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phy121
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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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 used is Elctrical Circuits Fundamentals by Floyd. ISBN: 978-0-13-507293-6. I used a marble and used dominos to prop the book up. the book was elevated about 8mm and distance from the base to the support was 26 cm (260mm) The marble rolled very smoothy, in a straight(although slanted) line. The marble speed increased as it traveled down the incline.
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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 distance of the incline from top to bottow is 28.5cm I measured this by measuring the length of the book, and the size of the marble and the difference was 28.5 cm +/- .5cm. I released the marble from rest at the very top of the incline. I clicked the timer as soon as I released the marble. I stopped the timer as soon as the marble appeared to be at the edge of the book. The time measurement is probably accurate within .15 seconds.
Run 1: 1.871 seconds
Run 2: 1.722
Run 3: 1.707
Run 4: 1.726
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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:
the average time was 1.7565 seconds. 28.5 cm / 1.7565 seconds = 16.225 cm/second. I believe this to be accurate within 2.22 cm/sec. I got this from the following: I estimate the distance to be accurate within .5 cm, and the time to be acurate within .15 seconds. That means the distance could be as high as 29cm or as low as 28cm. The time could be as short as 1.6065 seconds and as high as 1.9065. The fastest rate from these estimates would give 28cm /1.6065 and the slowest 29/1.9065. This gives 17.429 and 15.211 respectively, with a difference of 2.22 between them.
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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 beginning the object was at rest, so its verlocity was zero. The average would be the same as calculated before, since it started at rest: 16.225 cm/sec
It would have been moving at a greater speed than the average, because it was accelerating at a constant rate.
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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 change in speed from one end to the other is a tie, and then 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:
Time the object takes to travel from the start of the incline at rest, to the half way point (14.25 cm) I marked the book with a piece of tape to indicate the half-way point. I timed the marble from start to halfway, then measured from teh halfway to the end.
It took the marble 1.05 seconds to travel the first half, and .6 seconds to travel the second half. It is clear the marble is speeding up.
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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?
Less than 1 hour
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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. &#