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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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September 14, 2011 at 9:37 p.m.
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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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Book - About Philosophy, Tenth Edition - ISBN No. 0-205-64518-6 - object traveled the distance of about 23 cm
Object - Empty travel tube of Dramamine - NDC 50580-313-12 - 12 count - empty - with lid on.
Prop - Book was propped up on two legal pads - with a height of about 7 mm
Roll - The object rolled smoothly. However, I left the lid on and always north of me on release. This caused the roll to slightly veer inward each time.
Speed - The object sped up as it rolled down the book.
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:
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I measured the amount of time it took the above stated object to first travel in a right to left direction, with the 23 cm surface which was traveled being propped up on its right side to an elevation of 7 mm. Three consistent times obtained when the object was released from about the same point starting from rest were:
RESULTS A
1) 1.5
2) 1.507813
3) 1.507813
Now with the object traveling the same specifications only this time in a left to right direction with the propped up side being the left the times were less consistent. This occurred on the table as well initially so for these times and the times above I performed the experiment on the floor. I suppose my floor is just not even because here is my measurements.
RESULTS B
1) 2.328125
2) 2.453125
3) 2.382813
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:
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RESULTS A AVERAGE
Average time when combining results and dividing by 3 = 1.5052 sec.
Average speed = 15.2804 cm/sec. * 60 sec/1 min. * 60 min/1hr * 1m/100cm * 1km/100m = 5.5009 km/hr
RESULTS B AVERAGE
Average time when combining results and dividing by 3 = 2.3880 sec.
Average speed = 9.6315 cm/sec * 60 sec/1 min. * 60 min/1hr * 1m/100cm * 1km/100m = 3.4673 km/hr
Given the variances in the time of Result A I would guess it would be within .01 of the km/hr because that is how close the average times were.
Results B would be less accurate because the times were not as consistent so I would say between .1.
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:
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The object began at rest in both examinations, therefore the speed was 0 at both times.
Since the speed calculated was an average, and since the object began at 0 and obviously built up speed to begin moving, the object had to have been going faster at the end due to its acceleration.
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:
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Objects initial speed, change in speed, average speed, and final speed.
They tie together because it is traveling downhill the start will be the least, the change builds up to the final in increments so it will be less than the average, the average the gap between initial and final determined by the increase, and the final is greatest because its the final result.
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:
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First I would repeat all steps from the previous assignment. However, here I do not begin my timer until the object reaches the midpoint of the book.
I place a paper clip on the book at 11.5 cm and begin the timer once the object passes that point and stops at the end.
Here are side by side the results from the previous on the left which include total time, and the second half on the right
RESULTS A
1) 1.5 1) .57091
2) 1.507813 2) .5625
3) 1.507813 3) .5703125
RESULTS B
1) 2.328125 1) .8046875
2) 2.453125 2) .765625
3) 2.382813 3) .9140625
Here, again you can clearly see that the first half of the objects travel takes nearly twice the time as the second half, indicating this object is speeding up.
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?
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1 hour and 19 minutes
You may also include optional comments and/or questions.
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&#Your work on this lab exercise is good. Let me know if you have questions. &#