Air baloon float because of Archimedes' principle. Pressure inside the baloon balances external pressure + baloon surface elastic force any time. So if inner temperature is high enough air density inside is lower that air density outside.
pV = nRT mic 2011/6/11 David Jonsson <davidjonssonswe...@gmail.com>: > Hi > This obvious fact from hot air balloons and rising smoke is also the case in > constant volume. Just do the math if you can't see what I mean. > Imagine a ball on lying at rest in a box. This is equivalent of a cold gas. > All pressure from the ball is on the bottom of the box. The weight of the > ball is just added to the box. Now let the ball do very fast bounces up and > down. The box will not weigh as much as before because the ball is also > bouncing on the ceiling of the box with almost as strong impulse as it is > bouncing on the bottom. The box + ball weighs less. The faster the ball > moves the less time it spends between bounces and the less can it's speed > change. Speed change is time multiplied with gravitational acceleration and > the faster it moves the less the speed can increase and decrease between the > bounces. > The same must be the case for a gas. Gas is just a collection of small > balls. The same must be the case if the box is removed and the gas molecules > bounce against each other. Right? > I have written before about this on the Internet but only for tangential > motion but today I realized it must also be the case for vertical motion. In > tangential motion the centrifugal acceleration increases and thus makes > balls as well as gas molecules appear as having less weight. > From the garden of the Stockholm Observatory, > David > David Jonsson, Sweden, phone callto:+46703000370 > >
