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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:
Book: The Dash Diet for Weight Loss, ISBN 978-1-4516-6936-7
Object: Small styrofoam spool of thread with thread on it; diameter approx 22 mm, width
approx 28 mm
Prop: 3 quarters, approx 5.5 mm when stacked
The spool took a short time to pick up speed. Sometimes it started, slowed down a
little, and then picked up speed again. Depending on how I placed the spool on the
book, it either went straight down the book, or slightly off to the right or left. I
found it difficult to start the timer at the same time that I was starting the spool
because it sometime didn't get started right away or stuck to my finger. The spool
rolled fairly well. Except as noted below, it sped up smoothly. It did not always go
straight down the book, also as noted below. I actually tested several objects before I
found one that did roll fairly well down the book.
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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:
1 2.269531 Round 1-Went approximately 217 mm, rolled slightly diagonally
2 1.945313 Round 2-went approximagely 215 mm, rolled straight
3 2.402344 Round 3-went approximately 215 mm, rolled straight, but had a little
pause right after it got started
4 2.175781 Round 4-went approximately 215 mm, rolled straight
Changed sides:
5 1.894531 Round 1-went approximately 217 mm, rolled slightly diagonally
6 1.195313 Round 2-went off the side about mid-way down the book, approximately 150
mm
7 1.671875 Round 3-went straight approx 215 mm
8 1.898438 Round 4-went slightly diagonally approx 217 mm
I held the spool of thread on the book and measured from the edge of the spool to the
edge of the book and got 215 mm. This is not necessarily accurate because I don't know
for sure if I placed the spool at that exact spot every time. I also measured from that
spot to the edge at the slight diagonal that the spool took. Again, it is not
necessarily accurate because I am not positive of the exact placement of the spool at
the beginning and if the angle was the same each time.
I did notice that the first 4 trials going from left to right in front of me were
slightly longer times than the measurement of the 4 trials after I turned the book
around and the spool was starting right and going toward the left. I did a few more
trials each way, and found that the spool seemed to move faster going from right to
left. I'm assuming that means that there is a slight dip in the table at that point
which causes the angle of the book to be slightly greater.
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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 average final speed of the spool of thread was: 95.6 mm/sec; 110.5 mm/sec; 89.5
mm/sec; 99.8 mm/sec for the first side and 114.5 mm/sec; 125.5 mm/sec; 128.6 mm/sec;
114.3 mm/sec for the second side.
I would not vouch for the accuracy of the data at this point because I do not feel that
I am any kind of expert on using the timer accurately. I would not swear that I always
got it started and stopped perfectly. Also, the length is not exact. As I was doing
the experiment, I was thinking that it would be nice to have a way to mark the exact
path of the object each time it was released. That way I would be more certain of how
long the path was. What it did show, I believe, was that the table must not be as flat
as I had thought because the second side had obviously shorter times than the first.
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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 always started at zero. For the most part, the spool picked up speed fairly
smoothly and was moving at more than the average speed (at it's maximum velocity) when
it got to the lower end of the book. The average speed (average of all 4 trials for the
first round) was 98.85 mm/sec. The average speed (average of all 4 trials for the
second round) was 20.725 mm/sec.
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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:
Least: initial speed of 0 mm/sec.
Average speeds: 44.75 mm/sec
47.8 mm/sec
49.9 mm/sec
55.25 mm/sec
57.15 mm/sec
57.25 mm/sec
60.36 mm/sec
62.75 mm/sec
64.3 mm/sec
Final speed: 89.5 mm/sec
95.6 mm/sec
99.8 mm/sec
110.5 mm/sec
114.3 mm/sec
114.5 mm/sec
125/5 mm/sec
120.725 mm/sec
128.6 mm/sec
I am not sure how to determine change in speed from this data, just from observation.
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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 took the same book and drew a starting line across the top and 21 cm from the bottom
of the book. Then I drew a line that was parallel to that line 10.5 cm from the bottom
of the book for my mid-point. I used a stop watch to time how long it took for 4 trials
using the same spool of thread and timed it from the starting line to the middle of the
course. The times were: 1.86 sec; 1.51 sec; 1.34 sec; and 1.67 sec. Then I started
the spool at the starting line but did not start timing until it hit the middle line.
These times were: .65 sec; .83 sec; .73 sec; and .79 sec. This showed me that it look
more than 1.5 seconds but less than 2 seconds to get from the starting line across the
10.5 cm line. However, it look less than a second to get from the mid-point of the
course to the edge of the book.
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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?
This took about an hour and a half. This time includes both conducting the experiment, analyzing the data, and writing the answers.
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You may also include optional comments and/or questions.
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&#Your work on this lab exercise looks good. Let me know if you have any questions. &#