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course Phy 202
2/19 11 pm
Brief Bottle Experiment 1bThe Air Column as a measure of Pressure
Siphon a plug of water into the tube, seal the end of the tube to create an air column between the plug and the sealed end, and screw the cap back on. Give the bottle a moderate squeeze. Note that the tube should have come with a cap on the end, but the cap might have been left off; if so you can seal the end with your thumb; if the end is cut at a sharp angle you can easily cut it off square.
Does the air column get longer or shorter? By what percent do you estimate the length of the column changes?
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shorter by about 5%
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Does the volume of the air column increase or decrease? By what percent do you estimate the volume of the column changes?
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decrease by about 5%
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Does the number of molecules in the air column increase, decrease or remain the same? By what percent do you estimate the number of molecules changes?
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remain the same
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Does the mass of the air in the air column increase or decrease? By what percent do you estimate the mass of the air in the column changes?
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increase by 5%
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If no air gets in or out the mass of the air in the column doesn't change.
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Does the pressure in the air column increase, decrease or remain the same? By what percent do you conjecture the pressure in the column changes?
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increase by 5%
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Does the pressure in the bottle increase, decrease or remain the same? By what percent do you conjecture the pressure in the bottle changes?
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increase by 5%
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When you hold the bottle in the squeezed position, with the water plug stationary, the pressure in the bottle results in a force on the plug which pushes it toward the capped end, while the pressure in the air column results in a force that pushes the plug away from that end. Which force do you think is the greater, or are they equal?
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air column
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If you hold the bottle in the squeezed position the water column remains stationary. If the water column doesn't accelerated, the net force on it is zero. So the forces on the ends are equal and opposite (not quite so if the water is higher on one side than on the other, in which case the excess weight of water on one side implies a slightly smaller force from the pressure; however the pressure forces will be much greater than the weight of the water so this won't make a lot of difference).
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Which do you think is greater, the pressure in the bottle or the pressure in the air column?
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air column
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Discounting the relatively insignificant effect due to the weight of the water, the equality of the forces on the two ends of the 'water plug', along with the uniformity of the tube, imply that the pressures are equal.
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Measure the length of the air column.
What is the length of the air column?
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20.4 cm
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How far would the water plug have to move to make the air column 10% shorter?
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2.04 cm
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Squeeze the bottle so the air column becomes 10% shorter. It's up to you to figure out how to tell when it's 10% shorter. If you can't squeeze hard enough to achieve the 10% difference, then figure out what percent you can manage and note the percent in your answer.
On a 1-10 scale, with 10 the hardest squeeze of which you are capable without risking injury, how hard did you have to squeeze the bottle and what percent change did you achieve in the length of the air column?
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10, 21% change because the air column measured at 16.1 cm
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Now, using the same 1-10 scale, give the bottle squeezes of 2, 5 and 8. Estimate the percent changes in the length of the air column.
What were your percent changes in air column length?
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.6%, 1.86%, 4.97%
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Now by heating and/or cooling the bottle, what extremes in air column length can you achieve? Careful not to melt the bottle. It won't handle boiling water, and you shouldn't mess with water hot enough to scald you or cold enough to injure you (e.g., don't use dry ice, which in any case is too cold for the bottle, and certainly don't use liquid nitrogen).
Report your results:
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when heated the air column length seemed to get shorter but it was not at an considerable amount, maybe because the water in the bottle didn't get to hot due to me using the microwave. I'm assuming if the water was hotter then the air column would have been shorter due to the water rising up through the tube from the temp. increase
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The point is to heat the air in the bottle. The microwave heats the water, not the air. The intent was that this be done using tap water run over the bottle. You should give that a try. It just takes a minute and you'll get a good feel for the results, compared to the results of your 'hard squeeze'.
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No need to report, but do take a minute and do it.
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end document
&#Good responses. See my notes and let me know if you have questions. &#