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PHY 121
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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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):
Steepest ramp-least time. I believe that the increased slope of the ramp will cause the
ball to go faster.
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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):
Slopes from least to greatest will produce times from greatest to least. This is
because I believe that the slope of the ramp will affect the times and the the more of a
slope there is, the faster the ball will roll.
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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):
1.891
1.887
1.906
1.945
1.934
1.816
1.934
1.770
1.922
1.879
The data tells how long it took the ball to roll the length of the ramp. It was
collected by making a starting mark on the ramp and timing the ball's trip down the
ramp. I felt better about my results on this because it gave me time to get ready
between clicks. I had some difficulty with the ball not wanting to roll, so I chose a
different ball from the kit, and it worked out well. I'm also assuming that moving the
ramp so that the ball is going right to left as well as left to right, is because the
table top might not be as even as I think.
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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):
1.402
1.359
1.305
1.457
1.254
1.230
1.320
1.367
1.305
1.242
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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):
1.016
1.047
.9766
.9727
1.082
1.000
1.008
.9883
1.047
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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
1.129
1.031
1.063
1.086
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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):
.969
.973
.965
1.023
1.051
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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):
My results support the hypotheses that I stated in the first two questions. The steeper
the slope (higher the ramp), the shorter the speeds. The data for the 1-domino ramp
ranges from 1.77 s-1.945 s. When I added one domino, the range changed to 1.230-1.457,
which is less time. When I added another domino, the overall elapsed time dropped again
to between .9727 s and 1.082 s.
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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):
I believe that the velocity is related to the slope of the ramp because that is the only
thing that we changed in the experiment. The length of the ramp is the same. The ball
is the same. The starting point is the same. The only thing that changed was the slope
of the ramp and with each additional domino added to increase the slope, the length of
time dropped.
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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 think that gravity is pulling on the object. If you drop something straight
down, it accelerates at a rate determined by gravity. If you try to roll something
horizontally, the gravity is pulling down on the object. Each time the slope of the
ramp increased, I think that the effect of the pull of gravity increased as well.
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How might you verify whether your speculations are indeed valid explanations?
Your answer (start in the next line):
I am unsure how you would prove that the reason that gravity is the reason an increase
in slope results in faster velocities. You could, however, test higher slopes to see
what the change is velocity would be and compare it with a drop/free fall from rest.
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Do your data conclusively show that the disk made a difference?
Your answer (start in the next line):
The data do confirm that the disk made a difference. The range without the disk was
.9727 s-1.082 s. With the disk the range was 1.0234 s - 1.1289 s.
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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 data do not conclusively show that the piece of paper made a difference. Without
the paper, the range was .9727 s - 1.082 s With the paper, it was .9687 s - 1.0407 s.
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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 believe that half the thickness of a disk would have an impact on results.
I stacked up papers beside the disk. There were about 18 sheets of paper that had about
the same thickness as the disk. Then I just started feeling the thickness of different
amounts of paper to see when I thought that there would be a measurable difference. It
was about half of the papers. You could start with one sheet of paper and run 5 trials.
Then add one more sheet at a time and run 5 more trials to see when the results seem to
be affected.
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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 think that the effect of placing the disk on the low end of the ramp in a one-domino
set up would have had a greater effect on the times. This is because it looks like a
domino is about 6 disks in thickness. You would have reduced the slope by about 1/6.
But, if you were using it with three dominos you would be reducing the slope by about
1/18.
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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 ball's velocity seems to change more quickly with the three-domino setup. I think
this because when the ball reached the bracket on the one-domino set up, it clunked into
the bracket but the bracket usually didn't move much. When the ball hit the bracket on
the 3-domino set up, it always moved it out of place by about a centimeter. This means
that it had more force at that point. You could mark mid-way on the ramp and measure
the times on top and bottom of the ramp with both 1- and 3- domino set ups.
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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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*#&!
&#Very good data and responses. Let me know if you have questions. &#