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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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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:
I used our physics book sixth edition by giancoli. I used a rubber ball that is about the size of a gum ball. I propped a book up with one newspaper. The ball rolled very well speeding up and slowing down at a good rate. It took 1.76 seconds and about the same when I changed the direction. The direction changed somewhat.
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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:
It rolled 14.3 inches the first direction and 13.8 inches the second direction. I measured them with a ruler and I believe them to be accurate because I repeated the steps a few times and they were all around the same number.
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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:
14.3/1.76=8.125 in the first direction
13.8/1.66=8.313 in the second direction
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These calculations need to include units with every quantity that has units.
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I believe both to be accurate because I repeated the process several times and the numbers were pretty consistent.
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How fast was the object moving at the beginning of the timed interval? The ball started out slowly and then increased by speed and then decreased to a stop.
According to your previous calculation, what was its average speed during this interval? During the beginning interval, it was moving at around 5.326
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It isn't clear how this is related to your previous calculation.
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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? I believe it was moving at a faster speed when it reached the end of the book compared to the beginning.
your brief discussion/description/explanation:
when objects are launched from a slanted surface, it is typical that it will start out slow, speed up as it goes down the incline and then slow down once it is on a level surface again. This was the case in this experiment.
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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:
5.3
0
8.3
3.0
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These quantities need to be acompanied by the appropriate units.
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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 divided the book in half. When the ball reached the middle, I would start the timer for the bottom half and when I released the ball from the top of the book I would stop the timer once it got to the middle. The average speed was much faster towards the bottom then it was for the top. The average speed was about 1 second for the top half, and .7 for the bottom half.
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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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You need to take a few minutes and make some revisions. I don't think you'll find this difficult or time consuming, but if you have questions let me know.
&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes. &#
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