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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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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:
For this experiment I used a brown clipboard as my ramp and I used the little match box car from the lab kit. To prop the ramp up I used one domino from the lab kit and a piece of paper folded four times. The match box car rolled fairly well, it increased it's speed as it left from the initial point on the clipboard and rolled in a straight line and did not change direction.
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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:
I measured the clipboard, the incline of the ramp with the cm ruler from the lab kit, and the amont of time it took for the object to roll down the incline. I believe I measured these items very acurately 9.
Clipboard length= 27cm
Ramp= 1.5cm
Elapsed time= 2.2sec
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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:
Using the formula r=d/t I detemined that the average speed of the object rolling down the incline was 12.3 cm/sec.
Accuracy was 8-9 and I believe I was this acurrate because I accurately measured the distance that the object rolled as well as the time that it took for the object to reach the end of the clipboard.
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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 object was moving at 0 cm/sec at the beginning of the the timed interval. The average speed during the time interval was 12.3 cm/sec and the objects speed was greater at the end of the ramp then at the beginning.
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@& If the initial velocity was zero and the final velocity was 12.3 cm/s, then the average velocity would be somewhere between 0 cm/s and 12.3 cm/s. The average velocity would not be 12.3 cm/s.
However as you found, the average velocity is 12.3 cm/s.
If the initial velocity is zero and the average velocity is 12.3 cm/s, then the final velocity would need to be greater than 12.3 cm/s.
What therefore do you think the final velocity was?*@
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 = 0
Final speed = 0
Change in speed = 5.6 cm/sec
Average speed = 12.3 cm/sec
The objects initial speed was zero because the object was not in motion , it's final velocity was zero because the object stopped moving. The change in speed was determined because the formula for change in speed or “acceleration” is a = v2 - v1 / t2 - t1 so a = 12.3 - 0 / 2.2 - 0 = 5.6 cm/sec.
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There is no assumption that the object stopped moving during the interval being considered. In fact you have already stated a final speed that wasn't zero.
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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 put the ramp at different angles, at a lower angle using only one domino with out the folded paper the car moved more gradually, and at higher angles the car moved more suddenly. With all the angle test the car had a change in speed but was slower or faster depending on the angle of the ramp.
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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 me about an hour and a half to complete this experiment.
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You may also include optional comments and/or questions.
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@& You're doing a good job of describing your thinking.
See also my notes and give this a little more thought. Don't spend more than 20 minutes on revisions, then resubmit as indicated below.*@
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&#Please see my notes and, unless my notes indicate that revision is optional, submit a copy of this document with revisions 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.
If my notes indicate that revision is optional, use your own judgement as to whether a revision will benefit you. &#