I have gone over this with brother more than a few times. We have fun at lunch discussing various things and seeing if we can answer the questions that arise. If there are any AOPA members out there we are the sort that hunger for the monthly “Test Pilot” Q & A’s.
So what we have been hashing out lately is what keeps the envelope of a hot-air balloon inflated.
And I mean inflated firmly. Before y’all jump on this we’re not talking about the buoyancy of the balloon in general. We are the both of us fairly well versed in physics and math and understand the dynamics of lighter-than-air-craft. Our question is from whence the pressure differential in the envelope? Clearly the fabric of the envelope is in tension and that tension comes from a higher pressure from within the envelope. The trouble of the question comes from the fact that the bottom of the envelope is open to the atmosphere.
If a pressure differential exists sufficient to keep the envelope tightly inflated, how come it down run out da hole at da bottom?
And please, for the love of God, Don’t give any anthropomorphic explanations about air molecules and say “they just wanna rise!”