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phys 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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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:
The book used was 6th edition Physics by Giancoli ISBN 0-13-060620-0. The book was placed on the table top with 3 quarters stacked under the book to make an incline. The toy car from the lab kit was used as the object to roll down the incline and the car rolled smoothly and speed up 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:
What was measured How it was measured How accurate Measurements
Forward Time (Trial 1) TIMER program 0.00001 seconds 2.21875 s
Time (Trial 2) TIMER program 0.00001 seconds 2.21875 s
Time (Trial 3) TIMER program 0.00001 seconds 2.28125 s
How far Object Traveled Ruler 0.1 cm 22.1 cm
How high propped up end of book was Ruler 0.1 cm 0.5 cm
Length of book from quarters to other end Ruler 0.1 cm 26.0 cm
Reverse Time (Trial 1) TIMER program 0.00001 seconds 2.78125 s
Time (Trial 2) TIMER program 0.00001 seconds 2.953125 s
Time (Trial 3) TIMER program 0.00001 seconds 3.203125 s
How far Object Traveled Ruler 0.1 cm 22.1 cm
How high propped up end of book was Ruler 0.1 cm 0.5 cm
Length of book from quarters to other end Ruler 0.1 cm 26.0 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:
Using the data the average speed was 9.96 cm/s. I believe I was able to determine the object’s average speed pretty accurately by .01 decimal places. This estimation is because the length was to the 0.01 place and the time was to the 0.00001 place, therefore the answer would be to the 0.01 place.
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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 was moving at 0 cm/s at the beginning of the timed interval because it was at rest. The average speed during this timed interval was 0 cm/s also. When the object reached the lower end of the book it was moving at a greater average speed than I calculated.
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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
final speed & average speed & change in speed -ties
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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 measured the 22.1 cm along the book that the car travels and then marked off every 5.5 cm starting from 0 cm. I then let the car roll down the book and using the TIMER program documented the time (s) it took to hit each marker (5.5 cm). I repeated this 3 times and have the data below. As you can see the time it takes to travel the same distance (5.5 cm) decreases as the car travels down the book therefore indicated that the car is speeding up.
Length (cm) Time (s)
Trial 1 0 0
5.5 0.765625
11 0.421875
16.5 0.375
22.1 0.3125
Trial 2 0 0
5.5 0.890625
11 0.40625
16.5 0.390625
22.1 0.3125
Trial 3 0 0
5.5 0.984375
11 0.4375
16.5 0.375
22.1 0.28125
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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?
1 hour
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You may also include optional comments and/or questions.
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The TIMER program is not nearly as accurate as you infer.
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I can't locate your work on the first TIMER experiment, which was part of the Introduction to Key Systems assignment at the very beginning of the course. In that experiment the question of the accuracty of the TIMER comes up.
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Otherwise everything you've done here looks OK.
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