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

[Brian Whatcott <betwys1@SBCGLOBAL.NET>]

Perhaps I had better go into a few more details.
I expect any pressure vessel to stretch elastically, and hope not to
stray into the pressures where its expansion becomes non-linear.

Why is the calculated  density of air that I produced less than the
  accepted value?  The considerable expansion of the vessel should
give an apparent density greater than the benchmark

I was of course doing the demonstration at room temperature
where the density value benchmark is given at 0 degC

This accounts for a difference of about 293/273 or 1.07
Multiplying my number by this ratio does indeed place the density
  too high.

Brian Whatcott

At 09:58 PM 2/5/2005,  bc, you wrote:

[Brian]
> "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!


Brian Whatcott    Altus OK    Eureka!