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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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9/18/11 10:45 pm
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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 the Physics book by Giancoli, 6th edition. The ISBN number is 9780131846616.
The object I used was an almost empty bottle of allergy medicine.
To prop the object up I used a thin piece of wood.
The object rolled smoothly, sped up as it went down the incline, and 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:
I timed how long it took for the bottle to travel the length of the book, measured the distance the bottle traveled, measured how much higher the book was on one end than the other, and measured how the far end of the book was from the propped end of the book.
I believe the measurements were fairly accurate and within 0.2 cm. I believe the timings were accurate within a quarter of a second.
First Timings:
2.5 seconds
2.5 seconds
2.6 seconds
Reverse Timings:
2.3 seconds
2.7 seconds
2.5 seconds
Distance object traveled: 25.4 cm
Difference of height from one end of book to other: 1.11 cm
Distance of end of book from propped end: 29.21 cm
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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:
2.5+2.5+2.6+2.3+2.7+2.5 = 15.1/6 = 2.52 seconds
25.4 cm/2.52 sec = 10.08 cm/sec
My accuracy for the average speed is limited by my accuracy for the timings and the distance. I believe my accuracy is within 2 cm/sec.
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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 begins at 0 cm/sec.
Its average speed was 10.08 cm/sec.
The object was moving at a greater speed than the average speed I calculated at the lower end of the book because by the end, the object’s speed had increased.
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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 & change in speed = tied
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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 same materials as in my first experiment, except for this experiment I timed how long it took to get from the starting point to the midway point on the book. I then timed how long it took to get from the midway point to the end of the book when the object started at the top of the book. This way, I could see if the object was speeding up as it rolls down the incline (which is the second half of the book).
Starting point to midway point (distance 12 cm):
1.1 sec
0.98 sec
1.3 sec
Midway point to end point (distance 12 cm):
0.94 sec
0.94 sec
0.97 sec
Average time for starting point to midway point:
1.1+0.98+1.3 = 3.38/3 = 1.13 seconds
Average speed for starting point to midway point:
12 cm/1.13 sec = 10.65 cm/sec
Average time for midway point to end point:
0.94+0.94+0.97 = 2.85/3 = 0.95 seconds
Average speed for midway point to end point:
12 cm/0.95 sec = 12.63 cm/sec
The average speed for the midway point to the end point is faster than the average speed for the starting point to the midway point. This indicates that the bottle’s speed is increasing as it rolls down the incline.
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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 1 ½ hours.
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&#Very good data and responses. Let me know if you have questions. &#