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course Phy 202
These are the experiments we did from the first day of class I emailed to you and now are submitting through forum.
Experiment 1AScrew 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:
1. Does the amount of air in the bottle increase or decrease?
The amount of air in the bottle decreases because the container becomes smaller.
2. Does the volume of air enclosed in the bottle increase or decrease?
The volume probably also decreases because the container became smaller.
3. Does the pressure in the bottle increase or decrease?
The pressure in the bottle remains the same because the air is being forced out.
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The pressure remains the same because the bottle is open to the atmosphere throughout.
When the volume is decreased without changing the temperature, air must escape in order to keep the pressure constant.
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4. Does the temperature of the air in the bottle increase or decrease?
The temperature in the bottle will remain the same because pressure hasn’t
increased.
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:
5. Does the amount of air in the system increase or decrease?
In the system, the amount of air stays the same because no air was allowed to
escape.
6. Does the volume of air enclosed in the system increase or decrease?
The volume of the air in the system stays the same because no air escaped.
7. Does the pressure in the system increase or decrease?
The pressure of the system increased because the bottle (container) becomes
smaller.
8. Does the temperature of the air in the system increase or decrease?
The temperature of the system increases because the container is smaller, causing
the molecules of air to collide more often which releases more heat.
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More frequent collisions do not by themselves increase the temperature. The kinetic energies of the particles must increase in order to increase temperature.
In fact, there is an increase in temperature, since every collision of a particle with the approaching sides of the bottle speed it up.
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Experiment 1B
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.
1. 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. I would estimate it got shorter by about 10%.
2. 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 because the water plug is pushing against
it. I would estimate about 10-15%.
3. 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 in the air column would remain the same.
4. 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 does not increase of decrease because you are not adding or subtracting
molecules by compressing the air column.
5. 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?
The pressure in the air column would increase because the volume decreases. I
would estimate about 10-15%.
6. Does the pressure in the bottle increase, decrease or remain the same? By what percent do you conjecture the pressure in the bottle changes?
The pressure in the bottle would remain the same because the pressure is being
pushed out of the bottle.
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Pressure isn't the sort of thing that can be moved around.
The pressure in the bottle and the pressure in the air column equalize, becoming equal when the 'water plug' in the tube becomes stationary.
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7. 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?
Because it is stationary, the two forces would be equal.
8. Which do you think is greater, the pressure in the bottle or the pressure in the air column?
The pressure in the air column and bottle would be the same.
Measure the length of the air column.
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Right. Be sure you see the inconsistency between this and your earlier answer.
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9. What is the length of the air column?
The air column was about 7.5 cm.
10. How far would the water plug have to move to make the air column 10% shorter?
It would have to move 0.75 cm, or just under 1 cm to make it 10% shorter.
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.
11. 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?
10% change. I squeezed as hard as a 5.
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.
12. What were your percent changes in air column length?
2 = about 5%, 5 = about 10%, 8 = about 15%
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:
I heated the bottle with a blow dryer and the air column subtly got smaller. Immediately afterwards, I wrapped an ice pack around the bottle and due to the colder temperature of the air in the bottle, the pressure in the tube decreased and the air column expanded some. I took my thumb off the end of the tube prematurely and the remaining extra pressure from the heat caused the water to shoot out.
Experiment 1C
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.
1. Estimate the percent change in the volume of the air in the capped bottle.
It changed (reduced) by about 50%.
2. Estimate the percent change in the number of molecules in the air within the capped bottle.
The number of molecules have decreased by about half because there is half as
much air.
3. Estimate the percent change in the volume of the water in the open bottle.
The water has decreased by about half.
4. What do you think is the percent change in the air pressure in the capped bottle?
The air pressure wouldn’t have changed because I have to leave the bottle open to
allow it to siphon.
5. What is the difference in the two fluid levels?
The two fluid levels are equal.
6. What is the percent change in the number of air molecules in the capped bottle?
The air molecules have probably decreased by about half.
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.
7. What percent of the volume of the capped bottle do you now estimate is occupied by water?
Almost all of the volume is occupied by water.
8. Estimate the percent change in the number of molecules in the air within the capped bottle.
The air molecules have been reduced to almost none. So maybe 90-100%.
9. 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)?
The air pressure shouldn’t matter now that its filled with water.
10. What percent of the uncapped bottle do you estimate is now occupied by air?
About 100%.
11. What is the difference in the two water levels?
Significant. They don’t match now. One is full, one is empty.
12. Return the uncapped bottle to the tabletop. What happens?
The water levels now match up.
13. What is now the difference in the two water levels?
They are equal again.
14. What do you think is the pressure in the uncapped bottle as a percent of its original pressure (before the bottle was capped)?
The pressure is the same as atmospheric pressure because my bottle is open in
order to siphon.
Experiment 1D
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.
1. How high did you raise the water, and how hard did you have to squeeze (using the 1-10 scale)?
I put about 5 cm of water into the bottle and squeezed as hard as about a 7 to try
to get the water close to the top of the tube without squeezing it out. I measured
that I squeezed it up about 80 cm.
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.
2. Report a table of water column height vs. squeeze.
1 = about 8 cm, 4 = about 25 cm, 7 = about 80 cm
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Thanks for submitting this.
Check the notes I've inserted.
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