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course PHY 201
7/20 12 In the process of recovering files from one computer to submit labs.
Copy this document, from this point to the end, into a word processor or text editor.
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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 set up my experiment on a flat fold-out computer desk. I used my physics book (Giancoli's PHYSICS, ISBN: 0-13-184661-2) and the toy car that was included with the lab materials. I propped up the end of the book with two dominoes (from lab materials). The car rolled very smoothly and sped up as it rolled down the book cover.
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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:
Measurements taken with a ruler:
Distance traveled by car: 23.3 cm.
The propped up end of the book was 1.5 cm higher than the opposite end. Distance from the supports: 21 cm.
1st Set of Trials, Time Intervals when rolling to the left: 1.412, 1.221, 1.552, 1.502
2nd Set of Trials, Time Intervals when rolling to the right: 1.242, 1.201, 1.251, 1.172
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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:
In order to find velocity, I divided the distance traveled (23.3 cm) by the time taken to travel the distance (Time Intervals). I calculated the four different trials of each set (left and right), and then found the average by adding those eight values and dividing by eight.
Average speed of the car= 17.85 cm/s
The accuracy of this speed is questionable because of the potentiality for user error. It was such a short distance down the book and the height of the propped end caused the car to go faster. However, because I did eight trials and changed the direction of the slope, the value calculated for the average speed is a good representative of what happened.
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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 velocity of the car was 0 cm/s, because it started from rest. Therefore, the average speed during this interval can be found by taking the final velocity of the car (our average from above) and divide it by 2. Average speed during the interval should be 8.925 cm/s. I think that the car was moving at a speed much greater than the average speed that I just calculated when it reached the lower end of the book.
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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, and final speed & change in speed as it rolled from one end to the other are tied for greatest value.
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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:
For this experiment, I decided to create a situation where the distance traveled by the car was greater. I used a board that was 90 cm long and propped it up with a 5 cm thick book. I marked three areas of the board, 30 cm, 45 cm, and 60 cm. I had a friend help me with recording the timing of this experiment. She would watch the car roll down the board and tell me when it was passing the different marks (""1, 2, 3""). I used the timer program to record the time intervals between the three distances. By calculating (same as the earlier experiment) the speeds of the different intervals, we were able to observe that the fastest speed was observed during the 60 cm- 90 cm interval. We repeated the experiment three times to support our results.
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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?
50 minutes
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You may also include optional comments and/or questions.
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Revised: 30 May 2010 22:02:22 -0400"
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