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PHY 231
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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6:25
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:
Instead of a book, I used a VCR cassette which has a paper/cardbox cover on it. I could not find a toy card within my lab materials, so I used a marble which was included with the lab equipments. Instead of doing this experiment on the table, I performed this experiment on the floor. Instead of using quarters, to raise the VCR cassette, I used a single domino which was included with lab equipment.
While the marble is on the VCR cassette, it might change the angle a little but not too much. It manages to roll off the VCR cassette on the opposite end, not on the sides. Once it rolls off on the hardwood floor, it rolls straight.
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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:
(The first three numbers are in one direction and the next three numbers are in opposite direction).
Height of the initial position: 3.2 cm
Distance traveled on elevated surface: 18.8 cm
Total boards traveled: 20, 18, 15, 21, 19, 24 (each board is 5.7 cm)
Total distance (cm) traveled: 114, 102.6, 85.5, 119.7, 108.3, 136.8 (each board is 5.7 cm)
Seconds from top of VCR until the ball stopped: 6.5, 7.0, 7.8, 8.3, 7.1, 8.4
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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:
cm/ second, 114/6.5 = 17.5, 102.6,/7.0 = 14.7, 85.5/7.8 = 11.0, 119.7/8.3 = 14.4, 108.3/7.1 = 15.3, 136.8/8.4 = 16.3
I am not sure sure on the accuracy, since when I performed the experiment, the ball rolled in one direction. At the very very end before coming to a complete stop, it sometimes would roll in circles, sometimes backwards, sometimes sideways.
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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 very beginning, the initial speed was 0cm per second. The speed increased until marble reached the end of the VCR cassette and touched the floor. At this point, the speed was the greatest. As the ball rolled on the floor, the speed gradually decreased.
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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:
Marble's initial speed = its final speed (when it stopped rolling) = 0cm/sec, its average speed, the change in its speed as it rolled from one end of the book to the other = fastest speed in which it rolled.
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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 would conduct the exact same experiment, except this time, I would video-tape it. Then I would analyze the video, frame by frame, and could prove that the object is indeed speeding up as it rolls down the incline.
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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?
Around fifty minutes
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You may also include optional comments and/or questions.
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The instructions said to time the ball from one end of the ramp to the other. Your time included time spent rolliing on the floor.
You reported your information very well.
However the point of timing the ball from one end of the ramp to the other was that this would be an interval during which acceleration is constant.
The acceleration on the ramp is in the same direction as the motion of the ball, while the acceleration on the floor is mostly opposite the motion, and apparently (since the ball didn't follow a straight path on the floor) sometimes with a nonzero component perpendicular to the motion.
It's fairly easy to analyze uniformly accelerated motion. It's more challenging to analyze nonuniformly accelerated motion.
So while you have data you can't easily analyze at this point of the course, you've hopefully learned that there is an important distinction between uniformly accelerated motion and nonuniformly accelerated motion.
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