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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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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):
The time required to roll the length of the ramp will be least for the steepest ramp, the increased slope will cause stronger forces of gravity to be exerted on the ball and it will accelerate 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):
The time intervals would be decreasing. As the slope greatens the time interval becomes smaller.
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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):
1.672
1.742
1.703
1.625
1.625
1.945
2.062
1.977
1.922
2.015
I obtained the measurements by using the assigned method above. The desk on which I am performing this experiment must be angled slightly too account for the increase in time interval once the system was reversed. This makes me think of our change in velocity and our change in time, with relevance to the slope as well as the rise and runs. I can now better visualize what this data would look like on a graph.
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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):
1.265
1.172
1.188
1.117
1.109
1.312
1.25
1.312
1.343
1.476
The numbers above represent the measurement of the time intervals for the slope of two dominoes. The intervals have gotten smaller, the latter set of 5 numbers are a little longer like before.
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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):
.945
.867
.835
.937
.859
1.117
1.054
1.101
1.054
.961
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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):
I used a domino instead of a cd/dvd
1.101
1.117
1.125
1.093
1.085
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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):
.906
.937
.890
.945
.976
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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):
Yes, the greater the slope the shorter the time interval. The cd/dvd (in my case domino) gave the ramp a lesser slope, which corresponded to a longer time interval. The piece of paper that gave the ramp a greater slope than the domino corresponded to a shorter time interval.
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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 initial velocity will be the same as will the change in position, the final velocity will differ based on the steepness of the slope, as would the change in position with respect to clock time, which is average velocity.
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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):
On a greater slope the final velocity is higher, giving us a larger overall average velocity.
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How might you verify whether your speculations are indeed valid explanations?
Your answer (start in the next line):
Plotting our results as data points on a graph would allow us to most properly infer whether or not our hypotheses are true.
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Do your data conclusively show that the disk made a difference?
Your answer (start in the next line):
In my case I used a domino, but yes regardless the object placed at the low end will make a difference. The greater the object’s height the smaller the slope and the longer the time interval.
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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 difference would not be measureable with the current systems we are using but according to our data so far, we can conclude that any object that adjusts the slope of the rail ultimately adjusts the time interval. The paper, even in its minute thickness still would have an effect on the results.
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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):
If the cd altered the time interval to a one hundredth of a second 0.01 at a thickness of 1 cm, half of 1cm would alter the time interval to 0.0001, which would be increasingly less accurate with our timer program. These measurements are only estimates, but this is the best process I can think of to use to determine just how low we can really go.
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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 1 domino setup would have been easier simply because the ball is rolling slower giving our eyes better judgment for when to click the timer program. The interval would certainly increase with consecutively thicker objects placed at the low end of the ramp. Determining how much the paper altered the interval will depend on how accurately the timer program measures it, which we’ve learned the timer program is good to about 0.001. If the piece of paper accounts for less a difference than that, we will not be able to accurately pinpoint numerically the difference.
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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 changes more quickly with the 3 domino setup, which corresponds to our graph of velocity vs clock time, in which the slope is our acceleration. A steeper slope will account for a quicker acceleration.
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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):
About two hours
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*#&!
&#Your work on this lab exercise looks very good. Let me know if you have any questions. &#