"John Flanagan" wrote in message
...
On Mon, 21 Jul 2003 02:05:39 GMT, Jeff Wisnia
wrote:

So what *is* the pressure in a typical rubber party balloon. IIRC, it
gets
*lower* as the balloon expands. I think it's the same with soap bubbles.

I suppose the pressure in one of those mylar party balloons must be
pretty
close to one atmosphere.

If the sides are not rigid it's always *exactly* atmospheric pressure.
If it expands either atmospheric pressure has dropped or the
temperature of the balloon has gone up.

Here's a question for everyone. Explain *exactly* the mechanics of
how and why a balloon floats :^)?

As I understand the physics, air is a fluid and the helium balloon being
lighter than the air around it floats just as a drop of oil will float if
released from the bottom of a volume of water.


Not as easy as one might think.

And a second one is why when you have a helium balloon in your car and
put the brakes on to stop, the balloon will float to the back of the
car instead of flying to the front like everything else. Again, what
are the mechanics that make it do so?

Again the air being heaver than the balloon the air has more mass. When
this mass is in motion, pressure is equal on all sides of the balloon. When
the brakes are applied the air inside the car keeps moving at the speed the
car was going until it hits the windshield. As air bunches up in the front
part of the car, there is more air pressure at the front of the car and less
at the back so the pressure in the front pushes the lighter balloon
backwards.

--
Roger Shoaf
If you are not part of the solution, you are not dissolved in the solvent.