Re: $2 a kilogram ?

[John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>]

On Sun, 10 Feb 2002, Herbert H Gottlieb wrote:

> ... why does Macy's fill their Thanksgiving Day parade
> balloons with helium under a pressure that is greater than the
> atmospheric pressure?

In order to give them some rigidity.  Fortunately it only takes a
tiny bit of overpressure ("gauge pressure") to do that *secondary*
job.  As a result the helium is not appreciably more dense than it
is at atmospheric pressure and it still easily manages to do its
*primary* job which is to displace air without weighing very much.

John Mallinckrodt      mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm