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Phy 241
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 **
945pm 9/4/2012
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Initial Timing Experiment
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Follow the instructions, fill in your data and the results of your analysis in the given format.
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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 used the University Physics w/ Modern Physics Edition 12 by Young and Freeman. ISBN 978-0-321-50121-9. The book's cover is straight and unbent. It measures 8 5/8 inches long and
22.2 cm wide. It's a fairly thick and heavy book. I used one domino from the lab kit to prop up the book. I used this domino because it sits just as high as a stack of quarters.
I used a little red Hot wheels car that came new out of the box with the lab materials. The car rolls smoothly. It begins to speed up as the car is slightly tapped into motion across the length of the book
It rolled in 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:
The distance the toy car travels was measured by the full-size ruler print-out offered as a downloadable document in this course. The back wheel of the
car is placed on the edge of the book so as no to roll. The distance from the tip of the hood of the car to the end of the book was measured as 23.11 cm.
The domino is 9.1 cm thick and this is how much higher the book now sits on one end, vs the end thats flat against my desk. The book measures 8 5/8 inches long and
22.2 cm wide. I believe the accuracy of the measurements is fairly certain. The measurements for the timer.exe is also accurate, but both the measurements
of the timer and the lengths and widths of everything else do have some minor human error. Depending on how hard I nudged the car from its stop affected the speed of the car, so I would try to barely
nudge it with the slightest tap to get it going.
A trend that occured was when I first tapped the car into motion and when the car reached the length of the book, I had to click on the timer. This small amount of time(fraction of a second)
is what I consider human error. To try to eliminate that, I put my labtop and experiment in the same periphireal.
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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:
trial 1
v_0 = 0
'dt = 1.227 s
'ds = 23.11 cm
v_f = 18.83 cm/s
trial 2
v_0 = 0
'dt = 1.219s
'ds = 23.11 cm
vf_ = 18.96 cm/s
trial 3
v_0 = 0
'dt = 1.289s
'ds = 23.11 cm
v_f = 17.93 cm/s
Average of the 3 trials:
('dt_1 + 'dt_2 + 'dt_3) / 3 = 1.245 s
23.11 / Ans = 18.56 cm/s
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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/s at the beginning of the timed interval.
Average speed during this interval is 18.56 cm/s
The object was moving at a speed greater than the average speed I calculated, because the average speed is the final + the intial divided by two.
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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
intial speed
average speed
final speed(tie)
change in speed(tie)
greatest
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*#&!
&#Your work on this lab exercise is good. Let me know if you have questions. &#