[Phys-L] Re: gas has mass

[Bernard Cleyet <anngeorg@PACBELL.NET>]

this is an easy problem if one make approximations and assumptions
[possibly extreme and invalid]

So I put on my freshman hat and came up w/ over 100 mph for two pieces
of a one litre bottle.  I'd been told compressed gas was rather energy
dense.  In the fifties a UCB lab was destroyed by a compressed gas
bottle when it fell and the valve was knocked off.  Since then I've
always screwed on the covers except when in use.  Also I purchased a
SCUBA tank to make a jet engine.  It and I on a dolly.

Here's my assumptions, etc.

isothermal and ideal gas (not bad here).

W =k (integ. 1/V dv)  limits 1 E-3 m^3  and 4.4 ....

k = 1/22.4 mole (8.3 J M^-1  K^-1) 300 K = 111 J

W = 164 J

Assume bottle splits into two masses of 50 gm.  Izod test of PETE is
0.5ft#/inch.  Six inch bottle, therefore, ~ 13.6 J. *

this leaves about 75 J for the projectiles.  Equating PE w/ ke  ~ 120mph

improvements:  treat the expansion as adiabatic.  somehow guess the
inefficiency ot the gas expansion to propelling the bottle halves.


Errors?

bc

p.s. *  probably rather less as the test specimen is wider (thicker)
than the bottle's

John Denker wrote:

> Weighing a two-liter soda bottle with 80 psig of air in it
> makes an unforgettable demo.  That's fifteen grams of air!
>
> Pleeease hydrostatically test your bottles and be
> careful with them.  Wear eye protection.  You don't
> want the bottles to go boom, especially not indoors.
> Guess how I know.
>
> Bottom half of
>    http://lists.nau.edu/cgi-bin/wa?A2=ind0502&L=phys-l&P=R4357
> plus
>    http://lists.nau.edu/cgi-bin/wa?A2=ind0502&L=phys-l&P=R2706
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