initial timing experiment

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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Initial Timing Experiment

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In this experiment you will use the TIMER program, a hardcover book, 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 on the Assignments page).

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.

Then reverse the direction of the book on the tabletop, rotating the book and its prop 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 solid glass marble, a small can of tomato paste (full or empty?), a ball-point pen), 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?

Note:  Don't trust this form.  Compose your answer in Notepad or a word processor, saving it every few minutes, then copy and paste it into the box.  Power could surge, your computer could malfunction, in any of a number of ways the work you put into this form could be lost.  Compose it elsewhere and keep a copy.

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I used the Physics textbook (ISBN 0-13-060620-0). To prop up the textbook, I used a small, thin metal generic tin that was 2cm thick. For the rolling object, I used a can of Campbell's chicken noodle soup, weight was 10.75 fl oz.. The book's length was 28.5cm. The object moved very smoothly and in a straight line on all attempts. The object appeared to speed up.

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In the box 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 see any patterns that might occur.

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The book was measured at 28.5cm with a ruler. I measured the height of the tin that was used to prop the book, it was 2cm thick. The can was used as the object and it weighed 10.75 oz. I believe the measurements to be very accurate.

1st roll - timed interval was .90625

2nd roll - timed interval was .71875

3rd roll - timed interval was .75

Averaged time: .79167

After the book was rotated 180 degrees, these are the readings I got.

1st roll - timed interval was ..890625

2nd roll - timed interval was .859375

3rd roll - timed interval was .78125

Averaged time: .84375

It appears as though the 1st set was faster than the 2nd set.

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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.

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I determined that the can was moving at a rate of .027778sec/cm. I arrived at this estimate by dividing the average of the 1st trial set by the centimeters of the book, 28.5cm. I believe that the speed is not very accurate due to the fluctuation of the timed trials and the human error ratio for the timer program.

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Devise and concuct 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.

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I used the setup from the previous experiment and marked off the half way point of the book, 14.25cm. I took three time trials, these are the results:

1st roll – timed interval was .46875

2nd roll – timed interval was .5625

3rd roll – timed interval was .625

Average time: .55208

I then took the average from the 2nd time trials from the 1st part of the experiment (.84375) and subtracted from it the average of this time trial. The difference ended up being .29167. This is the amount of time it took to complete the last 14.25cm of the roll. So it proves that it does indeed speed 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: 

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45 min.

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You may add optional comments and/or questions in the box below.

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&#Very good responses. Let me know if you have questions. &#