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course phy 202
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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It gets shorter by, I would estimate, about 10%.
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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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The volume decreases. The volume is proportional to the length, so I would say that it also decreases by about 10%.
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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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The number of molecules remains the same, so there is a 0% change.
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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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The mass is related to the number of molecules, so the mass remains constant as well, or there is a 0% 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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The pressure in the air column increases. The ratio of the volume change is equal to the ratio of pressure change, so I would estimate that the pressure also increases by 10%.
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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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The pressure in the bottle increases. The bottle and the tube are connected, so the change in pressure in each would be the same, thus, the pressure increases by about 10%.
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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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I think the forces would be equal. If the sum of the forces between the two was anything other than zero, there would be some form of acceleration, or the water plug would be moving. Since the water is stationary, the sum of the forces must be zero. This means that they are equal and opposite.
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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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I think the pressure in the bottle and the pressure in the air column are equal. The water moves along in the tube until the pressure on one side is equal to the pressure on the other side.
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Measure the length of the air column.
What is the length of the air column?
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17.2 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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1.72 cm or it would have to be a length of 15.48 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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About 7 or 8. I was able to go further than 10% if I needed to, but it took a pretty hard squeeze to get it that far.
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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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A 2 moved it to a length of 16.8, or about 3.5% of its original length. A 5 moved it to a length of about 16 cm, or 7% of the original length. An 8 moved it to about 15.2 cm or about 12% of its original length.
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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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I ran the bottle under some hot water, and watched the length of the air column decrease. I then ran the bottle under some cold water, and the length of the air column increased.
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Brief Bottle Experiment 1c
Siphoning water into empty sealed bottle
Starting with the cap in place on an empty bottle, siphon water from an adjacent full bottle. Allow the siphon to run a few minutes until the water levels in the two bottles stabilize.
Estimate the percent change in the volume of the air in the capped bottle.
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About 20%.
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Estimate the percent change in the number of molecules in the air within the capped bottle.
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0% (No air molecules could have escaped)
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Estimate the percent change in the volume of the water in the open bottle.
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About 50%.
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What do you think is the percent change in the air pressure in the capped bottle?
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If the volume changes by about 20%, then the pressure must also change by about 20%
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What is the difference in the two fluid levels?
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The two levels are equal.
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What is the percent change in the number of air molecules in the capped bottle?
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0%. The air could not have changed
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Raise the open bottle as high as possible without disturbing the capped bottle. Allow time for the water levels in the two bottles to stabilize.
What percent of the volume of the capped bottle do you now estimate is occupied by water?
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About 50%. Water flowed from the open bottle into the capped bottle.
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Estimate the percent change in the number of molecules in the air within the capped bottle.
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0% No air could escape from the capped bottle.
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By what percent do you estimate the pressure in the capped bottle exceeds the original pressure (i.e., the pressure when the bottle was first capped)?
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About 50% (I squeezed the bottle initially so that the pressure was able to increase by a significant amount).
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What percent of the uncapped bottle do you estimate is now occupied by air?
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I did not fill it all the way. I’d say it is about 30% full now, so about 70% is occupied by air.
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What is the difference in the two water levels?
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The water level of the open bottle is now lower than the water level of the closed bottle as long as the open bottle is raised.
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Return the uncapped bottle to the tabletop. What happens?
What is now the difference in the two water levels?
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Water goes from the capped bottle into the open bottle until the water levels are the same height once again.
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What do you think is the pressure in the uncapped bottle as a percent of its original pressure (before the bottle was capped)?
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I’d say that the water would fill up the capped bottle until the pressure was equal to the pressure outside. Since I tampered with it a little, I’m not exactly sure what the answer would be.
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Brief Bottle Experiment 1d
Raising water
Add the extension to the tube, so that by squeezing you can force water from the bottle into the tube. Squeeze hard enough to raise the water to as high as possible into the tube. Evaluate how hard you had to squeeze, on the 1-10 scale you used in part 1b. Measure how far you were able to raise water in the tube above the level of the water in the bottle.
How high did you raise the water, and how hard did you have to squeeze (using the 1-10 scale)?
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If I hold the tube straight up in the air, it take about 7 to get it the water close to the top, and about a 9 to get the water to actually come out of the tube.
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Give the bottle a squeeze corresponding to 1 on the 1-10 scale, and observe how high water rises. Then give it another squeeze, halfway between 1 and the squeeze you used to raise water to the top of the tube. Do this blind. Don't look at the tube, just feel the squeeze. Then look at the tube and see where the water is.
Report a table of water column height vs. squeeze.
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30 cm, 6
18 cm, 3
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&#Good work. Let me know if you have questions. &#