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course PHY 232
6/28 6:45
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?
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decreases, air escapes due to squeezing.
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Does the volume of air enclosed in the bottle increase or decrease?
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Decreases, because I squeeze out air.
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Does the pressure in the bottle increase or decrease?
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Same, pressure isn’t affected because air is allowed to escape
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Does the temperature of the air in the bottle increase or decrease?
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same, squeezing doesn’t change temperature.
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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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Stays the same, because air cannot escape.
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Does the volume of air enclosed in the system increase or decrease?
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Decreases because by squeezing the molecules come close to eachother.
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Does the pressure in the system increase or decrease?
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Pressure increases because molecules are closer.
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Does the temperature of the air in the system increase or decrease?
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same, because pressure and volume are opposite in PV=nRT.
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Brief Bottle Experiment 1b
The Air Column as a measure of 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?
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It gets shorter by 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 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 the pressure also increases by 10%.
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There is no ratio of volume change or of pressure change. There is only one volume change and one pressure change, so neither constitutes a ratio.
There is a ratio of volumes and a ratio of pressures, and they are related, but they aren't equal. These two ratios are reciprocals of one another.
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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. The sum is 0 so equal.
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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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17.1 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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1.71 cm or it would have to be a length of 15.49 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% but it was difficult.
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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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At 2 moved it to a length of 16.8, or about 3.5% of its original length. At 5 moved it to a length of about 16 cm, or 7% of the original length. And at 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
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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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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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2% because air bubbles of tube.
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Estimate the percent change in the volume of the water in the open bottle.
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10%
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What do you think is the percent change in the air pressure in the capped bottle?
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20%
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What is the difference in the two fluid levels?
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uncapped is twice as much water
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What is the percent change in the number of air molecules in the capped bottle?
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10%
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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 20-30%
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Estimate the percent change in the number of molecules in the air within the capped bottle.
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about 10-15 % increase
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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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5% with air bubbles
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What percent of the uncapped bottle do you estimate is now occupied by air?
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65%
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What is the difference in the two water levels?
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uncapped is like twice as much
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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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no change
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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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Less pressure because there isn’t as much water.
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Brief Bottle Experiment 1d
Raising water
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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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3, it only took a slight squeeze to raise the water to the extension piece.
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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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Squeeze: 1, 2
Water column height: 1 cm, 7 cm
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Good, but be sure to check my notes.
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