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course PHY 232
1/24 4:16 pm
Brief Bottle Experiment 1bThe Air Column as a measure of Pressure
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?
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It gets shorter by about 11-12%.
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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 decreases by about 11-12% as well since the diameter of the tube doesn't change only height and it's a linear relationship, i.e. V=h*π*d^2/4
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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 stays the same as they have nowhere to go, so 0%.
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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 also stays the same since it has nowhere to go, so 0%.
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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 increases since the volume decreases and they are inversely proportional. So if the volume decreases by 12% then the pressure increases by 1/0.88 or 13.6%.
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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 also increases in the bottle and it's probably about 1 or 2%
@& As long as the pressure in the bottle and the pressure in the air column are unequal, then assuming the ends of the water plug are at the same vertical level, the water plug will experience unqual forces on its ends and will accelerate.
If the water plug is stationary then the pressure is the same on both ends.*@
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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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When stationary these forces are eq & opp since the net force is 0.
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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 air column because it is being changed by a much larger percent from it's original state.
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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 in mine is 25.5 cm.
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How far would the water plug have to move to make the air column 10% shorter?
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25.5*0.1 = 2.55 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?
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I achieved the 10% change with 5/10 squeeze.
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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 : 3%
5 : 10%
8 : 15%
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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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Cold: +0.5 cm
Hot: -1.5 cm
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@& Good, but see my one note.
Now please take a minute and answer the following. Submit a copy of just these questions, with your answers, using the title 'follow brief bottle experiment 1b'.
By how many degrees do you estimate you heated the bottle?
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By what percent did the length of the air column change as a result?
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On a 1-10 scale, what squeeze would that correspond to?
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