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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.
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02/10 12:00
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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:
In order to conduct this experiment, I used an Astronomy Textbook (ISBN: 0-07-248262-1) that was 285 mm in length and 27 mm thick. The object that I used was a 110 mm tall, 10 ounce full can of Rotel Original Diced Tomatoes & Green Chilies.
I used 3 quarters and 3 nickels (total 10 mm thick) to prop up one end of the book. The distance from the prop (3 quarters & 3 nickels) to the other end of the book was 272 mm. The elevated end of the book was 38 mm high while the other end of the book was 29 mm high. The distance from where the object started (initial click) to where it ended (final click) was 230 mm.
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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:
In my experiment, I measured the time it took for the Rotel can to roll from one mark on the book to another (230 mm distance). To conduct the time experiment, I would place the can in the proper place. As soon as I let go of the can, I began the timer and when it crossed the end point on the book, I clicked the timer again to get the time interval.
I believe that my measurements are fairly accurate given the situation and tools. It is somewhat difficult to be precisely right each time by just looking and clicking when the object crosses a certain point. In a lab this experiment could be performed with more accuracy and precision, but I believe I done ok given what I have.
My time interval measurements for the can going from right to left, and then left to right and reported below:
The following is the time intervals (from starting click to end click) for three different trial runs with the object rolling from my right to my left:
Trial 1: 2.507813 seconds
Trial 2: 2.539063 seconds
Trial 3: 2.480469 seconds
The next set of date is time intervals (from starting click to end click) for three different trials runs with the object rolling from my left to my right:
Trial 1: 2.500000 seconds
Trial 2: 2.480469 seconds
Trial 3: 2.453125 seconds
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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 the average speed of the object as it moved, I first found the average of all of the time intervals. By doing this I determined the average time for the distance traveled by the can was 2.493490 seconds.
In order to find the average speed, I took the distance traveled (230 mm) and divided it by the average time (2.493490 seconds) to get 92.24 mm per second. I believe that this is a somewhat accurate measurement of the object's average speed. The limiting factor to how accurate the average speed can be calculated in the limited amount of data collected.
With only six total time intervals collected, the average speed is based on little data. If we were to take 20 more time intervals for each direction and use that data, I would have more confidence that my average speed was more accurate.
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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:
To object was moving very slow at the beginning of the timed interval but picked up speed as it went along the book.
The average speed for the time interval was 92.24 mm/sec.
I believe that when the object reached the lower end of the book, it was moving at a speed greater than the average speed I calculated.
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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:
Least to Greatest
1. Object's Initial Speed
2. Ties: Average Speed and Change In Objects Speed As It Rolled From One End Of The Book To The Other
3. Object's Final 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:
I set the book and prop up in the exact same manner as for my initial timing experiment. Since the distance traveled and measured for the object in the initial experiment was 230 mm, I found half that distance (115 mm) and marked it on the book.
This time when I released the can I clicked the timer. I then clicked the timer when it crossed the halfway point (115 mm) and when it crossed the end point (230 mm). By measuring the time over the first half and second half of the distance traveled, I could see that the object was speeding up.
My data is as follows:
Time Trial Time Interval From Initial Point To Halfway Point Time Interval From Halfway Point To End Point
1 1.750000 seconds .7695313 seconds
2 1.878906 seconds .7500000 seconds
3 1.828125 seconds .7226563 seconds
It is obvious from the data that the can is speeding up as it goes along. It takes the majority of the time for the can to travel the first half of the distance on the book as oppose to the second 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?
1.5 hours
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You may also include optional comments and/or questions.
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&#Very good data and responses. Let me know if you have questions. &#