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Phy 122
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** Question Form_labelMessages **
Question 6
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The answers below are from the questions you posed to me from the experiment raising atmospheric pressure I.
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How much additional pressure does it take to support a column of water 52 cm high?
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P = rho g y = 1000 kg / m^3 *9.8 m/sec^2 * 0.52 m = 5096 N/M^2 = 5096 Pascals.
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This can be answered most simply with the relationships of Introductory Problem Set 5, Problem 1. It can also be answered using Bernoulli's equation.
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By what percent did the length of the air column change when you squeezed the bottle?
25%
Can you use the answers to these two questions to estimate atmospheric pressure?
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Atmospheric pressure I guess would be similar to the 0.25 * 5096 = 1274 Pascals
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The pressure in the air column was originally atmospheric pressure. The pressure then changed by around 25%.
So the change in pressure would have been around 25% of atmospheric pressure.
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Atmospheric pressure is greater than 25% of atmospheric pressure.
So if 25% of atmospheric pressure it 5000 Pascals, then atmospheric pressure must be greater than 5000 Pascals, not less.
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You need answers to both of the preceding questions to answer this question. Check my notes on the first question.
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See if my notes help. Either way, please submit another question form with either answers or additional questions.
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See my note indicating why your results indicate that 25% of atmospheric pressure is about 5000 Pa.
Then see if you can revise your conclusion.
Your result will be less than accepted atmospheric pressure because the length of a confined air column will not change by 25% in response to the pressure increase required to raise water 50 cm. Most likely the air column wasn't completely confined, indicating perhaps a small leak in the capped end.
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Send me a revision of that one result, and/or additional questions. It should take you only a few minutes to complete this one minor revision (or if necessary to ask a question).
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