I see it from the opposite side, when any enclosed object goes up in the air, the further it goes up the less pressure there is, or inward forces on, the outside wall. just the opposite of going down in water. whatever is inside will thus have greater outward forces in comparison to those opposing. physical principles are at work, including greater temperature = more pressure, less temperature = less pressure for a given gas/liquid. higher temperatures induce more velocity in gas molecules which in turn produce more pressure on a surface. simple physical/chem properties. dont get confused with a gas expanding or contracting, its really all about exciting the molecules into motion. a mole is a mole, one ounce of liquid helium can make up many pressures and volume in space depending on temperature.
