PHY 231
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.
** #$&* Your general comment **
I completely missed doing this excercise.
** #$&* Will a steeper ramp give greater or lesser time? **
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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 30 minutes and 1 hour, with a few
reporting times as short as 15 minutes or as long as 2 hours. Median time of
completion is around 45 minutes.
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.
The steeper the ramp, the less time it takes for the ball to roll down. Since
gravity is affecting it more in the direction of the bottom of the ramp as the
slope grows, the acceleration grows as well.
#$&*
If we write down the slopes from least to greatest, next to the time intervals
observed for those slopes, would you expect the time intervals to be increasing
or decreasing, or do you think there would be no clear pattern? Explain why you
think you have correctly described the behavior of the numbers in the table.
The time intervals will be decreasing. Same reason as above answer.
#$&*
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.
1.789
1.750
1.734
1.773
1.836
1.539
1.516
1.500
1.578
1.484
The first five data are the left to right times and the last five are the right
to left times.
#$&*
Now place two dominoes under the right end and repeat the process, obtaining the
time interval for each of 5 trials.
Then place the two dominoes under the left end and repeat once more.
Enter your 10 time intervals using the same format as before.
1.227
1.273
1.227
1.273
1.211
1.102
1.086
1.133
1.078
1.148
The first five data are the left to right times and the last five are the right
to left times.
#$&*
Repeat the preceding using 3 dominoes instead of 2. Enter your 10 time
intervals using the same format as before.
0.922
0.906
0.977
1.000
0.977
0.961
0.938
0.969
0.969
0.961
#$&*
Do your results support fail to support the hypotheses you stated in the first
two questions, regarding the relationship between time intervals and slopes?
Explain.
They support the hypothesis. As the slope increases, the time decreases.
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How do you think the average velocity of the ball is related to the slope of the
ramp? Explain in as much detail as possible.
The higher the slope, the higher the average velocity. The distance travelled
is the same but you are dividing by a smaller divisor, thus resulting in a
larger quotient.
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Speculate on what it is that causes the average velocity on these ramps to
change with slope.
The force of gravity is always acting downward. When you increase the slope the
force of gravity is acting more in line with the ramp thus pulling it accross
the ramp downwatd.
#$&*
How might you verify whether your speculations are indeed valid explanations?
I'm not sure.
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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?
#$&*
&#Good responses. Let me know if you have questions. &#