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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:
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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:
The book used is the physics book we are using for the class- ISBN 9780130606204, its rather thick so I had to use a few more quarters to prop it up with. I used 6 quarters on the end to prop the book up.
The measurements I took includes: the time it took for the car to roll from one end to the other (3 measurements), the distance the car traveled while the timer was active,
The amount of height difference between one end of the book vs the other. I did all these measurements by hand using a ruler and the TIMER program, the ruler was propped up in the background on the book to help record distance vs time measurements.
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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 three timer intervals I recorded were 1.304688, 1.296875, and 1.265625, which appears uniformal. The length of the book and distance the car needs to travel is approximately 10.5 inches (set long-way)
I hit the timer right before the car fell off the edge, which started around when it had approximately 1.5 inches left of distance to travel.
For my measurements, I found that the car moved 9 inches before it reached the end of the ramp and fell off (this is accounting for the cars own length)
The car was moving at 9 inches per 1.3 seconds. I believe this is an accurate measurement due to the technique and method I used to determine the distance traveled by the car during the experiment.
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9 inches per 1.3 seconds does imply the average velocity, but the average velocity would be in inches per second, not in inches per 1.3 seconds.
You can easily figure out the average velocity in inches per second. What do you get?
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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:
I'm going to make a measurement within one inch for the beginning of the timed interval. I can say that the object is traveling 9 inches altogether, and is taking 1.3 seconds to travel this distance.
Dividing 9 by 1.3 gives me 0.14 which I believe is the average speed during the beginning interval. By the time the object reached the end of the book, it had gained momentum and as a result was traveling at a faster speed.
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If you divide 1.3 by 9 you get 0.14.
However this is not what you get when you divide 9 by 1.3.
The quantities have units. 1.3 has units of second, 9 has units of inches.
So the question is, what do you get (the number and the units) when you divide 9 inches by 1.3 seconds, what do you get (the number and the units) when you divide 1.3 seconds by 9 inches, and which would be the velocity?
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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. The initial speed was slow due to the amount of momentum that was stored; almost none. During the middle of the descent the car had a fair amount of momentum, and
at the final moments it had stored the more momentum than before due to 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:
Gravity pulling on the mass of the object created a momentum that was built over time, as by the time the car reached the end of the book, it had gained much more momentum than it had started with and therefor was traveling at a higher rate of speed than its initial moments.
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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 40 minutes
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Good, but you do need to make some revisions.
&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes. &#
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