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PHY 241
Your 'initial timing experiment' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** Initial Timing Experiment_labelMessages **
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In the box below describe your setup, being as specific as possible about the book used (title, ISBN) and the object being used (e.g., a can
of vegetables (full or empty; should be specified) or a jar (again full or empty); anything round and smooth that will upon release roll
fairly slowly down the incline), and what you used to prop the object up (be as specific as possible). Also describe how well the object
rolled--did it roll smoothly, did it speed up and slow down, did it roll in a straight line or did its direction change somewhat?
your brief discussion/description/explanation:
I am using my copy of University Physics with Modern Physics, 13th edition, ISBN 13: 978-0-321-69686-1, ISBN 10: 0-321-69686-7. The book is
approximately 11 3/16 inches in length, the distance from the propped up end to the lower end measured along the table is 11.125 inches. The
object being rolled down the book is a nearly full (~90%) tube of chaptick, without the outer plastic wrapper. It is smooth, approximately
2.5 inches long, and roughly 5/8 in diameter. The book is propped up on a stack of two quarters under the approximate center on one end. The
tube seemed to roll smoothly and in a straight line down the face of the book.
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In the space indicated below report your data. State exactly what was measured, how it was measured, how accurately you believe it was
measured and of course what the measurements were. Try to organize your report so the reader can easily scan your data and identify any
patterns or trends.
your brief discussion/description/explanation:
Time is started when the tube is released at the higher propped-up end, and ends when it loses contact with the other end of the book after
rolling off. Initial value of t = t_0 = 0 seconds. Time will be measured as the interval from t_0 to the final time t_f using the TIMER
program. These measurements are likely accurate to within .1 seconds, based on observation.
Trial 1: t_f = 2.25 seconds
Trial 2: t_f = 2.356 seconds
Trial 3: t_f = 2.348 seconds
The following trials are recorded with the book being rotated 180 degrees.
Trial 4: t_f = 2.276
Trial 5: t_f = 2.334
Trial 6: t_f = 2.318
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Using your data determine how fast the object was moving, on the average, as it rolled down the incline. Estimate how accurately you believe
you were able to determine the object's average speed, and give the best reasons you can for your estimate of the accuracy.
your brief discussion/description/explanation:
t_ave = (2.25 + 2.356 + 2.348 + 2.276 + 2.334 + 2.318) / 6 = 2.313 seconds or about 2.3 seconds. Distacne rolled = s = 11.18 inches. v_ave = 11.18 / 2.3 = 4.8 inches / second
inches/second
I estimate that my time-recording was accurate to within .1 sec, considering the inherent flaws in the timer program, as well as the
inability as a human to make instantaneous actions. I believe that my measurement of the distance is likely accurate to within .05 inches or
so, judging by the inaccuracy of a simple ruler.
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How fast was the object moving at the beginning of the timed interval?
According to your previous calculation, what was its average speed during this interval?
Do you think the object, when it reached the lower end of the book, was moving at a speed greater or less than the average speed you
calculated?
your brief discussion/description/explanation:
The object started at a speed of v = 0 in/sec. Average speed over this interval was calculated as 4.8 inches / second. I believe that the
object was moving at a greater speed than calculated at the lower end of the book. This is because the average speed counts the earlier,
slower speeds in addition to the faster speeds towards the lower end of the book. Thus, the speeds towards the bottom must be faster than the
average in order to even out the slower speeds at the top.
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List the following in order, from least to greatest. Indicate 'ties': The object's initial speed, its final speed, its average speed, and
the change in its speed as it rolled from one end of the book to the other.
your brief discussion/description/explanation:
initial speed, average speed, tie for greatest: final speed & change in speed from one end to the other.
Initial speed is zero, final time must be greater than this, and tghus average time is between the two. The object gains speed from an
initial speed of zero until the end, so the change is the difference between final speed v_f and initial speed v_0. (Change in v) = v_f - v_0
= v_f - 0 = v_f.
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Devise and conduct an experiment to determine whether or not the object is speeding up as it rolls down the incline. If you have set the
experiment up as indicated, it should seem pretty obvious that the object is in fact speeding up. But figure out a way to use actual
measurements to support your belief.
Explain how you designed and conducted your experiment, give your data and explain how your data support your conclusions.
your brief discussion/description/explanation:
Time the object as it rolls down the book, doing as best as possible to record the time interval from the beginning to halfway down the book, marked with a piece of masking tape on the table, and then from that point to the end. See which average rate is greater. The frist interval will be recorded as t_1 and the second as t_2, both recorded in seconds.
Trial 1: t_1 = 1.7, t_2 = .60
Trial 2: t_1 = 1.65, t_2 = .61
Trial 3: t_1 = 1.82, t_2 = .54
Trial 4: t_1 = 1.67, t_2 = .63
The tube takes significantly less time to traverse the second half of the book than it does to roll down the first half from v = 0.
Thus, the tube is travelling faster the further down it rolls, so it is speeding up.
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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?
45 minutes
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You may also include optional comments and/or questions.
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&#Very good data and responses. Let me know if you have questions. &#