phy201
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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6/13 12
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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 a book called Gorgeously Green Diet. It is about 19 cm by 24 cm and I used the car included in the lab kit. I originally tried using only 3 quarters to prop the book up
but the car wasn't rolling consistently at that incline so i added 3 pennies to the pile to make the incline steeper. The car rolled a little inconsistently. Sometimes it took longer to
start up and other times it rolled at a slight diagonal.
#$&* (note that your answer should always start in one of the blank lines preceding the #$&* mark)
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:
Initial roll measured 5 times 180 degree/ roll measured 5 times
1.53125 s. 1.765625 s.
1.65625s. 1.75 s
1.75 s. 1.84375 s.
1.4375 s. 2.078125 s.
1.828125s. 1.703125 s.
the car traveled about 19 cm across the book each time.
the difference in height from one end of the book to the other was 1 cm
the supports were located 20 cm from the other side of the book
these measurements were consistent when the book was rotated 180 degrees as well as with the original.
I'm not sure the roll each time was entirely consistent.The car seemed to start off slower at times ( the wheels would get stuck) and there
was also error on my part in terms of the directionality of the car. I f my hand was tilted slightly the car might roll at a diagonal making
the distance traveled a slightly higher number.
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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 five rolls the average time was 1.641 sec. making the average speed 11.58 cm/sec. When rotated 180 degrees the average
time was 1.828 making the average speed 10.39 cm/sec. The average speed of all rolls combined would be about 10.9 cm/sec. These averages are
probably accurate to the first decimal place. Some of the rolls were calculated to the fifth or sixth decimal place and others were only
calculated to the second. When I averaged these numbers I left all the decimal places given to me by the timer program and only rounded once
I divided by the 5 rolls. There would also definitely be some error with the smoothness of the runs, as mentioned above,
so it's hard to be truly 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:
I'm not sure exactly how to claculate this. ??? Do you mean how fast was it moving at the beginning of one of the rolls that I timed????
How whould you get an exact clacualtion of this?? I do know that it was moving slower than the average speed since the car started from a
rest position and got faster as it moved down the incline.Once the car reached the lower end it was traveling at a greater speed than the a
average.
You have answered the stated question. The ball was moving at 0 cm/s at the beginning of the interval, and faster than the average velocity at the end of this interval.
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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
change in speed
average speed
final speed
the initial speed of the car would be the least because it is starting from a rest position. As it picks up momentum going down the hill the speed becomes faster and faster
so the final speed would be the greatest. i think the change is speed from one end to the other would be greater than the average speed because
you are subtracting the initial from the final speed versus taking an average of the changing speeds.
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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 taped a sheet of paper with measurements at 5 cm, 10cm and 15 cm starting past the point of the start position of the car. Then I put a
barrier at the 5cm mark so the car would stop at this point and timed it 3 different times from the start position to the barrier. I then did the same thing
for the 10 cm and 15 cm markings. My data is as follows:
5cm 10cm 15cm
.65625 s. .890625 s. 1.140625 s.
.625 s. .82125 s. 1 s.
.609375 s. .921875 s. 1.078125s.
average: .629 s. .880 s. 1.073 s.
speed: 7.95cm/s. 11.36 cm/s. 13.98 cm/s.
This data proves that the car does speed up as it moves down the incline.
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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?
an hour and a half
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You may also include optional comments and/or questions.
&#Good responses. Let me know if you have questions. &#