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Phy 201
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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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 used our Physics book ISBN 0-13-060620-0 approximately 282mm (length) X 223mm (width) X 37mm (thick) with 5 CD’s to prop it up. 1 of the CDs had a yellow jewel cover under the side and the book set on them approximately ½ way. I used a “power liner” dry erase marker as the rolling object. The 1st set of timing averaged between 1.2 to 1.6 seconds, but when I reversed the book and the CDs, the marker seemed to slow down to about 1.35 to 1.64 seconds. The marker rolled pretty smoothly but did swerve a little due to its irregular shape. The times were a bit fast but were better for consistency.
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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:
When I measured the length of the path traveled by the marker, I subtracted the radius times two because I timed the event from the starting point of the top edge of the book lined up with the edge of the marker looking directly on top of it. The end point of the event was when the marker hit my hand which was straight up and down with the book. The distance the marker traveled was 263mm
In the timer program I rounded all the numbers to 2 decimal places. Times for marker going from right to left were: 1.42 sec, 1.26 sec, 1.20 sec, and 1.60 sec.
Times for left to right were: 1.46 sec, 1.35 sec, 1.75 sec, and 1.64 sec.
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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:
(right to left) Add times and divide by 4 to get avg time:
1.42+1.26+1.20+1.60=( 5.47)/4=1.37sec
Ave Rate=Ave dist/Ave time Ave Rate=263mm/1.37sec=192mm/sec
(left to right) Add times and divide by 4 to get avg time:
1.46+1.35+1.75+1.64=(6.2)/4=1.55sec
Ave Rate=Ave dist/Ave time Ave Rate=263mm/1.55sec=170mm/sec
The accuracy of the events are most likely within about 10 mm not counting for human error. The human error factor counts on human reaction time to accurately time and measure the distance of the experiment. If we used machines, or computers to time the experiment, then the results would be more consistent. The main contribution to error is in the timing portion.
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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:
The object started from rest, and when released, accelerated at an exponential rate up to at least 100mm/sec.
From right to left it was 192mm/sec and from left to right it was 170mm/sec.
I was moving at a greater speed than the average speed because we know that the marker started at rest and it had to accelerate, so that must mean that the ending speed was greater than the initial speed. Also we know that the acceleration of the marker was due to the effects of gravity.
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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 was the least, followed by average speed and final speed was the greatest. The initial speed was least, and the time it took to travel a set distance was greatest at this point. The average speed is a value that determines the median of the initial and final speed. The final speed will be greater than the average speed and is pretty much the opposing spectrum of the initial speed.
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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:
I used the set up as before with our Physics book and the CDs. However in order to prove that the object was speeding up, I decided to compare the average speed from 2 distances. The first distance was at 125mm. (On the back of the book, the distance from the bottom of the book to the bottom of the picture of the mountain is 125mm.) The times I got were: 1.33sec, 1.19, 1.70 and 1.14. The avg. time is 1.34sec. The avg dist will stay the same at 125mm the avg speed is (125mm/1.34sec = 93.28mm/sec).
Then I measured the avg speed the same way from end to end of the book which is 282mm. I did not subtract the radius of the marker for both runs because the effect was negligible. The times of the end to end roll were: 2.09sec, 2.11sec, 1.94sec and 1.88sec. The avg time is 2.01 The avg dist will stay the same at 282mm the avg speed is (282mm/2.01sec = 140.3mm/sec).
As we can see, the avg speed of the longer distance is greater than the shorter one proving that the marker was accelerating.
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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?
2 hours
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You may also include optional comments and/or questions.
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&#Very good responses. Let me know if you have questions. &#