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Phy 121
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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Take reasonable care to get good data in this experiment. Try to do the timing as accurately as possible. Measurements of length, height, etc. should be reasonably accurate (e.g., with a meter stick or ruler you can measure to withing +- 1 millimeter, but it's not necessary to try to determine fractions of a millimeter).
In this experiment you will use the TIMER program, a hardcover book, the toy car that came in your lab materials package (or, if you do not yet have the package, a cylinder or some other object that will roll along the book in a relatively straight line), and a ruler or the equivalent (if you don't have one, note the Rulers link, which is also given on the Assignments page).
• The book's cover should be straight and unbent.
• The toy car (or other object) should roll fairly smoothly.
Place the book on a flat level tabletop. You will prop one end of the book up a little bit, so that when it is released the object will roll without your assistance, gradually speeding up, from the propped-up end to the lower end. However don't prop the end up too much. It should take at least two seconds for the ball to roll down the length of the book when it is released from rest. For a typical book, a stack of two or three quarters placed under one end works well.
• Using the TIMER program determine how long it takes the ball to roll from one end of the ramp to the other, when released from rest. Once you've got the book set up, it takes only a few seconds to do a timing, so it won't take you long to time the object's motion at least three times.
• Determine how far the object travels as it rolls from its initial position (where you first click the timer) to its final position (where you click at the end of the interval). This will probably be a bit less than the length of the book, due to the length of the object itself.
• Determine how much higher one end of the book was than the other, and how far it is from the supports (e.g., the stack of quarters, or whatever you used to support one end) to the end of the book which rests on the table.
Then reverse the direction of the book on the tabletop, rotating the book an its supports (e.g., the stack of quarters) 180 degrees so that the ball will roll in exactly the opposite direction. Repeat your measurements.
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:
The book title Human Physiology- From Cells to Systems (ISBN: 978-1-111-57743-8), the book end to end was 28 cm. The can traveled 27.5 cm from end to end.
I used a Natures Promise Black Beans full can, and the book was propped up by 3 Canadian quarters. The can rolled fairly smooth, it stayed relatively in a straight line as well. The can seemed to go faster as it traveled towards the end.
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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:
I measured the time it took for the can of beans to get form one point of the book to the end of the book. I propped one end of the book up with 3 Canadian quarters. I started the can rolling on the side with the quarters. I believe my measurements were pretty accurate, there more than likely is human error. I could have not clicked the timer at the exact start and end time making the results off slightly off.
Canadian Quarters at the top of the book near the book description-Left to Right:
Trial 1:
Start Time: 2.74 End Time: 6.813
Total Time Rolled: 4.073 seconds
Trial 2:
Start Time: 1.164 End Time: 4.658
Total Time Rolled: 3.494 seconds
Trial 3:
Start Time: 2.164 End Time: 5.773
Total Time Rolled: 3.609 seconds
Canadian Quarters at the bottom of the book near the ISBN-Right to Left:
Trial 1:
Start Time: 2.11 End Time: 5.985
Total Time Rolled: 3.875 seconds
Trial 2:
Start Time: 1.542 End Time: 5.335
Total Time Rolled: 3.793 seconds
Trial 3:
Start Time: 1.114 End Time: 4.695
Total Time Rolled: 3.581 seconds
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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:
Moving from Right to Left the ball averaged 3.72 seconds to travel down the incline. So its average speed is 7.39 cm/sec. (I divided the cm traveled by the average seconds)
Moving from Left to right the ball averaged 3.75 seconds to travel down the incline. So its average speed is 7.33 cm/sec.
(I divided the cm traveled by the average seconds)
I believe my measurements are accurate within 0.5-1.0cm/sec. Like I said earlier since I am starting and stopping the clock there is no way that I can precisely start and stop the timer at the exact moment that I start and stop the can.
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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:
I took the total length traveled by the can and divided it by the beginning time. (27.5 cm/ 2.74 seconds=10.0) Therefore, the object was moving 10.2 cm/sec.
I averaged the three trials I completed with the can rolling from left to right. ([10.0 cm/sec+23.6 cm/sec+12.7 cm/sec]/3= 15.43 cm/sec.
???? Not sure why but my trial 2 was moving a lot faster then Trial 1 and 3. I think that threw off my average of the three trials.
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The contents of the can will shift, and this probably accounts for the significant deviation in the required times.
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Since the can started from a rest position, it was slower in the beginning and sped up as it moved down the incline. When the car reached the lower end of the book it was traveling at a greater speed then the beginning average.
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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- will be the slowest since it must pick up momentum to go, and it started at a rest position
Change in Speed- greater than the average because you are subtracting the initial speed from the final speed where as in the average you would just take the mean of the trials.
Average Speed
Final Speed- after picking up momentum this would be the fastest.
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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:
I took the time at three places, rather than one in the original experiment. I marked off the middle of the book and timed there as well as the beginning and the end of the book. I compared the first and second measurements to determine if the can was increasing speed.
From beginning to middle to end:
Trial 1: 1.925 seconds to 3.323 seconds then finally to 4.48 seconds
From beginning to middle: 1.398 seconds
From middle to end: 1.157 seconds
Trial 2: 2.095 seconds to 3.985 seconds then finally to 5.212 seconds
From beginning to middle: 1.89 seconds
From middle to end: 1.23 seconds
Trial 3: 2.550 seconds to 3.989 seconds then finally to 5.282 seconds
From beginning to middle: 1.439 seconds
From middle to end: 1.293 seconds
The first measurement was longer than the second measurement, therefore I can conclude that the can was in fact 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?
1 hour
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You may also include optional comments and/or questions.
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&#Good responses on this lab exercise. See my notes and let me know if you have questions.
Revision isn't requested, but if you do choose to submit revisions, clarifications or questions, please insert them into a copy of this document, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
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