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

You may enter any message or comment you wish in the box below:

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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, Physics by Giancoli, 6th ed., for my ramp, and I used an empty cardboard container without a lid for my object. The container was 13.4cm in length and 6.4cm in diameter. I used 55 sheets of paper (GP Image Plus, Multipurpose, Bright White 145, 92 Brightness, Standard Wt. 20lbs) as a prop for the book. The container rolled well. It rolled smoothly, didn't speed up and slow down, rolled in a straight line, and didn't change directions.

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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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Using the timer program, I measured the time it took for the container to roll from one end of the ramp (book) to the other, when released from rest. I completed three trials with the setup in the initial orientation (1-3 below) and then reversed the direction of the book on the tabletop, rotating the book and the prop 180 degrees so that the container rolled in exactly the opposite direction (4-6 below). I completed three trials with the setup in the second orientation. I believe the measurements are accurate to +/- 0.3sec. The results are listed below in seconds.

1 1.6875

2 1.78125

3 1.78125

4 2.59375

5 2.84375

6 2.328125

Additional notes: The distance the container rolled during all trials was 21.9cm. The lower end of the book was measured to be 3.7cm high and the end with the prop was measured to be 4.3cm high, a difference of 0.6cm. The length of the book was 28.3cm.

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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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Ave. Vel. = 21.9cm/(Ave. time for all 6 trials (in sec.))

10.1cm/s. Because of the error introduced when using the timer, I believe the velocity can be estimated to be accurate to +/- 0.1cm/s.

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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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To determine whether or not the object is speeding up as it rolls down the incline, repeat the experiment using another distance. Do not change the prop height. Then take the data and compare it to the data from the initial experiment. I used 21cm for a distance rolled of 14.6cm. See the data below.

1 1.5000

2 1.46875

3 1.484375

4 2.03125

5 2.25

6 2.171875

Average velocity = 8.03cm/s.

At 14.6cm, the container was moving at 8.03cm/s, but from the initial experiment we see that the container was moving at 10.1cm/s when it reached the distance of 21.9cm. So we can see that the speed of the container increased between those two distances.

Your statement isn't quite correct, though your results do support the hypothesis that the object speeds up. The container averaged about 8 cm/s for the first 14.6 cm; since it started from rest it's most likely moving faster than that when it reaches the 14.6 cm point. It averaged about 10 cm/s for the entire 21.9 cm.

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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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2 hours

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

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Good work. See my notes and let me know if you have questions. &#