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course PHY 202
2/22 about 2 pm
The bottlecap can be screwed onto a typical soft-drink bottle. It probably won't work on a bottle which isn't designed for the higher pressure of a carbonated drink, such as a water bottle or some tea bottles. A larger bottle is preferable, but any size will work adequately. A clear bottle is preferable to a colored bottle since you're going to sometimes want to see what's happening inside the bottle, and a darkly colored bottle won't allow this.Screw the bottlecap onto a bottle and squeeze the bottle. It should be no surprise that if the tube isn't capped, this will force air out of the tube.
Comparing the state of the bottle before and after you squeeze:
Does the amount of air in the bottle increase or decrease?
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The amount of air decreases because it is forced out of the tube. Once the squeeze is let off, the air comes back inside the bottle.
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Does the volume of air enclosed in the bottle increase or decrease?
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The volume of the enclosed air in the bottle decreases because of the squeeze.
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Does the pressure in the bottle increase or decrease?
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It initially increases but then normalizes quickly.
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Does the temperature of the air in the bottle increase or decrease?
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Likely increases slightly due to body heat.
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Be sure you have explained all your answers.
Now cap the end of the tube and give the bottle a good squeeze, without straining yourself.
Comparing the state of the bottle before and after you squeeze:
Does the amount of air in the system increase or decrease?
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The amount of air stays the same because it is capped.
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Does the volume of air enclosed in the system increase or decrease?
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The volume of air decreases.
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Does the pressure in the system increase or decrease?
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Since the volume decreases, the pressure will increase. N, R, and T remain constant, so PV must remain constant. If V decreases, P must increase, so that P*V is still the same.
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Does the temperature of the air in the system increase or decrease?
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Again, minimal increase, but really remains constant.
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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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The air column gets shorter. It decreased by about 20%.
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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 also, by about 20%.
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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 because the end of the tube is capped.
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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 of the air column remains the same since no molecules escaped.
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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. Since n, R, and T are constant, if V decreases by 20 %, then P must increases by 25% to make P*V equal nRT.
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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 would increase the same amount as in the tube.
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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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They are equal if the plug is not moving.
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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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They are in equilbirum.
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Measure the length of the air column.
What is the length of the air column?
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16 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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1.6 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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3
10%
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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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2, 1.2 cm, 8%
5, 2.0 cm, 12.5%
8, 3.2 cm, 16%
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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 placed the bottle in front of a space heater for a few minutes. The air column decreased by about 2 cm, or about 12.5%.
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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 50%.
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Estimate the percent change in the number of molecules in the air within the capped bottle.
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No change.
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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 decrease by 50%, then the pressure increased by 200%, since nRT is constant. PV must also remain constant.
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What is the difference in the two fluid levels?
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They 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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No change.
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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 70%
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Estimate the percent change in the number of molecules in the air within the capped bottle.
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No change.
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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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If volume decreased by 70%, the pressure increased by 333%.
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What percent of the uncapped bottle do you estimate is now occupied by air?
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30%.
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What is the difference in the two water levels?
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They are not equal. There is more in the capped than in the uncapped.
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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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They are equal 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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The same because it is an open system, uncapped.
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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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5, 54 cm
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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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1 10 cm
3 30 cm
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&#This looks good. Let me know if you have any questions. &#