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 Giancoli Physics book placed on a wood table with a wood shim of height 4 mm placed under one end. The book measures 284 mm from end to end on the long side, this is the length of the ramp. The book is in used condition, and has minor imperfections, but there is no indication that the surface has any irregularities that would hinder the motion of the can. The ISBN is 0-13-060620-0. The rolling object was a full and unopened metal can of Libby's 100% Pure Pumpkin the can measures 113 mm in height with a diameter of 75 mm. The net weight of the contents is 425 g. The experiment was performed at room temperature, approximately 70 degrees Fahrenheit. The can rolled in a straight line from one absolute edge of the book to the other. The measurement was taken as soon as the can began to fall off the book. The can accelerated as it rolled. The acceleration seemed fairly constant throughout. The rolling of the can was smooth throughout as well, the can has no noticeable dents or imperfections.

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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 can was held at the point where it was perfectly balanced on the edge of the book and then rocked forward approximately 1mm, at which point it was realeased. The timer program supplied with the class was started at the moment of release. The timer was stopped when the can reached the edge of the book and began to fall towards the table. I believe the measurements are accurate within 3 tenths of a second.

Run 1 - Rolling from East to West

Distance covered: 284 mm while descending 4mm

Times in seconds

1) 2.899

2) 3.023

3) 2.648

4) 2.929

Average time in seconds: 2.875

Run 2 - Rolling from West to East

Distance covered: 284 mm while descending 4mm

Times in seconds

1) 3.007

2) 3.484

3) 3.070

4) 2.976

Average time in seconds: 3.134

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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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For run 1 the average speed was 284 mm / 2.875 = 98.78 mm/sec

For run 2 the average speed was 284 mm / 3.134 sec = 90.62 mm/sec

The average of all trials was 94.7 mm / sec

I believe that these measurements are accurate to with +/- 10 mm / sec. This is approximately 10% of the total value, ans I believe that the original time measurements were accurate to within about +/- .3 seconds or roughly 10% of the original times.

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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 repeated a set of measurements where I set up the experiment exactly as before except that the can was started in the exact middle of the ramp. The times were as follows:

Distance traveled: 142 mm down a slope of 2 mm descent

Times:

1) 1.906

2) 1.953

3) 1.906

4) 1.820

5) 2.078

Average time: 1.932 sec

Average speed = 142 mm / 1.932 sec = 73.5 mm / sec

Therefore, we can conclude that the can does indeed accelerate as it goes down the ramp. It only reaches an average of 73.5 mm/sec on the half ramp vs. 94.7 mm/sec for the full ramp.

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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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About one hour and 15 minutes.

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

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Excellent report.