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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):
Steepest ramp will be shortest time. This is because the acceleration will be the greatest on the steepest 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):
The time intervals will decrease as the ramp slope increases. Since there will be more acceleration in the higher ramp slopes, the time to travel a set distance will be shorter.
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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):
2.156
2.141
2.141
2.188
2.125
2.219
2.266
2.281
2.281
2.281
The above data shows that there was a difference of about 0.1s between the two ramp positions. This seems odd, since everything seemed the same except to rotate the ends of the ramp. The first 5 samples averaged 2.150s and the second 5 samples averaged 2.286s for an average difference of 0.116s.
Relative to physics I’m thinking I have ‘ds, ‘dt. From ‘dt and ‘ds I can find vAve. I also know that v_0=0, so I can now solve for v_f = 2* vAve. Now I have ‘dv. Now that I know all that I can solve for aAve=’dv/’dt.
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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):
1.344
1.406
1.344
1.406
1.328
1.421
1.422
1.422
1.391
1.391
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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):
1.125
1.141
1.109
1.125
1.109
1.141
1.172
1.156
1.172
1.172
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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):
1.141
1.156
1.188
1.172
1.188
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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):
1.141
1.156
1.156
1.156
1.141
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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 data supports my hypothesis that the steeper ramp will have the shortest time.
With one domino ‘dt was about 2.2s
With two dominoes ‘dt was about 1.4s
With three dominoes ‘dt was about 1.2s
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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):
Since vAve=(v_f+v_0)/2 for uniform accel, when the slope is higher this makes v_f higher which will result in a higher vAve. Also if the slope is lower, v_f will be less resulting in vAve being less.
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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):
Don’t remember the exact formula for potential energy, however as height increase potential energy increases resulting in more energy to push the ball down the ramp.
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How might you verify whether your speculations are indeed valid explanations?
Your answer (start in the next line):
Find the potential energy formula and calculate.
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Do your data conclusively show that the disk made a difference?
Your answer (start in the next line):
Three domino ave ‘dt= approx 1.141s
Three domino with CD ave ‘dt= approx 1.511s
Three domino with paper ave ‘dt = approx 1.149s
It seems as though the disk made a difference of a little over .3s. Yes it 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):
It seems as though the paper did not make a difference with a difference a approx .008s. The timing is not accurate to that level.
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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 be unable to tell the difference at about 1/3 the thickness of the DVD.
The difference between the DVD and non DVD time was approx .3s. The timer program is only accurate to about .1s. .1s/.3s = 1/3
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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 less because the difference in heights was less.
I think I would be able to detect a thinner object better using the one domino set up. The difference in height is less and the paper would be a higher percent of the smaller difference in height.
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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 balls velocity changes more quickly with the 3 domino set up. Since we know v_0, ‘dt, ‘ds we can calculate.
vAve=’ds/’dt
v_f=2*vAve
‘dv=v_f-v_0
aAve=’dv/’dt
Using the above we can calculate aAve for all three 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):
One and a half hours.
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*#&!
&#Your work on this lab exercise looks very good. Let me know if you have any questions. &#