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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.
** Ball Down Ramp_labelMessages **
6/19 at 4:47 PM
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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):
Time required to roll the length of the ramp will be least for the steepest ramp. The ball should travel with greater velocity, meaning faster, as the incline of the ramp increases.
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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):
From the least to the greatest, the time interval observed should decrease. I think I have correctly described the behaviors of numbers in the table because they should have an inverse relationship with one another.
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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):
1.703
1.906
1.982
1.876
1.826
1.061
1.762
1.073
1.687
1.625
Seems the ball took less time overall to get to the bottom of the ramp during the last trial, meaning it rolls better in the library from right to left than it does left to right. Could also have something to do with the table, the ball rolled off the table on the left side when I laid it down. So the incline might actually be more to this side due to an un-level table. I thought that the energy from the ball striking the bracket might make the pendulum move, but it didn’t.
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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):
1.250
1.178
1.250
1.312
1.281
1.375
1.328
1.359
1.296
1.453
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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):
1.093
1.125
1.109
1.140
1.140
1.062
1.062
1.063
1.062
1.093
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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):
.984
.936
.969
.938
.969
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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):
.951
.971
.969
.938
.953
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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):
These results support the hypothesis I stated in the first two questions. As the slopes got steeper, the time to cover the distance got shorter, meaning the ball was moving at a faster speed.
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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):
Average velocity = distance / time
The slope of the ramp is not directly related to average velocity, but as the slope gets steeper, the time interval gets shorter, which would increase the 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):
Gravity could cause the average velocity on these ramps to change with slope. The slope changing simply allows the ball to roll faster because gravity is acting on it. The fasted the ball could move would be in a vertical position, where it falls, and the only force acting on it then is in fact gravity.
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How might you verify whether your speculations are indeed valid explanations?
Your answer (start in the next line):
To verify, I can calculate the average velocity the ball rolled for each of the different slopes I used.
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Do your data conclusively show that the disk made a difference?
Your answer (start in the next line):
In some instances the disk made enough of a difference to be noticeable, but because it was a small change of slope, some of my time intervals without the disk are the same or greater than those with the disk.
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Do your data conclusively show that the piece of paper made a difference?
Your answer (start in the next line):
My data does not show conclusively that the piece of paper made a difference, because it was such a small change in slope the time intervals seem pretty much the same as from previous tests.
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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):
3/4 the thickness
I would guess that an object 3/4 the thickness of the CD would not make enough of a difference in the slope to be noticeable on the timer program based on experimental results.
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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):
With this setup, I would think that the times would be less than this setup without the CD. I would be better able to distinguish the presence of the thinner object using the 1 domino setup. One reason for this is that with the smaller slope, the ball will roll slower, which will make it easier to time.
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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 with the 2 domino setup changes faster than the ball’s velocity with the 1 domino setup. In both setups, the ball covers the same distance, but it covers the distance faster with the 3 domino system. Furthermore, the average velocity would have to be faster with the 3 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 hour
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&#Good responses. Let me know if you have questions. &#
• If you were to estimate a length for a given force using one of your graphs, what do you think would be the uncertainty in that length (e.g., +- .05 cm, or +- .13 cm, etc.) and what is your evidence for this estimate?
Your answer (start in the next line):
Uncertainty in my graph for an estimation of a length for a given force would be .25 cm. My evidence for this based off of information from my graph.
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&#Very good data and responses. Let me know if you have questions. &#