initial timing experiment

Phy 201

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 set my experiment in a fairly simple manner. I used my Physics by Giancoli book, ISBN number 900130606203. It measured 28 cm in length. I used a brand new spool of thread as the object I was rolling down the book. I used one domino that was 1 cm high to prop up the book to create the incline. The spool of thread rolled pretty smoothly down the book during my trails. It stayed straight every time and it appeared to increase in speed as it descended down the book cover.

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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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In Trial 1, I set everything up just as I was instructed to do. The book (28 cm) was propped up 1 cm by a single domino. The roll of thread was set at the higher end of the book, then released. The time was taken to see how long it would take the thread to roll from one end of the book to the other. I repeated the experiment 3 times. In Trial 2, all I did was turn the book 180-degrees and repeat the experiment.

Trial 1

Time: 1.962 seconds

2.060 seconds

1.989 seconds

Trial 2

Time: 2.603 seconds

2.016 seconds

2.520 seconds

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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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During Trial 1, the average speed of the roll of thread was 13.97cm/second. I determined this speed by first finding the average time the thread rolled down the book by adding (1.962+2.060+1.989)/3 = 2.004. Then I simply divided the 28cm book by the average 2.004 seconds it took the thread to roll, and came up with 13.97cm per second. I did the same in Trial 2 and came up with an average speed of 11.76cm/second. I can say with a fair amount of certainty that these measurements are pretty accurate. Unless of course my ruler is a little off or I did a poor job of starting a stopping the clock, these measurements are as close as I could get them.

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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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What I did was I basically split the book in half at the 14 cm mark. Everything was set up the same as during the initial experiments, except that I had the ruler sitting at the 14cm mark. I rolled the thread down the book as usual, but it would crash into the ruler just before it was gaining speed. The average time of 3 trails the thread took to hit the ruler was 1.284 seconds. I then did the same experiment but this time I removed the ruler and didn't start the clock until after the thread rolled past the 14cm line. To the best of my ability I ran 3 trials and got an average time of 0.905 seconds. Thus, this data supports my previous assumption that the thread is in fact speeding up as it rolls down 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: 

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It took me about 45 minutes to complete.

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

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&#Good responses. Let me know if you have questions. &#