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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.
#$&* Your general comment **
10/30/11 5:53pm
#$&* 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):
The time required for the ball to roll down the ramp will be the shortest for the steepest ramp and the longest for the flattest ramp because the ball will accelerate faster on a steeper ramp.
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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):
If we write down the slopes from least to greatest, the time intervals corresponding to those slopes will be decreasing because the times will be getting less as the ramps become steeper.
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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):
1.957s
1.984s
2.066s
1.805s
1.863s
2.199s
2.176s
2.258s
2.159s
2.242s
I set up the track raised on one end the height of a domino and timed how long it took the ball to roll down the track and strike the bracket at the bottom of the track. I measured the length of track that the ball would roll down and it was 27.5cm. I measured five trials and then switched the raised track to the other end and measured five more trials. I assumed the times would be very similar because I had the track setup up on a table that appears level. My measurements suggest that the first orientation of the track was slightly steeper than the second because the times are slightly faster.
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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):
1.320s
1.340s
1.289s
1.289s
1.332s
1.473s
1.504s
1.465s
1.488s
1.496s
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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):
1.227s
1.141s
1.035s
1.063s
1.098s
1.184s
1.238s
1.168s
1.199s
1.199s
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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):
1.219s
1.148s
1.190s
1.209s
1.117s
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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):
1.125s
1.137s
1.066s
1.105s
1.105s
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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 my earlier hypothesis because as the ramp gets steeper, the times are getting less.
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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 changes as the slope of the ramp changes. As the ramp gets steeper, the average velocity of the ball gets greater.
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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):
The average velocity of the ball gets greater as the ramp gets steeper because the acceleration increases as the ramp gets steeper.
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How might you verify whether your speculations are indeed valid explanations?
Your answer (start in the next line):
You could calculate the average acceleration for each different slope of the ramp to see that the average acceleration increases as the ramp gets steeper.
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Do your data conclusively show that the disk made a difference?
Your answer (start in the next line):
Yes, the times with three dominoes under one side of the ramp and nothing under the other side are less than the times with three dominoes under one side and a cd case under the other side showing that changing the angle of the ramp to make it less steep slowed down the ball.
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Do your data conclusively show that the piece of paper made a difference?
Your answer (start in the next line):
No, the measurements are not accurate enough to show conclusively that a piece of paper under the bottom side of the ramp slowed down the ball.
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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):
1/2 the thickness of the cd
I think I could distinguish if there was an object under the low side of the ramp with three dominoes under the high side of the ramp down to a size about half as thick as the cd. The average time with three dominoes under the high side and nothing under the low side is 1.155s and the average time with three dominoes under the high side and a cd under the low side is 1.177s. The difference is 0.002s and I think I can use the timer program somewhat accurately to about 0.001s which would be roughly the time difference with an object of half the cd’s thickness under the low side of the ramp.
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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 in times would have been greater if I had placed a cd under the low side of the ramp with only one domino under the high side of the ramp because these would have been less steep ramps so the times would have been longer and a larger difference between times when placing an object under the low end of the ramp. I would have been able to distinguish the difference that an object under the low side of the ramp makes better in the one-domino setup than the three-domino setup.
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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 three-domino setup than the one-domino setup because the acceleration is increased, as the ramp gets steeper. My results show this because the times are much shorter for the three-domino setup than for the one domino setup.
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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 ½ hours
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*#&!
&#Very good data and responses. Let me know if you have questions. &#