph as it might be difficult to determine where to place the best fit line. The uncertainties would be more visible in the second difference graph because a clear trend would not be visible. The first difference graph is some what reliable but not completely reliable for predicting the behavior of a system ( you can see a trend). The second difference graph is not reliable for predicting the behavior of the system. The first difference graph tells you the average velocity of the object. The second difference graph tells you the average acceleration. confidence assessment: 3
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¥ô¢¤¹Í}Ú´ç¸|õUè§õáüÈ assignment #001 001. Physics II 09-08-2008