🚀 go-pugleaf

In article <1992Nov5.130316.28438@kth.se> e92_anh@vaxkab.lne.kth.se () writes:
>This will probably sound like a silly question to a lot of you, but WHY
>does a helium-filled balloon rise upward? Is it because of the
>difference in air-pressure at the balloon's top and bottom, causing the
>resulting force to press it upward?
>
>Thus, consider this: If the air surrounding the balloon had exactly the
>same density on all sides, then the balloon would not move (I think).
>
>So, is my airpressure-theory correct? I'd very much like to know!
>
>			-Andre' Heinonen, Royal Institute of Technology, Sweden


Yes, you are exactly right, it is the pressure differential (gradient), that
causes a balloon to float.  Note that bouyancy is predicted in the hydro-
static equations, even if one assumes a constant density fluid, with no 
spacial or temporal density variations.  Even for constant density fluids, 
a hydrostatic pressure gradient is required for static equilibrium in a 
gravitational field.

	-AIP