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Phy 201
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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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 used was our physics textbook by Giancoli, and the object rolling down the book propped up by 3 quarters was the Hotweels car in the lab package. The car rolled smoothly; however, at times it would veer off to one side and I would have to repeat the measurement.
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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:
Trial Times set 1 Times set 2 (book rotated 180 degrees)
1 1.847 s 2.39 s
2 2.983 s 1.97 s
3 2.01 s 2.64
4 1.88 s 2.19
Avg: 2.18 s Avg: 2.30 s
Distance = 0.35 m
The average time for the car to roll down the 0.35 meter inclined plane was 2.18 seconds, which is fairly consistent with expected results. However, the measurements varied between trials, which suggests experimental error due to human reaction time.
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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:
Average velocity 1 = 0.35 m / 2.18 s = 0.161 m/s
Average velocity 2 = 0.35 m / 2.30 s = 0.152 m/s
When the book was rotated 180 degrees, the time increased slightly, thereby lowering the average velocity. It is unclear what produced this variation, but there is no reason to believe rotating the surface would influence the velocity of the object traveling down it. However, the velocities for each trial were relatively close, indicating that measurements were reasonably accurate.
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How fast was the object moving at the beginning of the timed interval?
The initial velocity was 0 becuase the object started at rest.
According to your previous calculation, what was its average speed during this interval?
Average velocity 1 = 0.35 m / 2.18 s = 0.161 m/s
Average velocity 2 (rotated 180 degrees) = 0.35 m / 2.30 s = 0.152 m/s
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:
It was moving at a speed greater than the average speed. Our formulas tell us that in an ideal situation the object will be moving at double its average velocity when it reaches the bottom of the ramp. Final velocity = 2(average velocity)
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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 (tied with change in speed) < final speed
Since the final speed should equal 2* the average speed, the change in speed should be equal to the average 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:
You could devise a similar experiment where mulitple time measurements are taken as the object reaches various marked points on a larger inclined plane. This would enable you to trace the change in velocity and calculate the acceleration of the object as it moves down the ramp. You will observe the object speeding up, and you could even have an object traveling at a known speed moving down the inclined plane next to it to use as a baseline for comparison.
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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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&#Very good data and responses. Let me know if you have questions. &#