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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:
The book I used was my physics text book, whose ISBN is 0-13-060620-0. My supports consisted of five United States quarters at two of the corners of the top of the book. I used the car supplied in the kit. In most every run, it ran smoothly as it sped up to the end of the book. Only once did it go at an angle instead of 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:
1st roll-2.347656 seconds
2nd roll-2.101563
3rd roll-2.089844
distance (length that it rolled)-28.2 cm (11 1/8 inch)
height off table- 1 cm
side with supports: 4.5 cm
side without: 3.5 cm
reverse (180 degree switch):
1st roll- 1.960938
2nd roll-2.589844
3rd roll-1.910156
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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:
On the first run, the average time was 2.179687. The second run, the average time was 2.153646.
First run : 28.2 cm/ 2.179687= 12.9376 cm/second
Second run: 28.2/ 2.153646= 13.09407 cm/ second
Combined run: 28.2/ 2.1666= 13.01578 cm/ second
I have a 90% confidence level that the answers are accurate. The surface of the book, accuracy of the timer, and human error contributes to the 10% uncertainty.
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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:
The initial speed was zero since I started it at the edge of the length. In the first run it took it 2.179687 seconds to travel the 28.2 centimeters giving its a speed of 12.9376 cm/ second. I believe it was going faster , because the incline would allow for gravity to inact on it. There was also nothing to to stop the car.
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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:
The initial speed was zero. The average speed and change in speed was about 13 cm/ second. Its final speed would be slightly higher.
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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 reset the experiment and this time took a time when it hit about midway down the book. From the top of the book to midway, it took 1.460938 seconds. From midway to the bottom, it took 1.238281.
Top to midway: 14.1cm/ 1.460938= 9.65133 cm/ second
midway to bottom: 14.1 cm/ 1.238281= 11.38675 cm/ second
Conclusion, I proved my theory by finding that the velocity is higher from midway to the bottom of the book.
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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?
#$&* It took about 45 minutes.
You may also include optional comments and/or questions.
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*#&!
&#This looks very good. Let me know if you have any questions. &#