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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.
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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:
To create the incline, I used two paperback books stacked on top of each other, measured at a height of approximately 1.5 cm. The rolling surface, a scrabble game board, was 37 cm, the object rolled, a toy car, was 7.5 cm, resulting in a distance travelled of 29.5 cm. Rolling from left to right the toy car took an average of 1.6 (1.7, 1.6(4) 1.7,) seconds to travel the measured distance. When the incline was reversed 180 degrees and rolled right to left, similar measurements followed. The object took an average of 1.5 (1.6, 1.6, 1.5, 1.4, 1.5, 1.5) seconds to travel the measured distance. In some trials the car would not move at a high enough velocity to complete the scrabble board and would stop with one set of wheels off and one on. I tried to compensate for this which may have accounted for the slight difference in measurement, but I do not believe it effected the overall accuracy of the experiment.
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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:
For the items involved in this experiment, I measured them all with a measuring tape that home depot gave me that is scored with inches and centimeters. The measurements for the objects are listed in the previous question. I am sure the measurments on the tape were accurate but in some instances the car behaved differently on opposing sides (when the slope was reversed 180 degrees) and it was difficult to get a consistent timing measurement. After some adjustments they matched up more, but these adjustments would not have hindered the reliability of the accuracy in question.
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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:
The object moved at a speed of 18.4 centimeters per second, or one centimeter every 0.05 seconds if we use the data of the car rolling left to right (29.5 cm in 1.6 seconds). If we use the reverse right to left (29.5 cm in 1.7 seconds) we get 17.4 centimeters per second or one centimeter every 0.06 seconds. I believe the measurements to be as accurate as possible, I used the timer and took multiple measurements and averaged them together. I dont think I could have done much else to make it more accurate, except use a more precise measuring unit for time or distance, which I do not currently possess.
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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 toy car gained speed as it descended the slope, and although not by much, the car should still be gaining speed for as indefinitely as the slope continues. Given the small units of measurement used in this experiment, combined with the likelihood of human error, making a calculation of speed from one centimeter to the next would be very difficult without more precise measuring equipment. If I were to make a video like in some of the previous assignments, I could frame by frame the action and perhaps gain more info. The toy car moved at the speeds averaged in the previous question.
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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:
The object began at rest with no speed, as it descended the slope, it gained speed up to about 17.9 centimeters per second, or one centimeter every 0.05 seconds. This was the average speed because it reflects the measurements of the car as it travelled the entire length. This data alone would not be sufficient enough to determine the cars acceleration, to the best of my knowledge I would need more to calculate its ending 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:
Given the time and proper resources I would conduct an experiment that would allow me to measure small increments of distance, such as each particular centimeter, with a more precise timer. I would film the toy car rolling down the incline with a precise timer in view. I would then watch the video frame by frame and determine the speed from one increment to the next based on the clock. I am confident that in my experiments I would find the car to be increasing in speed as it descended the slope.
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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?
About an hour total.
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You may also include optional comments and/or questions.
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&#This lab submission looks very good. Let me know if you have any questions. &#