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course PHY 231
10/09/10 10:48 am. Part of this I couldn't do since I wasn't there that day. If/when we do that part, magnet/balance, again I'll finish it.
The Atwood system consists of the paperclips suspended over the pulley. A total of six large clips connected by a thread were suspended, three from each side of the pulley. The system was released and, one side being slightly more massive than the other due to inconsistencies in the masses of the clips, accelerated from rest, with one side descending and the other ascending. The system accelerated through 50 cm in a time interval between 4 and 6 seconds; everyone used their 8-count to more accurately estimate the interval. Then a small clip was attached to the side that had previously ascended. This side now descended and the system was observed to now descend is an interval that probably lasted between 1 and 2 seconds.If you weren't in class you can assume time intervals of 5 seconds and 1.5 seconds. Alternatively you can wait until tomorrow and observe the system yourself; the initial observation requires only a couple of minutes.
`qx001. What were your counts for the 50 cm descent of the Atwood system?
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I missed this and when we looked at it again I wasn't able to get a good count so I'm using the given values above.
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`qx002. What were the two accelerations?
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4, 44.4
This is in cm/s^2 and are for the 5 s and 1.5 s intervals respectively.
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`qx003. Why did the systems accelerate?
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Gravity was accelerating them when they were released.
Gravity was pulling on both sides, pulling the system in opposite directions. Under what conditions would that reult in a nonzero acceleration?
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`qx004. Suppose the large paperclips all had mass 10 grams, the small clip a mass of 1 gram. What then was the net force accelerating the system on the first trial, and what was the net force on the second?
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40, 448
This is uncertain to me about the mass of the large clips, is it saying they all had 10 g total or each? Each seems to be way too much so I'm assuming 10 total. I'm This is in g*cm/s^2 and is for the 5 and 1.5 intervals respectively.
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.. if uncertainty +-1%
`qx005. Given the masses assumed in the preceding, what is the force acting on each side of the system? What therefore is the net force on the system?
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For the 3/3 system the force on each side should be 29.4 cN but this isn't so because the system moved so there has to be some inequality. For the 3/4 system one side would be 29.4 cN and the other 39.2 cN. Here cN is centi-Newtons. So the first should have a F_net of 0, but clearly does not, and the second system should be 9.81 cN.
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`qx006. Based on your counts and the resulting accelerations, do you think the ratio of the masses of the large to small paperclips is greater than, or less than, the 10-to-1 ratio assumed in the preceding two questions?
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It seems pretty close, especially looking at the last result for the 3/4 system since it had one cN more force, which should be expected for adding one gram to that side since 1g---> 9.81 cN.
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`qx007. If the mass of each larger clip is M and the mass of a smaller clip is m, what would be the expressions for the net force accelerating the system? What would be the expression for the acceleration of the system?
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F_net = 3Mg-(3M+m)g= mg. I think I'm missing something here as the F_net probably shouldn't be mg since the system was not accelerating at the rate of g.
Right. F_net = mass * acceleration; all the mass of the system is being accelerated so F_net would be (M + m) * a, where a is the acceleration of the system.
Therefore
3 M g - (3 M + m) g = (M + m) * a.
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`qx008. If the mass of the each of the larger clips is considered accurate to within +-1%:, would this be sufficient to explain the acceleration observed when 3 large clips were hung from each side?
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Seems that the ratio should be larger than this since the ratio of the accelerations is 44:4 and 4 is 9% of 44.
you should instead be comparing the acceleration of the system with three large clips on each side, to the acceleration of gravity
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... sample the accelerations for random divisions of the six large clips ... predict what the distribution of masses would look like ...
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I didn't get a lot of time to look at the Atwood system and am not certain about these answers but I have tried to apply what I understood about the lecture on this since I was there for that. Also, I missed the experiment below and it doesn't seem that we've revisited yet but if/when we do I'll come back and finish this.
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Magnet and Balance
Everyone was given a small magnet and asked to achieve a state where the balance was in an equilibrium position significantly different from that observed without the magnet. It was suggested that the length of the suspended clip beneath the surface of the water should differ by at least a centimeter.
... assuming 1 mm diam ...
`qx009. Describe in a few lines your efforts to achieve the desired result. What worked, what didn't, what difficulties presented themselves, etc.?
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`qx010. How much difference was there in the length of clip suspended in the water? If you didn't actually measure this, give a reasonable estimate.
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`qx011. How did you adjust the magnet? If you wanted to quickly increase or decrease the length of the suspended paper clip beneath the surface by 1 millimeter, using only what you had in front of you during the experiment, how would you go about it?
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`qx012. Assuming the diameter of the suspended clip to be 1 millimeter, by how much did the buoyant force on the suspended clip change? How much force do you therefore infer the magnet exerted? If you have accurate measurements, then use them. Otherwise use estimates of the positions of various components as a basis for your responses.
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I'm likely to have you take the buoyant balances home, so you should get a chance to try this last one out.
See my notes on the earlier questions.
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