#$&*
course PHY 202
Brief Bottle Experiment 1A: Basic concepts of N, P, V, TIt is assumed that you have read through the file Physics_II_Initial_Bottlecap-and-tube_Experiments.htm, which will familiarize you with the bottlecap and tube and some of their uses.
The bottlecap can be screwed onto a typical soft-drink bottle. It probably won't work on a bottle which isn't designed for the higher pressure of a carbonated drink, such as a water bottle or some tea bottles. A larger bottle is preferable, but any size will work adequately. A clear bottle is preferable to a colored bottle since you're going to sometimes want to see what's happening inside the bottle, and a darkly colored bottle won't allow this.
Screw the bottlecap onto a bottle and squeeze the bottle. It should be no surprise that if the tube isn't capped, this will force air out of the tube.
Comparing the state of the bottle before and after you squeeze:
Does the amount of air in the bottle increase or decrease?
****Decrease
#$&*Pressure being placed on the bottle forces some of the air volume in the bottle to exit the bottle through the tube connected to it. Pressure and Volume are inversely proportional. Therefore, when we apply pressure to the bottle, the volume in it will decrease.
@& Pressure and volume are inversely proportional only for a confined gas. The tube being open, this gas is not confined, so in this situation pressure and volume are not inversely proportional.*@
Does the volume of air enclosed in the bottle increase or decrease?
****Decrease
#$&*The increase of pressure on the bottle causes some of the air volume to exit the bottle through the tube connected to it.
Does the pressure in the bottle increase or decrease?
****Increases until the force acting upon stops, squeezing.
#$&*The force of the squeeze increases the pressure in the bottle causing some of the air volume in the bottle to exit. When the squeeze stops adding a force on the system, the pressure and volume remain constant in the bottle.
@& It might be more accurate to say that the squeeze decreases the volume of the container itself, which with the tube being open causes gas to exit the bottle until pressure is again equal to that of the atmosphere.*@
Does the temperature of the air in the bottle increase or decrease?
****Stays the same
#$&* Temperature is not affected with an increase in pressure if the system is open. The air molecules are not put under enough stress.
@& Consistent with your intuition on the preceding questions, the pressure does increase when the bottle is first squeezed. However the air quickly exits and the pressure equalizes.
As you say, the temperature does not change substantially.*@
Be sure you have explained all your answers.
Now cap the end of the tube and give the bottle a good squeeze, without straining yourself.
Comparing the state of the bottle before and after you squeeze:
Does the amount of air in the system increase or decrease?
****Remains the same
#$&*There is no way for the air to escape when it is in a closed system.
Does the volume of air enclosed in the system increase or decrease?
****The volume in the closed system decreases.
#$&*The force being applied to the closed system causes the size of the bottle to decrease, therefore causing the volume inside of it to decrease as well.
Does the pressure in the system increase or decrease?
****Increase
#$&* The force being placed on the bottle from the experimenter squeezing it causes the pressure inside the bottle to increase as the volume inside decreases.
Does the temperature of the air in the system increase or decrease?
****Stays the same
#$&* The temperature remains the same. Temperature can be increased with pressure if the volume is condensed, however in this experiment it is not enough of a change if any to take into consideration.
Brief Bottle Experiment 1b
The Air Column as a measure of Pressure
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Siphon a plug of water into the tube, seal the end of the tube to create an air column between the plug and the sealed end, and screw the cap back on. Give the bottle a moderate squeeze.
Does the air column get longer or shorter? By what percent do you estimate the length of the column changes?
****The air column gets shorter by approximately 10%.
#$&*The increase in pressure in the system forces some of the air volume from the bottle into the tube, pushing the water in the tube closer to the end.
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 the air column decreases due to the air pressure being placed on it.
#$&*The air molecules in the column are becoming more condensed.
@& Good.
Formatting note: put your comments between the **** and the #$&*, but not on the same line as either.
For example this one should read:
****
The volume of the air column decreases due to the air pressure being placed on it.
The air molecules in the column are becoming more condensed.
#$&*
It's not a problem here, but on some submissions it would make a difference.*@
Does the number of molecules in the air column increase, decrease or remain the same? By what percent do you estimate the number of molecules changes?
****The number of molecules remains the same. 0% change.
#$&*The molecules can’t go anywhere, they are only being forced closer to one another.
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?
****The mass of the air column remains the same.
#$&*The molecules are forced closer together, but each one will still weigh the same.
Does the pressure in the air column increase, decrease or remain the same? By what percent do you conjecture the pressure in the column changes?
****Increase, about 10%
#$&*If the volume of the air column decreases by 10%, the pressure on it must increase by 10% because the two are inversely proportional.
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 by about 10%
#$&*When force is placed on the bottle, the amount of space inside the bottle for the air volume is decreased about 10%. Therefore, the pressure is increased about 10%.
When you hold the bottle in the squeezed position, with the water plug stationary, the pressure in the bottle results in a force on the plug which pushes it toward the capped end, while the pressure in the air column results in a force that pushes the plug away from that end. Which force do you think is the greater, or are they equal?
****I believe the two pressures are equal.
#$&*While the air column is shorter and has a smaller distance for the molecules to bounce back and forth from, it also has a much less number of molecules than the bottle and the air column behind the water. I believe the two equal each other out and the system has a continuous pressure throughout.
@& Good.
We know the pressures are equal because the water plug, which is pushed from one side by the pressure force in the bottle and from the other by the pressure force from the air column, remains stationary. (it's also important that the water plug have the same cross-sections on both ends)*@
Which do you think is greater, the pressure in the bottle or the pressure in the air column?
****I believe the two are equal and opposite.
#$&*This is why the water remains stationary in the tube.
Measure the length of the air column.
What is the length of the air column?
****approximately 30.5cm
#$&*
How far would the water plug have to move to make the air column 10% shorter?
****3.05cm
#$&*
Squeeze the bottle so the air column becomes 10% shorter. It's up to you to figure out how to tell when it's 10% shorter. If you can't squeeze hard enough to achieve the 10% difference, then figure out what percent you can manage and note the percent in your answer.
On a 1-10 scale, with 10 the hardest squeeze of which you are capable without risking injury, how hard did you have to squeeze the bottle and what percent change did you achieve in the length of the air column?
****On a scale of 1 to 10, I squeezed the system at a 7 to attain a 10% decrease in the size of my air column.
#$&*
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= about 2-3%, 5= about 8%, and 8= about 11%
#$&*
Now by heating and/or cooling the bottle, what extremes in air column length can you achieve? Careful not to melt the bottle. It won't handle boiling water, and you shouldn't mess with water hot enough to scald you or cold enough to injure you (e.g., don't use dry ice, which in any case is too cold for the bottle, and certainly don't use liquid nitrogen).
Report your results:
****When the temperature decreases, as in our experiment in class where we went outside, the air column became longer. When the temperature was increased, the air column became shorter.
#$&*This has to do with the air molecules in the air column. When the temperature is decreased, the molecules do not move a fast causing the pressure from the bottle to decrease. When the temperature is increased, the molecules move faster, causing the pressure from the bottle to be greater, therefore causing the air column to shorten.
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.
****The percent change in the capped bottle was approximately 50%. After starting the siphon, by squeezing the empty bottle, the water traveled from the full bottle through the tube into the empty bottle until each bottle contained 50% of the water.
#$&*
@& That shouldn't happen if the cap is tightly sealed. Take a couple of minutes and check it out.*@
Estimate the percent change in the number of molecules in the air within the capped bottle.
****The air still contains the same amount of molecules.
#$&*There is no way for these molecules to escape.
Estimate the percent change in the volume of the water in the open bottle.
****The open bottle lost 50% of its water to the closed bottle.
#$&*The pressure from the closed bottle caused by squeezing it pulled the water from the open bottle until the two were equal in the amount of water they contained.
What do you think is the percent change in the air pressure in the capped bottle?
****50% increase
#$&*Since the volume in the capped bottle decreased by 50%, the pressure in it must have increased by 50% since the two are inversely proportional.
What is the difference in the two fluid levels?
****The two fluid levels are the same.
#$&*The pressure from the closed bottle caused a force that pulled the water from the open bottle until the two water levels in both bottles were level with one another.
What is the percent change in the number of air molecules in the capped bottle?
**** 0%
#$&* The same amount of air molecules are in the capped bottle, they do however take up a smaller volume of space. The amount of air molecules in the open bottle has increased by 50% due to the fact that it lost 50% of its water volume to the capped bottle and air molecules were able to enter through the open top and fill the open space.
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?
****75%
#$&*The capped bottle pulled water in until the pressure that was placed on it by the squeeze was stabilized. Once the bottles sides were pushed back out to their normal positions, due the loss of pressure in the bottle, the capped bottle stopped pulling water from the open bottle.
Estimate the percent change in the number of molecules in the air within the capped bottle.
**** 0%
#$&* The molecules in the capped bottle are still the same, they have nowhere to go. The pressure on them is higher, so they are closer together.
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)?
****75% more pressure is in the capped bottle compared to when no water was in it.
#$&* Since the volume in the capped bottle decreased by 75%, the pressure in it increased by 75%.
What percent of the uncapped bottle do you estimate is now occupied by air?
****75% of the uncapped bottle is now occupied by air.
#$&* Only 25% of its original amount of water is left, so the remaining 75% of it is now occupied by air since air was able to enter the bottle through the open cap.
What is the difference in the two water levels?
**** 75% of water is in the capped bottle, 25% of water is in the uncapped.
#$&* This is due to the pressure from the capped bottle pulling water from the uncapped bottle until it returned to its normal pressure.
Return the uncapped bottle to the tabletop. What happens?
What is now the difference in the two water levels?
****They are still the same.
#$&*The open bottle doesn’t have enough pressure to pull its lost water back from the capped bottle. Its pressure is much less than the capped bottles, so it can’t take water away.
What do you think is the pressure in the uncapped bottle as a percent of its original pressure (before the bottle was capped)?
**** 0% pressure change in uncapped bottle.
#$&* The bottle was always open, so the air pressure was unable to change.
Brief Bottle Experiment 1d
Raising water
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Add the extension to the tube, so that by squeezing you can force water from the bottle into the tube. Squeeze hard enough to raise the water to as high as possible into the tube. Evaluate how hard you had to squeeze, on the 1-10 scale you used in part 1b. Measure how far you were able to raise water in the tube above the level of the water in the bottle.
How high did you raise the water, and how hard did you have to squeeze (using the 1-10 scale)?
****I raised the water until it was a couple cm from the very end of the tube and squeezed at about a 4 to get it there. I didn’t have to squeeze much at all.
#$&*
@& Good, but you don't mention how high the end of the tube was. It will be important to know how much higher the water in the tube is than the water in the bottle.*@
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.
****The second squeeze applying half as much pressure as it took to get the water to the top of the tube raised the water ¾ of the way to the top of the tube.
#$&*Tube outside of bottle is approximately 61cm.
@& I figured you would get around to mentioning that height.
Good.*@
*#&!*#&!
@& Good work.
Now take a few minutes to answer the questions below, and submit a copy of those questions with your answers.
The main goal here is to associate what you have seen with the standard symbols for these quantities, and begin to think in terms of these symbols.
N stands for the number of air molecules in the bottle.
n stands for the number of moles of air in the bottle.
There are N_A = 6.02 * 10^23 particles in a mole, so N = n * N_A.
V stands for the volume of the gas.
T stands for its temperature.
P stands for the pressure within the bottle.
Answer the following:
If the sealed bottle is squeezed with the tube uncapped:
Which of the quantities P, V, N, n, T increase?
****
#$&*
Which of the quantities P, V, N, n, T decrease?
****
#$&*
Which of the quantities P, V, N, n, T remain unchanged?
****
#$&*
List the quantites that change, and give a rough estimate of the percent change in each when you squeezed. A positive percent means the quantity increased, a negative percent means the quantity decreaseed.
****
#$&*
If the sealed bottle is squeezed with the tube capped:
Which of the quantities P, V, N, n, T increase?
****
#$&*
Which of the quantities P, V, N, n, T decrease?
****
#$&*
Which of the quantities P, V, N, n, T remain unchanged?
****
List the quantites that change, and give a rough estimate of the percent change in each when you squeezed. A positive percent means the quantity increased, a negative percent means the quantity decreaseed.
****
#$&*
If the temperature of the gas remains constant, the average speed of the molecules bouncing around inside the bottle also remains constant.
If this is the case, and the volume decreases, do the individual molecules strike the walls of the container harder, do they strike more frequently, or both? Explain
*****@