Originally Posted by
Ninthace
I beg to differ. As it loses buoyancy Archimedes loses the battle with Newton. As it descends increasing pressure, courtesy of Boyle, will compress the fixed mass of gas further decreasing the buoyancy and accelerating the descent and resulting in a fearsome bump. The only question is would the rising temperature at lower altitude bring Mr Charles to the rescue?
High altitude balloons are launched with a bubble of gas that is pretty small in volume compared to the volume at height, as the gas expands with reduced pressure at altitude. What counts is the displaced mass of the air the lifting gas replaces. Air masses (at sea level) 1.225 kg/m^3, helium 0.178 kg/m^3, so provides about 1 kg/m^3 of lift.