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

[Bernard Cleyet <anngeorg@PACBELL.NET>]

"Major uncertainty was the volume of the bottle."


I thought so to until I plotted your (BW) data.  I expected it to curve
as a result of expansion of the bottle under increasing pressure.
Instead a linear plot is a better fir than a power one.  Not only that,
the exponent is sl. less that one!

bc



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!