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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.
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Note: The majority of student report taking less than an hour on this experiment, though a few report significantly longer times.
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:
In the roughly 2 seconds it takes for the car to move from one end of the book to the opposite end, the car moves 28 cm. The car measured 7.5 cm long. The propped up in is 2 cm higher than the lower end. The diameter of the pencil I used was 1.5 cm. The total length of the book was 28.5 cm in length and 22 cm in width. The object started its decent slowly, but quickly gained speed as the slope increased and rolled in a straight line.
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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:
Start time Stop Time Difference in Time( in seconds)
2.653 4.203 1.55
11.584 13.414 1.83
18.974 21.034 2.06
The book I used as a ramp was the 6th edition Physics Giancoli textbook ISBN: 978013 0606204-JSBN.
To measure my lengths, I used a Lufkin 16’/5m x ¾’’ tape measure HY1035CME.
My prop was a number 2 pencil that had a 1.5 diameter. The car measured 7.5 cm long. The total length of the book I used was 28.5 cm in length and 22 cm in width. The propped up end is 2 cm higher than the lower end. I feel I measured very accurately. I tried to get as close as .1 of a cm.
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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:
I believe the speed of the object is 14 cm a second. This is supported by the fact that the entire trip takes roughly 2 seconds and the entire length of the book is 28 cm. If you work to find speed, which you are able to do because you know distance and time, then you have 28cm=s*2 seconds => s=14 cm/second. Therefore the car would have to move 14 cm/sec to cover 28 cm in 2 seconds.
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Good.
This isn't necessary on this experiment, but so note for future reference that this is the average speed. The object also has an intial speed and a final speed. The initial speed is zero, so the final speed must be greater than the average speed. For that reason it's a good idea never to use either of the terms 'speed' or 'velocity' without an adjective. So for example you would use the more specific terms like 'initial velocity' or 'final velocity' or 'average velocity' or 'instantaneous velocity' or 'change in velocity', rather than just 'velocity'.
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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:
At the beginning of the times interval, the object was traveling maybe 1cm in 1/64 seconds. I believe the objet was moving at a greater speed than I calculated based on the consistency of the slope.
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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:
Object’s initial speed (starting speed is smaller than all)
Change in speed (speed is greater because of the slope)
Average speed (greater than previous since the slope is constant and constantly)
Final speed (Greatest speed because it is the last speed as the slope is the greatest)
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You would expect the average speed in this situation to be between the initial and final speeds. The speed is steadily increasing, and the initial speed is clearly less than the average speed, so the final speed has to be greater than the average.
The initial speed being zero, the change in speed would just be the final speed.
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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:
Pencil used was 1/5 cm diameter. This pencil was my prop that held up my Physics I text book on one end. The pencil caused the higher end to be 2 cm higher than the lower end. The book was 28.5cm in length and 22 cm in width. I used a small toy car (it wasn’t included with the initial lab package). The car was 7.5 cm in length. The car rolled down the book in approximately 2 seconds. I tested the experiment 3 times with the pencil propping up one end.
These were the measurements of time it took for the car to roll from the higher end to the lower end.:
Start time Stop Time Difference in Time ( in seconds)
2.653 4.203 1.55
11.584 13.414 1.83
18.974 21.034 2.06
I also timed the amount that it took the car to reach from one end to the other, if the higher end became the lower end. I did this as a way to verify the measurements. The time measurements were:
Start time Stop Time Difference in Time ( in seconds)
3483.325 3485.898 2.573
3492.911 3495.811 2.9
3500.483 3503.073 2.59
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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?
This experiment took me an hour and a half.
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You may also include optional comments and/or questions.
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Please copy your document into the box below and submit.
#$&* self-critique
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Good work. Do be sure, though, to see my notes. They will be helpful in upcoming assignments. If you have questions on my notes or anything else about this experiment, lbe sure to et me know.
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