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course Phy 232
7/7 130pm
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 seems to decrease because the air can escape through the hole.
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Does the volume of air enclosed in the bottle increase or decrease?
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The volume of air seems to decrease because the bottle is being squezed which decrease the volume.
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Does the pressure in the bottle increase or decrease?
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The pressure seems to increase because the volume is decreasing.
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The amount of gas is also changing, so this might, but doesn't necessarily, follow.
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Does the temperature of the air in the bottle increase or decrease?
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The temperature doesnt seem to change because it is an open system.
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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 seems to remain constant since the tube is blocked off so no air can escape.
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Does the volume of air enclosed in the system increase or decrease?
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The volume of air decreases slightly as the bottle squeezes a little bit because the bottle loses volume.
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Does the pressure in the system increase or decrease?
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The pressure in the system increases because the volume is decreasing.
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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 seems to remain the same.
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The temperature does in fact increase, but not much and only for a short time, so the increase would not be detectable without a fast and sensitive thermometer.
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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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The air column gets shorter when the bottle is squeezed. It looks like it changes 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 of the air column decreases since the air column gets shorter. It 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 in the air column remain the same, because there is no where else for them 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 in the air column remains the same since the number of molecules remains about the same.
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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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Since the volume decreases, the pressure increases. This makes sense because there are more gas particles in a smaller amount of space. It changes by about 10 %.
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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 because the bottle still gets smaller, which makes the volume smaller. The pressure increases by 10-15 %.
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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 force of the pressure in the bottle is greater because it actually pushes the water plug towards the dealed end of the tube, and if the other pressure was greater it would go the other way.
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The plug ends up in equilibrium, indicating that all forces on it add up to zero. The force that tends to move it one way is equal and opposite to the force that tends to move it the other.
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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 is greater because it gives a greater force on the water plug and pushes it into the air column.
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Measure the length of the air column.
What is the length of the air column?
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The air column is about 28 centimeters.
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How far would the water plug have to move to make the air column 10% shorter?
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It would have to move 2.8 cm to make the air colu,mn 10 % shorter.
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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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I squeezed the bottle at about a 8 out of 10 and achieved 10 % of the air column, or 2.8 centimeters.
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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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A squeeze of 2 made it change by about 0.5 cm, which is about 1.8 % of the air column length.
A squeeze of 5 made it change by about 1.5 cm, which is about 5.4 % of the air column length.
A squeeze of 8 made it change by about 2.8 cm, which is about 10 % of the air column 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 heated the bottle with a hairdryer and was able to make the air column raise by about 2.8 cm, or 10 %.
When it cooled it dropped about a cm, which was about 2.8 % of the 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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The volume of the air in the capped botted decreased by about 50 %.
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Estimate the percent change in the number of molecules in the air within the capped bottle.
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The number of molecules remained the same because they were pushed back into the bottle, just with a smaller volume.
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Estimate the percent change in the volume of the water in the open bottle.
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The percent change in the volume of water in the open bottle is about 50 %.
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What do you think is the percent change in the air pressure in the capped bottle?
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The percent change in the air pressure in the capped bottle is it increses by about 10 %.
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What is the difference in the two fluid levels?
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The fluid level in the capped bottle is about the same as in the open bottle. The water levels are equal.
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What is the percent change in the number of air molecules in the capped bottle?
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I do not believe the number of air molecules changed because the system is closed. The volume decreased but the air molecules are still there.
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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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There is now about 70 % of the volume occupied by water.
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Estimate the percent change in the number of molecules in the air within the capped bottle.
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Since the bottle is capped, there is no change in the number of molecules. The volume may be decreased but the same amount of molecules are there.
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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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I think the pressure exceeds the original pressure by about 70%, because pressure if inversely proportional to volume and volume was decreased by 70%.
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What percent of the uncapped bottle do you estimate is now occupied by air?
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The uncapped bottle is occupied by about 70% of air because that much water left.
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What is the difference in the two water levels?
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The difference in the two water levels is about 6.5 cm, with the capped bottle gaving more.
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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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The water levels are now equal again, since they are both on the same level.
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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 pressure in the uncapped bottle is about the same since it is open to the atmosphere and not a closed system.
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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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With the cap on, I could raise the water all the way up the tube, with a force of about 5 for the squeeze. This was about 48 cm. With the cap off, it would not raise above the water level.
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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 Column height
1 2.5 cm
2 6 cm
3 14 cm
4 30 cm
5 48 cm
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&#Good responses. See my notes and let me know if you have questions. &#