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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.
#$&* Your general comment **
09/25/2011 4:05 PM
#$&* Will a steeper ramp give greater or lesser time? **
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 think the time will be the least for the steepest
ramp because the closer the ball gets to vertical the
less there is to interfere with it’s descent.
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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):
The time intervals would be decreasing as the slopes
increased because the marble would be traveling the
distance of the ramp faster as the slope increases.
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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):
1.73 s
1.75 s
1.75 s
1.66 s
1.73 s
1.80 s
1.67 s
1.75 s
1.67 s
1.71 s
The times above, measured in seconds, were the times it
took the ball to roll down an inclined ramp. The first
five were from the ball rolling to the left and the
second five were from the ball rolling to the right.
The ramp was elevated by a domino lying flat and the
distance was approximately 27 cm. While recording the
times I tried to be as precise as I could with the
measurements of the ramp and the placement of the ball.
I was also thinking about how the incline may affect the
acceleration of the ball.
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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):
1.09 s
1.14 s
1.11 s
1.11 s
1.17 s
1.19 s
1.22 s
1.22 s
1.22 s
1.18 s
The times above, measured in seconds, were the times it
took the ball to roll down an inclined ramp. The first
five were from the ball rolling to the left and the
second five were from the ball rolling to the right.
The ramp was elevated by two dominos lying flat and the
distance was approximately 27 cm.
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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):
.86 s
.88 s
.89 s
.83 s
.94 s
.93 s
.92 s
.88 s
.87 s
.95 s
The times above, measured in seconds, were the times
it took the ball to roll down an inclined ramp. The
first five were from the ball rolling to the left and
the second five were from the ball rolling to the right.
The ramp was elevated by three dominos lying flat and
the distance was approximately 27 cm.
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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):
.89 s
.88 s
.90 s
.90 s
.93 s
The times above, measured in seconds, were the times
it took the ball to roll down an inclined ramp. The
ramp was elevated by three dominos lying flat on the
high end and a compact disc on the low end, and the
distance was approximately 27 cm.
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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):
.92 s
.98 s
.88 s
.87 s
.93 s
The times above, measured in seconds, were the times it
took the ball to roll down an inclined ramp. The ramp
was elevated by three dominos lying flat on the high end
and a piece of paper on the low end, and the distance
was approximately 27 cm.
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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):
The results support my hypothesis. As the slope
increased the times decreased.
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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):
The average velocity of the ball is seems to be
directly proportional to the slope of the ramp. As the
slope increases the time decreases. If the time
decreases and the distance remains constant the average
velocity must be increasing.
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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):
As I stated earlier I believe as the slope approaches
vertical there is less friction to act upon the ball.
This in turn allows the ball to get closer and closer to
its terminal velocity.
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How might you verify whether your speculations are
indeed valid explanations?
Your answer (start in the next line):
I could keep increasing the slope of the ramp until it
reached a point approaching vertical. The time
intervals should keep getting shorter and shorter.
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Do your data conclusively show that the disk made a
difference?
Your answer (start in the next line):
The mean time for three dominos incline was .895
seconds. The mean time for three dominos and a disc was
.90 seconds. If the time measurements were extremely
precise I would say the disc made a difference, as it
stands I would have to say there is not enough
difference in the average time intervals to say
conclusively the disc made a difference.
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Do your data conclusively show that the piece of paper
made a difference?
Your answer (start in the next line):
The mean time for the set up with a piece of paper was
0.916. If my time measurements were extremely precise
this would suggest the paper made a bigger difference
than the disc, but I suspect my measurement were far
from precise because as the earlier data suggest the
time interval should have decreased with the paper
versus the disc, not increased.
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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 would say the thickness of 1/2 disc would be
measurable. My results showed some difference between
the set up with the disc and the set up without the
disc. A more precise set up for recording the time
interval might include a photo electric eye on the top
of the ramp to start the timer and a sound sensitive
device at the bottom to stop the timer.
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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):
I believe the time difference with a CD would have been
more drastic on the one domino incline because the
velocity of the ball was much lower. Because the
momentum of the ball was much lower on the one domino
incline the thickness of the CD would have had more
affect on the time because it would have made the slope
closer to horizontal therefore slowing the ball much
more than the steeper inclines of two or three dominos.
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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 velocity changes more quickly with the three domino
setup. The times on the flatter incline are greater
than the steep incline. This suggests the acceleration
is greater on the steep incline. As acceleration
increases the change of velocity also increases at a
greater rate.
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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):
1 hour and 15 minutes.
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*#&!
&#This lab submission looks very good. Let me know if you have any questions. &#