initial timing experiment

Phy 231

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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For the experiment, I used a can of Campbell's Beef Broth (full, unopened) with a mass of 298g. The can is approx. 10.5 cm tall, with a diameter of about 7cm. For the flat surface, I used our Physics book (ISBN: 987-0-321-50121-9).

I used a stack of paper to prop the object up. In measuring the height of the book with the paper under one end, it was 5.9 cm. The other end of the book was 5.6 cm, meaning I used approx. 0.3 cm of paper to make the book into an inclined surface.

The can rolled pretty smoothly - I somewhat expected this, but thought it might roll awkwardly depending on if the contents of the can shifted to one side during the roll or not. I suppose that since the can is full, there isn't much room for the liquid to move around, so this wasn't a factor. The roll was essentially straight, unless I aimed it incorrectly. It appeared to start slowly and then pick up speed as it moved down the incline.

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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 amount of time in seconds for the can to move from a resting postion at the top of the incline, to the point at which the can fell off of the bottom of the book (the bottom of the incline). With one hand, I held the can in a resting position, and with the other hand, I clicked the mouse. I tried to synch up the timing for clicking the mouse and lefting go of the can at exactly the same time; this took a couple practice tries. I believe I was reasonably accurate, though obviously I could have clicked the timer early or late by a fraction of a second. Overall though, I believe I did OK in accurately gauging the time from top to bottom of the incline.

1st Run, can moving left-to-right

# Roll Time (in seconds, rounded to hundreths of second)

1 2.53

2 2.38

3 2.73

2nd Run, can moving right-to-left

# Roll Time (in seconds, rounded to hundreths of second)

1 2.98

2 2.74

3 2.79

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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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By taking all 6 measurements, I sum them to get a total of 16.15 s. I then divide that # by the total # of attempts (6) to get 16.15 s/ 6 = 2.69 s.

Measuring the length of the book, it totals approx. 30.2 cm. I can then divide 30.2 cm by 2.69 s, to get:

30.2 cm / 2.69 s = 11.23 cm/s

Because of errors in correctly gauging the time from start to finish of the can rolling down the incline, there may be slight error in the average velocity as calculated. However, I believe I have made a reasonable calculation of what the average velocity was for this experiment.

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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 if the can is actually speeding up as it moves down the incline, I have determined what the middle point of the incline is; I will then record the time of the can as it moves past this intermediate point and then again as it hits the end of the book.

Just from taking the measurements, I can tell the can is speeding up, because of the amount of time it takes to reach the midpoint versus the amount of time it takes to travel from the midpoint to the endpoint.

The measurements and average speeds are as follows:

# Roll Time - Midpoint (in seconds) Time - Endpoint (in seconds)

1 1.56 0.94

2 1.34 0.93

3 1.49 0.96

Average time to reach midpoint = 1.46s. Average time from midpoint to endpoint = 0.94s.

The distance from beginning to midpoint = 15.1 cm, so the average speed = 15.1 cm / 1.46 s = 10.3 cm/s.

The distance from the midpoint to the endpoint = 15.1 cm, so the average speed here is = 15.1 cm / 0.94 s = 16.1 cm/s

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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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This experiment took approx. 75 mins.

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

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&#Your work on this experiment looks good.

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