Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Jim Logajan wrote:
You must have a devil of a time figuring out what keeps balloons afloat,
what with no handy downward moving air!
I have no trouble figuring that out at all. A gas of a different density
within the balloon causes the net upward force on the balloon exerted by
the air outside the balloon to be greater than the net downward force on
it.
Nope! The "gas of a different density" inside does not cause the
differential forces exerted by the air outside. Whether the balloon is
filled with phlogiston or concrete, the difference between upward and
downward forces exerted by the air outside depends on the height of the
balloon. That's what my goofy 10,000 foot thick wing was, that would
take off with no airspeed or power. A balloon.

You're wrong.

The "net downward force" includes the force of gravity. Which is
lessened because a gas of lower density..

...I can't believe I have to explain things so basic.

I know, but you have to. Your first attempt didn't appear to include
unsaid gravity. Gas that you described as "within the balloon" is now
treated as "part of" the balloon.