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course Phy 122
Jan. 1711:30 AM
Brief Bottle Experiment 1A: Basic concepts of N, P, V, T
It 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, the air is pushed out
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Does the volume of air enclosed in the bottle increase or decrease?
**** Decrease, the air is pushed out
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Does the pressure in the bottle increase or decrease?
**** Decrease, air comes out so pressure decreases
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If the bottle remains open to the air outside, the pressure within the bottle will remain equal or very close to the pressure outside. If there is a difference in pressure air will move quickly from the region of greater to the region of lesser pressure. This of course happens during the squeeze, but it's over after the squeeze has occurred.
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Does the temperature of the air in the bottle increase or decrease?
**** Decrease, less pressure equals lower temperature
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In a closed container at constant volume the only way to decrease pressure would be to cool the gas. However the container isn't closed, so evern if the pressure decreases you can't make this inference.
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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?
**** Neither, no air goes in or out
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Does the volume of air enclosed in the system increase or decrease?
****Decrease, the air is compacted
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Does the pressure in the system increase or decrease?
**** Increase, nothing comes out so pressure is not relieved
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Does the temperature of the air in the system increase or decrease?
**** Increase, more pressure equals higher temperature
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The increase in pressure is the result of the decrease in volume, not an increase in temperature.
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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?
**** Slightly shorter, 5%, the air becomes more compact but it doesn’t shorten the length much
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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?
**** Decrease, the air is compacted, 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?
**** Remain the same, 0%, no air goes in or out
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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?
**** Remain the same, 0%, no air goes in or out
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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?
**** Increase, 20%, nothing comes out so pressure is not relieved
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As we will see, assuming constant temperature in the tube, the air pressure is inversely proportional to the volume, which in turn is proportional to the length of the tube.
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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?
**** Increase, 10%, nothing comes out so pressure is not relieved
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The pressure in the bottle is the same as in the tube. If it wasn't the water 'plug' would accelerate in the direction of lower pressure.
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This does in fact occur when the bottle is squeezed; the water plug ends up moving toward the end of the tube. However when the squeeze is finished, there is no additional motion of the water plug.
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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?
**** Pressure in the bottle, the water plug moves more toward the capped end
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Which do you think is greater, the pressure in the bottle or the pressure in the air column?
**** Air column, it won’t compress any more but the bottle will
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Measure the length of the air column.
What is the length of the air column?
**** 19 cm
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How far would the water plug have to move to make the air column 10% shorter?
**** 1.9 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?
**** 8, 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?
**** 2-2%
**** 5-6%
**** 8-10%
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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:
**** 18 cm
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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.
**** 53%, almost half of the water was siphoned out
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Estimate the percent change in the number of molecules in the air within the capped bottle.
**** 47%, almost half of the water was replaced by air
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Estimate the percent change in the volume of the water in the open bottle.
****47%, almost half of the water was siphoned in
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What do you think is the percent change in the air pressure in the capped bottle?
**** 47%, less water less pressure
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What is the difference in the two fluid levels?
**** Capped bottle is slightly more, not all water was siphoned out
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What is the percent change in the number of air molecules in the capped bottle?
**** 47%, almost half of the water was replaced by air
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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?
**** 99%, hardly any water was siphoned out
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Estimate the percent change in the number of molecules in the air within the capped bottle.
**** 1%, hardly any air came in
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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)?
**** 1%, hardly any pressure was relieved
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What percent of the uncapped bottle do you estimate is now occupied by air?
**** 99%, hardly any water was siphoned in
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What is the difference in the two water levels?
**** Capped bottle hardly lost any water
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Return the uncapped bottle to the tabletop. What happens?
What is now the difference in the two water levels?
**** Water levels have not changed, the siphon did not start when the uncapped bottle returned to the table
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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)?
**** 100%, pressure did not change
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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)?
**** 70.9 cm, 4
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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.
**** 10.1 cm
**** 38.9 cm
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In part C, as we saw in class, very little water ends up in the capped bottle.
I've inserted some notes related to parts A and B. Your observations were good overall but a couple of points needed to be clarified.
Part D looks good.
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