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Re: Balloons without gases...



On Mon, 3 Mar 1997, Richard E. Grandy wrote:

Greetings everyone. I've been working on a few labs dealing with
the gas laws when a thought occurred to me. Is it possible to make a
"floating" balloon without the use of any "light" gases (hydrogen,
helium, etc.)? What I was wondering, would it be possible to take a
rubber balloon like material and seal it all the way around so that air
cannot get in or out of the inside envelope. The inside lacks any air
(vacuum or near - vacuum). If the inside of this balloon had some sort
of light, strong rib material that flexes outward pushing the outer walls
so that the balloon has a greater volume. I know the pressure inside
will greatly decrease and the "skin" of the balloon will be "sucked"
inwards, but if it were rigid enough, could this work? Has it already be
done? Am I onto something that could bring me instant success and early
retirement? :-)

Dwight
Ashland, OH

Dwight--

I think this could bring you instnat success and early retirement. The
secret is in the "light but expanding to rigid" formula. Let's imagine

Since this phrase ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't appear above, I
gather it is your own interpretation of Dwights question.

that we get that material for the balloon, and that we add a valve to allow
gases to enter the balloon. We expand the light but rigid balloon and
ascend to height h, we then maneuver with negligible energy expenditure
over a lever and then open the valve. As we take in gas the balloon
depresses the lever and raise a weight on the other arm. Repeating the
process we raise as much mass as we like to height h and have a perpetual
motion machine.

Hmmm, I didn't see anything in Dwight's question to suggest that he was
under the illusion that the balloon could be expanded into its bouyant
state for free (the missing energy step in your proposal).

****

Dwight your proposal certainly sounds like it would work provided the
right materials could be found. That is a pretty "heavy" provision
though. The first question to pop to mind is whether balloon materials
themselves hold up very well to 15 psi (oops, I've slipped out of metric
mode). My recollection is that the excess pressure that they hold is
typically much less than atmospheric, but I don't have a source on hand.
Perhaps someone else has a number for the pressure difference that
would burst a balloon skin. In general, I'm sure we've all seen what
atmospheric pressure can do to fairly rigid materials. I used to do a
demo for elementary school kids where I boiled water in a big metal can,
then screwed the lid back on. It twisted and collapsed, but didn't float
up. Clearly you need what are on average much stronger and lighter
materials than a metal can provides. i.e. strong ribs and a balloon type
side.

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| Doug Craigen |
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| If you think Physics is no laughing matter, think again .... |
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