From: "Chris Jackson" <duncan@frii.com>
To: <balloon@balloonhq.com>
Subject: Re: twists adding weight.
Date: Fri, 15 Sep 2000 02:04:05 -0600

Greetings, All.


>>>It would float so long as you didn't twist it much!  Each twist weighs
>down the balloon a bit more.<<
>
>Pardon my ignorance, but how can a twist add more weight to a balloon?
>Shouldn't it weigh the same regardless of what you do to it ?
>If the balloon has say, 2 grams of latex, no matter what you do to it,
>there is still only 2 grams of latex, yes?


This was a tricky one!  It took a while, along with a private response to
Joe, to figure this one out!

Yes, in fact, each twist *does* add weight to the balloon design!

(For those who are uninterested in Physics or Trivia, please ignore this
post.)

Each twist that is added to a balloon increases the pressure of the gas
inside it. (helium or air, it dosen't matter!)  If latex was an "ideal"
elastic (in terms of a Physics professor), then the increased pressure would
result in an equal change in the volume of the balloon.

Latex is *not* an "ideal" elastic.

When you are filling a latex balloon, you start out fighting the
un-tensioned balloon.  It takes a relatively large pressure to get the
balloon started.   Once you get that first bubble started, however, the
pressure necessary to continue the inflation is much less.  As the balloon
nears the maximum safe inflation point, the necessary pressure increases!

Meaning: When the balloon gets tight, you need to force in more air to get
it to expand!

This compression, this increased pressure, means that the same mass of latex
and air is displacing *less* of the surrounding uncompressed air.  It is
this displacement that makes a balloon seem light.  A helium-filled balloon
displaces a greater mass of air than the mass of the balloon and helium.
This excess displacement is what makes the balloon float.  If you could cram
in an extra few grams of helium without changing the size of the balloon,
(its displacement.) then the balloon would be a few grams heavier, and
wouldn't float as well. (if at all!)

When you twist a 260, you decrease the displacement of the balloon without
reducing the mass.  This is why an added twist actually *does* add weight to
a twisted balloon.  If anyone with access to a jeweler's scale (the most
accurate kind of scale I know about) and an interest in providing empirical
evidence wants to help me out here, I would *love* to hear some actual
numbers.  Weigh the inflated balloon both before and after twisting, and
send me the numbers.

Thanks

Chris Jackson
Ft. Collins, CO.