initial timing experiment

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 book entitled Physics, sixth edition, by Giancoli. The length of the book, and thus the distance the object travels from one end to the other, is approximately 28.3 cm. The side of the book that is propped up is 1.4 cm higher than the end that is resting on the desk. I set up the experiment on the surface of my computer desk. I used a plastic CD case to prop up the book. The object I used to roll is an aluminum can full of cream of mushroom soup. The object rolled smoothly, it seemed to speed up at the lower end of the book, and it rolled in a straight line.

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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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I measured the time if took the can to travel from one end of the book to the other end using the TIMER program. The first set of measurements of the time it took the can to roll along the length of the book include the follwing times: 2.3125 seconds, 2.375 seconds, and 2.3844 seconds.

After rotating the book 180 degrees and following the same procedure, I obtained the following rolling times: 2.28125 seconds, 2.8218 seconds, and 2.46875 seconds. I believe the measurements are fairly accurate, but could be slightly flawed because I was trying to click the TIMER program and release the object simultaneously and there could be some error because of that.

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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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The average of the first set of times is 2.357 seconds. You can determine how fast, on average, that the object is moving by dividing the distance traveled by the average time it took to travel that distance. Using this formula, we find that 28.3 cm/2.357 seconds=12.0 cm/seconds. Using the same method, we find that after rotating the setup the object moved down the incline 28.3 cm/2.7062 seconds=10.5 cm/second on average. Assuming the timer program is accurate, I believe the object's speed was determined very accurately because I measured the distance traveled accurately, and then calculated the average time it took to object to roll, so the speed should be accurate.

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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 added another CD case to prop up the book, so the higher side of the book is now 2.1 cm higher than the lower side. If the can is speeding up as it goes down the incline, then the higher incline should produce faster times than the lower incline. The data for the steeper incline include the following times: 1.328125, 1.296875, and 1.3125. When finding the average speed, we get 28.3 cm/ 1.3125 seconds=21.6 cm/second, on average. Comparing that with the initial average speed of 12.0 cm/second, we see that with the steeper incline the can does in fact roll at a higher speed.

This shows that the can has a higher average velocity on the steeper incline.

Note that when we refer to 'initial', 'average' and 'final' velocities, we are referring to velocities that occur during some time interval. 12.0 cm/s is an average velocity achieved by the object accelerating from rest on a certain incline where the initial velocity during the timed interval was 0 and the displacement was about 28 cm. When you changed the incline you timed another similar interval, on which you observed a shorter time; that interval had its own initial, average and final velocity.

In any case, very good work on this introductory experiment.