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PHY 201
Your 'ball down ramp' 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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A ball is timed as it rolls from rest to the end of a ramp. The slope of the ramp is varied.
Preliminary conclusions are drawn about the motion and the effect of ramp slope. A subsequent
lab exercise uses the data from this lab to reach additional conclusions.
Most students report completion times between 45 minutes and 75 minutes hour, with a few
reporting times as short as 25 minutes or as long as 2 hours. Median time of completion is around
1 hour.
Timing Ball down Ramp
The picture below shows a ball near the end of a grooved steel track (this steel track is a piece
of 'shelf standard'); the shelf standard is supported by a stack of two dominoes. Your lab
materials package contains two pieces of shelf standard; the shelf standard shown in the figure is
white, but the one in your kit might be colored black, gold, silver or any of a variety of other
colors.
If a ball rolls from an initial state of rest down three ramps with different slopes, the same
distance along the ramp each time, do you think the time required to roll the length of the ramp
will be greatest or least for the steepest ramp, or will the interval on the steepest ramp be
neither the greatest nor the least? Explain why you think you have correctly predicted the
behavior of the system.
Your answer (start in the next line):
I believe the time required will be the least for the steepest ramp as it will encourage the fastest
velocity and acceleration.
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If we write down the slopes from least to greatest, next to the time intervals observed for those
slopes, would you expect the time intervals to be increasing or decreasing, or do you think there
would be no clear pattern? Explain why you think you have correctly described the behavior of
the numbers in the table.
Your answer (start in the next line):
I believe that if the order were least steep to most steep (ramp) then the intervals would be
decreasing as the ball's velocity would be increasing and therefore take less time to travel each
consecutive slope.
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Set up the shelf standard ramp on a reasonably level table, using a piece of 30-cm shelf
standard and a single domino under the high end of the ramp. Position the dominoes so that the
last .5 cm of the ramp extends beyond the point where the ramp contacts the domino,.and do
the same in all subsequent setups.
Set the bracket on the table, touching the lower end of the ramp so that a ball rolling down the
ramp will strike the bracket..
Mark a point about 3 cm below the top end of the ramp. Place a domino on the ramp to its
high end is at this point, and place the ball just above the domino, so the domino is holding it
back. Quickly pull the domino away from the ball so the ball begins to roll freely down the
ramp. Allow the ball to roll until it strikes the bracket.
The bracket will probably move a little bit. Reset it at the end of the ramp.
Determine how far the ball rolled from release until it struck the bracket.
Now repeat, but this time use the TIMER. The first click will occur at the instant you release the
ball, the second at the instant the ball strikes the bracket. Practice until you are as sure as you
can be that you are clicking and pulling back the domino at the same instant, and that your
second click is simultaneous with the ball striking the bracket.
When you are ready, do 5 trials 'for real' and record your time intervals.
Then reverse the system--without otherwise changing the position of the ramp, place the domino
under the left end and position the bracket at the right end.
Time 5 trials with the ramp in this position.
In the space below, give the time interval for each trial, rounded to the nearest .001 second.
Give 1 trial on each line, so that you will have a total of 10 lines, the first 5 lines for the first
system, then 5 lines for the second system.
Beginning in 11th line give a short narrative description of what your data means and how it
was collected.
Also describe what you were thinking, relevant to physics and the experiment, during the process
of setting up the system and performing the trials.
Your answer (start in the next line):
2.004
1.847
1.918
2.015
1.990
1.669
1.669
1.769
1.973
1.848
The first five lines are the time intervals from the TIMER program for five trials of the ball rolling
down the shelf standard ramp with one domino under the right side of the ramp rolling towards
a bracket at the end of the ramp on the left side. The next five lines are the intervals from timing
the reverse system. As I was setting up the system, I was thinking of the various factors involved,
such as v_0 = 0cm/s, what the displacement would be, what the acceleration would be and
what the vAve would be.
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Now place two dominoes under the right end and repeat the process, obtaining the time interval
for each of 5 trials.
Then place the two dominoes under the left end and repeat once more.
Enter your 10 time intervals using the same format as before.
Your answer (start in the next line):
1.203
1.195
1.156
1.141
1.187
1.273
1.344
1.359
1.289
1.281
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Repeat the preceding using 3 dominoes instead of 2. Enter your 10 time intervals using the
same format as before.
Your answer (start in the next line):
1.008
1.008
0.955
1.078
1.008
1.008
1.039
1.001
.945
.969
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Repeat the preceding again, still using the 3 domino setup, but this time place a CD or a DVD
disk (or something of roughly similar thickness) on the 'low' end of the ramp. You need time only 5
intervals, but if you prefer you may use 10. Enter your 5 (or 10) time intervals using the same
format as before.
Your answer (start in the next line):
1.023
1.008
1.125
1.094
1.078
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Repeat the preceding one last time, still using the 3 domino setup, but remove the disk and
replace it with a piece of paper. You need time only 5 intervals, but if you prefer you may use
10. Enter your 5 (or 10) time intervals using the same format as before.
Your answer (start in the next line):
.992
1.029
1.002
1.008
1.017
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Do your results support or fail to support the hypotheses you stated in the first two questions,
regarding the relationship between time intervals and slopes? Explain.
Your answer (start in the next line):
I believe my results support the hypotheses that I stated in the first two questions because the
interval results got shorter the steeper the slope of the ramp. With only one domino my results
were close to 2 second intervals. This diminished to the point of using three dominos my intervals
wer below 1 second.
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How do you think the average velocity of the ball is related to the slope of the ramp? Explain in
as much detail as possible.
Your answer (start in the next line):
vAve is equal to the change in position over the change in clock time. The displacement of the
ramp is equal in all three slopes, a 30cm piece of shelf standard marked 3cm down equals a
total displacement of 27cm. As the slope of the ramp increases, the clocktime decreases which
would increase the vAve for each subsequently steeper ramp. Let's say the average `dt for one
domino ramp was 1.9sec. The vAve would be 27cm/1.9sec = 14.2cm/s. If the `dt of the two
domino ramp was 1.3sec then the vAve would be 27cm/1.3sec= 20.8cm/sec. This would
continue as the steepness of the ramp increased.
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Speculate on what it is that causes the average velocity on these ramps to change with slope.
Your answer (start in the next line):
I would speculate that the force (gravity) that keeps the ball still on a level ramp would work to
pull the ball towards the low end of the ramp as the ramp slope is increase due to the fact that
the force is now not just under the ball at rest, but also pulling from the low end of the ramp. The
vAve would increase as the ramp increases because the drag that is created by the pull of
gravity under the surface of the ramp becomes less than the pull of gravity at the low end of the
ramp.
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How might you verify whether your speculations are indeed valid explanations?
Your answer (start in the next line):
If I had access to a zero gravity room, I could retry the experiment with a non-conductive ramp
and use a steel ball with magnets, one under the steel ball at rest at one end of the level ramp
(far enough below to just hold the ball at rest, and a second at the end of the ramp (far enough
away to not overcome the pull of the first magnet in a level position). Then I would conduct the
experiment above each time increasing the slope of the ramp without changing the position of
the ramp. I believe this would show that as the force of the first magnet weakens, the ball would
be influenced by the pull of the second.
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This is a very interesting idea.
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Do your data conclusively show that the disk made a difference?
Your answer (start in the next line):
vAve_1d= 27cm / 1.87s =14.44cm/s
vAve_2d= 27cm / 1.24s =21.77cm/s
vAve_3d= 27cm / 1.00s =27.00cm/s
vAve_CD= 27cm/ 1.07s = 25.23cm/s
As my calculations above show, the CD disk did have an effect on the vAve of the ball as the
ramp was not as steep as the 3 domino ramp.
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Do your data conclusively show that the piece of paper made a difference?
Your answer (start in the next line):
vAve_paper= 27cm / 1.01s = 26.73cm/s
vAve_3d= 27cm / 1.00s =27.00cm/s
As the above calculations show, I don't believe there is a conclusive difference made by the
paper. The discrepency at the level of change of slope is (I believe) less than human error in
timing the release and finish of each run.
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Imagine that someone is placing different objects below the 'low' end of the ramp, and you are
timing the ball. Assume that somehow the object placed below the 'low' end is hidden from you
in a way that does not interfere with the timing process. Compared to the thickness of the DVD,
how thin would the object have to be before you would be unable, using the TIMER, to observe
a difference in times down the ramp?
Answer this question in the first line below. Express your answer in multiples or fractions of the
thickness of a disk.
Starting in the second line, explain how you came to your conclusion, based on the results you
obtained in this experiment. Also discuss how you could modify or refine the experiment, still
using the TIMER, to distinguish the effect of the thinnest possible object placed under the 'low end.
Your answer (start in the next line):
I think the object would have to be at least .3 or .4 mm thick for me to accurately discern a
difference.
I used a piece of copy paper that without a micrometer I can only guess is .1 mm thick. The disk
I used was about 1.25 mm thick, and the dominos were 9mm thick. The CD was 1.25 / 9 the
thickness of the domino and had a `dv of 1.77cm/s. I believe if I were to use an assistant to
release the ball so that I could concentrate solely on timing the experiment, I would be able to
come up with more accurate vAve. I could then use a stack of paper the same thickness of the
CD and remove one sheet after several trials. By calculating the average velecity over the
course of these trials I believe a resonably accurate number could be given for the amount
velocity changes with each piece of paper until no noticeable change is detected.
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Had you placed the disk below the 'low' end of the ramp in a 1-domino setup, do you think the
difference in times would have been greater or less? Do you think you would be better able
distinguish the presence of a thinner object using the 1-domino setup, or the 3-domino setup?
Explain your reasoning below:
Your answer (start in the next line):
The difference of a thinner object under the three domino ramp would be more noticeable by
1/3 than the one domino ramp because the the three domino ramp is 3 times the height of the
one domino ramp.
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Does the ball's velocity change more or less quickly with the 3-domino setup or the 1-domino
setup? Explain as best you can how you could use your results to support your answer.
Your answer (start in the next line):
The 3-domino setup incurs the quicker velocity change than the 1-domino change. For both
setups, the v_0 = 0. vAve_1d= 27cm / 1.87s =14.44cm/s, vAve_3d= 27cm / 1.00s =
27.00cm/s.
`dv_1d = 14.44cm/s - 0cm/s = 14.44cm/s
`dv_3d = 27.00cm/s - 0cm/s = 27.00cm/s
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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?
Your answer (start in the next line):
2 hours.
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&#Very good data and responses. Let me know if you have questions. &#