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[Phys-L] Re: Weighing air (Was: electricity)



This reminded me of the thread that Ludwik started some years ago,
which involved plotting the decay of a screen wipe of radio-active dust.
One can easily see the virtues of the discovery method when one
gets enthused.

In this case, I reran the data with a (nom) 1 liter soda bottle, which I
could weigh better, and despite the smaller volume, got more
promising results, 1.27 gm/l as follow:

psig wt gm
0 62.7
5 63.2
10 63.6
15 64.1
20 64.6
25 65
29.5 65.5
36.5 66.2
47 67

Bottle wt (full) = 1137.6 gm

At the higher pressure (47psi) that I used here, it was obvious from the air
in the neck that the bottle appreciably swelled under pressure, when
initially full of water.

Brian

At 09:57 PM 2/5/2005, you wrote:
"Major uncertainty was the volume of the bottle."

that's what I thought too, until I plotted his (BOW) data, but a linear
fit is better than a power; the exponent is even sl. less than one!

bc

Is this what you'd expect for a perfect gas at const temp?


Brian Whatcott wrote:

Weighing an air bottle:

data
air temp 20degC, ambient pressure 29.93 in Hg
bottle wt full = 2.2 kg
empty = 75.9 gm
volume = 2.124 liter

air
press
psig bottle wt gm
32 81.8
25 80.4
19 79.5
17 79.3
15 78.6
12 78.1
9 77.6
0 75.9

Least squares fit
weight = [75.94 +-0.09] + air pressure X [0.183 +- 0.005] gm

For an air pressure of 14.7 psig excess wt is 0.183 X 14.7 gm
= 2.69 gm for 2.124 liters
= 1.266 gm/liter This is fairly respectable.
Major uncertainty was the volume of the bottle.

Brian Whatcott Altus OK Eureka!





Brian Whatcott Altus OK Eureka!