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course Phy 232
6/17 11:25PM
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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The amount of air in the bottle will decrease because it will exit through the tube opening.
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Does the volume of air enclosed in the bottle increase or decrease?
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The volume of enclosed air in the bottle also decreases because when the bottle is squeezed, it stays in that form is less room for air inside the bottle after.
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Does the pressure in the bottle increase or decrease?
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The pressure in the system will remain the same. The open end causes air to continuously flow in and out of the bottle causing the pressure to neither build up nor drain out.
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Does the temperature of the air in the bottle increase or decrease?
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The temperature of the air inside of the bottle must decrease. The volume decreases inside the bottle, temperature, and volume are directly proportional.
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The number of molecules in the bottle doesn't remain constant. So you can't conclude a proportionality between temperature and volume.
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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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The amount of air in the system remains the same because the air has nowhere to leave the system.
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Does the volume of air enclosed in the system increase or decrease?
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The volume remains constant in the system. The bottle cannot be compressed and the air in the system has nowhere to escape to allow the bottle to be squeezed and remain crushed down.
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The volume of the air decreases. You compress the bottle, reducing the volume inside.
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Does the pressure in the system increase or decrease?
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If the bottle is squeezed with the cap on the pressure in the system will increase.
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Does the temperature of the air in the system increase or decrease?
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The temperature in the system increases because the pressure in the system increases and in this case temperature and pressure are directly proportional.
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It's good that you're thinking about the proportinonalities. However the volume does not remain constant so this proportionality will not occur.
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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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After squeezing the bottle, the air column gets shorter by a little. The percent change is approximately 5%-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 of the air column decreases because the liquid takes up some of the space previously occupied by the air column. When there is less space, there is less volume.
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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 in the air column remains the same because at the end of the tube, a cap is placed to prevent air leakage. When there is less space, the air just gets closer together but the total molecules remain the same because there is nowhere else for the air to go.
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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 of the air also remains the same as the total weight. No air is lost or gained by squeezing the bottle because there is no place for the air to be released and no new air is added into the system. The mass of the air as a whole is constant. However the mass of the air per unit of distance does increase because the same amount of air at the beginning must fit into a smaller region.
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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 because the volume decreases, which causes there to be less room for the same amount of air that initially took up more space before the air column shortened.
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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 remains the same because the pressure created by squeezing the bottle is transferred into the air column. This caused the bottle to remain at the same pressure as it started.
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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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The greater force is the one pushing towards the capped end. This is because the pressure generated by squeezing the bottle moves down the tube towards the capped end. The air column gets shorter and also builds up more pressure. The pressure from the bottle is greater than the pressure generated from the air column in the opposite direction causing the plug to move towards the capped end a little ways.
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If there was a difference in pressure then, since the areas of the ends are equal, there would be a nonzero net force on the water 'plug', which would therefore accelerate in the direction of the greater force.
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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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The pressure in the air column and the pressure in the bottle are equal. This is shown by the air column remaining at a constant length when the bottle is held down squeezed.
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Measure the length of the air column.
What is the length of the air column?
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9 1/4 inches.
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How far would the water plug have to move to make the air column 10% shorter?
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.925 inches
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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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An 8 on the hardest scale with a 10 % difference.
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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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2 - 2.7% changes in the length of the air column.
5 - 5.4% changes in the length of the air column.
8 - 10% changes in the length of the air column.
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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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Using the hot and cold water alternatives, the air column changes in length by +- .9 inches from the original recorded length.
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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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Around 25% change in the volume of the air in the capped bottle.
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Estimate the percent change in the number of molecules in the air within the capped bottle.
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0% because none of the molecules in the air.
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Estimate the percent change in the volume of the water in the open bottle.
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Around 50% change in the volume of the water in the open bottle.
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What do you think is the percent change in the air pressure in the capped bottle?
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Around 20% change in the air pressure in the capped bottle.
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What is the difference in the two fluid levels?
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Both levels are equal so there is no difference.
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What is the percent change in the number of air molecules in the capped bottle?
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0% because the air molecules don’t change during the process.
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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 50% of the volume of the capped bottle because the water flowed from the open bottle into the capped bottle.
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Estimate the percent change in the number of molecules in the air within the capped bottle.
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0% because no air could escape from the bottle with the cap.
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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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50% of the pressure in the capped bottle exceeds the original pressure because squeezing the bottle caused an increased pressure.
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What percent of the uncapped bottle do you estimate is now occupied by air?
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The bottle is about 25% full with water. This means 75% is taken up by air.
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What is the difference in the two water levels?
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The water level of the open bottle is lower than the water level in the closed bottle. This is because the open bottle is being raised up.
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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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Water now flows back into the capped bottle from the open bottle until the water levels are the same again.
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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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The water would continue to run into the capped bottle, filling it up until the pressure inside of the capped bottle is close to or equal to the pressure outside of the bottle. It is hard to estimate the exact percentage of pressure change though.
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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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It took about a squeeze of level 9 to get the water up to the top of the tube when the tube was held straight up in the air.
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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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1, around 5.2 inches
5, around 9.7 inches
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&#Good responses on this lab exercise. See my notes and let me know if you have questions.
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