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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.
** Initial Timing Experiment_labelMessages **
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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:
I used the Giancoli Physics sixth edition for my book. I used a white ball from the lab
kit. The ball is approximately 14mm in diameter. The length of the roll was 270mm. To
prop the book on one end I used one domino from the lab kit positioned so that its
thickness of approximately 10mm was propping one end of the book. The ball appeared to
speed up going down the ramp. It did not roll in an exact straight line, but it was
fairly straight.
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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:
In this experiment the time was measured for a 14mm diameter ball to roll a distance of
270mm down an incline of 10mm over the 270mm distance. The timer program was used to
measure time and the start and stop of the clock was visual through my finger to the
mouse button. The time was accurate to about 0.1 second. When the book and incline were
rotated 180 degrees all distance measurements were the same. The time data is as
follows:
Test 1 times in seconds:
1.83
1.58
1.68
Test 2 times in seconds(180 degree rotated);
1.65
1.65
1.65
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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:
For each test run the average time of the three samples is used.
Using the formula ‘ds=vAve*’dt and arranging to solve for vAvewe find for the tests:
Test 1: vAve=’ds/’dt=278mm/1.70s=163.53mm/s
Test 2: vAve=’ds/’dt=278mm/1.65s=168.53mm/s
The accuracy of the velocity estimate is probably around 5mm/s. Our two tests are 5mm/s
apart. Given that the angle was no different on each test the average velocity should
remain the same. It is possible the desk the book was sitting on was not level, which
would cause a different speed when the incline was rotated 180 degrees.
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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:
At the beginning the object was stationary.
Average speed was about 168.48mm/s.
At the lower end of the book the speed is greater than the average speed I calculated.
If the object in motion starts at a stand still, the average speed has the slow speed at
the start involved in the calculation. Therefore, to overcome this under average speed
at the beginning there must be an over average speed at the end.
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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 is 0mm/s
Average speed is 168.48mm/s
Final speed is greater than average 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:
The experiment design to get data to prove acceleration was to mark the incline at the
half way point and record times for the first half vs the second half. After several
sample timing runs, three sample timing runs were recorded, moved to Excel and averages
for the first half of the incline and the second half of the incline were calculated.
1 16888.56 16888.56 half
2 16889.57 1.015625 1
3 16890.07 0.5 2
4 16897.5 7.421875
5 16898.39 0.890625 1
6 16898.75 0.359375 2
7 16903.9 5.15625
8 16905.01 1.109375 1
9 16905.53 0.515625 2
The column on the right is for the time for first part or second part of the incline. It
is clear that the second part of the incline is faster due to the shorter time and equal
distance. The calculated average time is 1.00 seconds for the first half and 0.46
seconds for the second half. Plugging this data into the ‘ds=vAve*’dt formula and we
have:
First half incline vAve=’ds/’dt=139mm/1.00s=138mm/s
Second half incline vAve=’ds/’dt=139mm/0.46s=302mm/s
The first half vs second half vAve data proves that there is acceleration because second
half is faster than first half. It also proves that the speed at the end is faster than
the vAve calculated for the entire length of 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?
One hour.
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You may also include optional comments and/or questions.
Is this formatted correctly for you? I did this in Word, then copy paste to Notepad.
However, it looks like the questions and answers run together.
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Very well done.
The format is fine for me.
Be sure you can read the document OK.
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