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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.
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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 is Essentials of Musculoskeletal Care 3rd ed. ISBN 0-89203-352-5. It is 28.0cm x 22.4cm x 4.4cm. I raised one end of
the boo using one of the dominos in the initial lab materials, it is 0.8cm in thickness. I used a rubber ball with a circumference
of 14.6cm, a radius of 2.3cm, and a mass of 46g. The ball rolled smoothly and its speed increased as it rooled down the incline.
It generally went in a straight line, but did angle to one side some times. I discarded these results.
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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 how long it took the ball to roll down 26.5cm of incline when one edge was raised by 0.8cm. In the first direction I
recorded an average time of 2.1668s and an average of 1.2598s in the other direction. I used 4 different times in each direction
when the ball rolled relatively straight.
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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 the first direction, the ball rolled at a rate of 12.2cm/s on average and a rate of 21.0cm/s on average in the second
direction. I beliefe this measurement is only accurate to 0.1cm/s. This is because the ruler I used was in mm and therefore could
not be more accurate than 0.1cm. This limits the results overall to an accuracy of 1 significant figure after the decimal.
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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 very instant the timing started the ball was moving at 0.0cm/s. On the average, the speed was either 12.2cm/s or 21.0cm/s
depending on the direction. I believe the ball was rolling faster than the average at the end. If not, that never would have ben
the average, since the ball was only increasing in spped the further it rolled.
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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 a tie between the change in speed and the 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 used the same setup in the first direction and calculated the average speed of the ball rolling almost halfway down the book. I got an average time of 1.2852s to roll 13.2cm which gives an average speed of 10.3cm/s. This is 1.9cm/s slower than the average speed for the ball rolling the length of the book. If the ball was not speeding up the further it rolled, the avg speed for the whole book would be equal to or less than the avg speed to roll down half the book.
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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?
About 45 minutes.
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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. &#