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Phy 121
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.
** Initial Timing Experiment_labelMessages **
6/11/12 at 3:30 PM
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Note: The majority of student report taking less than an hour on this experiment, though a few report significantly longer times.
Take reasonable care to get good data in this experiment. Try to do the timing as accurately as possible. Measurements of length, height, etc. should be reasonably accurate (e.g., with a meter stick or ruler you can measure to withing +- 1 millimeter, but it's not necessary to try to determine fractions of a millimeter).
In this experiment you will use the TIMER program, a hardcover book, the toy car that came in your lab materials package (or, if you do not yet have the package, 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, which is also given on the Assignments page).
• The book's cover should be straight and unbent.
• The toy car (or other object) should roll fairly smoothly.
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. For a typical book, a stack of two or three quarters placed under one end works well.
• Using the TIMER program determine how long it takes the ball to roll from one end of the ramp to the other, when released from rest. Once you've got the book set up, it takes only a few seconds to do a timing, so it won't take you long to time the object's motion at least three times.
• Determine how far the object travels as it rolls from its initial position (where you first click the timer) to its final position (where you click at the end of the interval). This will probably be a bit less than the length of the book, due to the length of the object itself.
• Determine how much higher one end of the book was than the other, and how far it is from the supports (e.g., the stack of quarters, or whatever you used to support one end) to the end of the book which rests on the table.
Then reverse the direction of the book on the tabletop, rotating the book an its supports (e.g., the stack of quarters) 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 can of vegetables (full or empty; should be specified) or a jar (again full or empty); anything round and smooth that will upon release roll fairly slowly down the incline), 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?
your brief discussion/description/explanation:
I am working with Susie Coleman in the Math Emporium at Virginia Tech. We are at a level table. We used the 11 inches long, “Physics” by Giancoli sixth edition textbook in order to make our ramp. The object used was a 5 oz cylindrical tube of Palmer’s Cocoa Butter Formula chapstick with a diameter of 2 cm. To prop up the textbook we used Styrofoam that is 0.5 inches thick. The speed increased slightly and it rolled in a straight line.
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In the space indicated 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 identify any patterns or trends.
your brief discussion/description/explanation:
Textbook: 11 inches long and 1.5 inches thick
Supporter: 0.5 inches thick
Supporter to the end of the text on the table: 10.5 inches
Lowest point of ramp: 1.5 inches
Highest point of ramp: 2.0 inches
Diameter of cylinder: 2.0 cm
The chapstick rolled 10.5 inches from the start of the timer to the end of the timer. The average time that it traveled during the first trial from right to left was 1.09 seconds. In the second trial from left to right it traveled at an average time of 1.06 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.
your brief discussion/description/explanation:
Trial 1 (Right to Left): Avg. 1.09 seconds/10.5 inches
Overall average speed is 0.104 seconds/1 inch
Trial 2 (Left to Right): Avg. 1.06 seconds/ 10.5 inches
Overall average speed is 0.101 seconds/ 1 inch
I feel as if I determined the objects average speed pretty accurately. Each trial was timed three times in order to give us the average speeds. All three times were highly close to one another for both trials. Furthermore, there is experimental uncertainty when taking human error into account. While using the Timer program it is possible that I did not click the timer at the exact start or end point. However, I believe that the average speed would still be within .02 seconds even if I had delayed with the program.
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How fast was the object moving at the beginning of the timed interval?
According to your previous calculation, what was its average speed during this interval?
Do you think the object, when it reached the lower end of the book, was moving at a speed greater or less than the average speed you calculated?
your brief discussion/description/explanation:
At the beginning of the timed interval the object was moving only slightly slower than it was at the end of the timed interval. We consider the first two inches travelled qualifies as the beginning of the timed interval. Since the overall average speed for Trial 1 (right to left) is 0.104 seconds/ 1 inch we find the average speed at the beginning as follows:(0.104 sec/1 in)/ 2 in = 0.052 sec/ in. Since the overall average speed for Trial 2 (left to right) is 0.101 seconds/ 1 inch we find the average speed at the beginning as follows:(0.101 sec/1 in)/ 2 in = 0.055 sec/ in.
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For point of reference we measure the speed of our automobile in miles / hour or kilometers / hour, not in hours / mile or hours/ kilometer.
So you would divide the distance by the time required, obtaining speed in this case in units of inches / second.
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List the following in order, from least to greatest. Indicate 'ties': The object's initial speed, its final speed, its average speed, and the change in its speed as it rolled from one end of the book to the other.
your brief discussion/description/explanation:
Initial speed < average speed < final speed. As it rolled from one end of the book to the other in both trials the speed slightly increased. This is most likely due to the increase of momentum as the chapstick rolled down the incline.
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Devise and conduct 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.
your brief discussion/description/explanation:
We chose to use the same set up as previously indicated. With pencil, marks were made along the edge of the textbook to indicate one inch, with a total of 11 marks (since the textbook is 11 inches long). Since we previously stated that the first 2 inches traveled qualifies as the beginning, the interval between 4 and 6 inches would be the middle and the interval between 8 and 10 inches would be considered the end. First, we timed how long it took the chapstick to travel from 0 inches to 2 inches three times using the Timer program. Next, we timed how long it took the chapstick to travel between 4 inches to 6 inches three times by starting the timer once the chapstick reached the 4 inch mark and stopping it at the 6 inch mark. Finally, we timed how long it took the chapstick to travel between 8 inches and 10 inches three times with the corresponding method. The table below includes the corresponding times and averages.
From 0-2in From 4-6in From 8-10in
Time 1 (sec) .420 .250 .195
Time 2 (sec) .452 .277 .204
Time 3 (sec) .469 .230 .211
Average Time (sec) .447 .252 .203
As you can see, it is obvious that the amount of seconds decreases the most between the “beginning” and “middle” but still decreases from the “middle” until the “end”. This does signify that the object’s speed increased as it travelled down the 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:
Approximately how long did it take you to complete this experiment?
This took me approximately 2 hours.
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You may also include optional comments and/or questions.
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&#Good work on this lab exercise. See my notes and let me know if you have questions.
Revision isn't requested, but if you do choose to submit revisions, clarifications or questions, please insert them into a copy of this document, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
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