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course PHY 242
Brief Bottle Experiment 1A: Basic concepts of N, P, V, TIt is assumed that you have read through the file Physics_II_Initial_Bottlecap-and-tube_Experiments.htm, which will familiarize you with the bottlecap and tube and some of their uses.
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?
Decrease
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Does the volume of air enclosed in the bottle increase or decrease?
Decrease
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Does the pressure in the bottle increase or decrease?
Increase
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Does the temperature of the air in the bottle increase or decrease?
Increase
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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?
The amount of air stays the same since the end is capped.
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Does the volume of air enclosed in the system increase or decrease?
The volume of air in the system decreases since the bottle is being squeezed.
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Does the pressure in the system increase or decrease?
Since the volume is being decreased the pressure is increasing.
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Does the temperature of the air in the system increase or decrease?
I think the temperature increases since there is an added pressure.
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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?
The air column get shorter by about 25%.
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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?
The volume of air decreases by about 25%.
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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?
I think the number of molecules in the air column stays 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?
I think the mass of the air in the air column stays the same.
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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?
I think the pressure increases by the same amount that the volume decreased.
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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?
I think the pressure in the bottle increases by the same amount hat the pressure in the air column increased.
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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?
I think they are equal.
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Which do you think is greater, the pressure in the bottle or the pressure in the air column?
I think the pressure in the air column is greater since it is the same force but a smaller area.
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If the pressures are equal the force exerted on the sides of the air column is less than that exerted on the sides of the bottle, since the area of the sides of the air column is less than that of the bottle.
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Measure the length of the air column.
What is the length of the air column?
8 cm
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How far would the water plug have to move to make the air column 10% shorter?
0.8 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?
With a moderate to pretty hard squeeze I was able to get a 1 cm change or about 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?
.2, .5 and 1 cm respectively.
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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:
By holding the bottle over the stove I was able to get the air column to start increasing by fractions of a cm.
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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.
About 25%
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Estimate the percent change in the number of molecules in the air within the capped bottle.
I think the number of molecules stays the same.
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Estimate the percent change in the volume of the water in the open bottle.
There is about 50% change.
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What do you think is the percent change in the air pressure in the capped bottle?
I think this is about a 25% change
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What is the difference in the two fluid levels?
They are pretty even.
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What is the percent change in the number of air molecules in the capped bottle?
I think this number stays the same.
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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?
12%
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Estimate the percent change in the number of molecules in the air within the capped bottle.
I think the number of air molecules stays the same.
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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)?
I think by closer to 50%
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What percent of the uncapped bottle do you estimate is now occupied by air?
About 70%
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What is the difference in the two water levels?
The water level in the uncapped bottle is about 50% greater.
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Return the uncapped bottle to the tabletop. What happens?
What is now the difference in the two water levels?
The water levels start to even out.
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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)?
I think the pressure has returned to its original level.
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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)?
With a moderate squeeze the water level raised about 8 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.
10 cm 8
6cm 5
4 cm 4
2cm 2
0cm 0
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It's fairly easy to raise water half a meter in the open tube. You might get 8 cm if the vertical tube was closed at the top.
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