Is antigravity a bunch of hot air?

Jim writes:

> Something puzzles me about the hot molecule and cold one. The random motion model is fine for engineering -the hot molecule has more so is less dense. The effect is easy to see but the cause is not. What happens to the cold molecule to make it hot? I think this is the question that is not addressed here. Somehow the hot molecule is energized. I don't think it is explained how this happens in rereading the posts so far.

Faster speed is the manifestation of temperature for air molecules. It is possible that the higher-energy collisions that a faster molecule experiences also do something to its interior, but that is not relevant to the lift provided to a balloon. That comes entirely from the mean speed of air molecules, and their inevitable sorting, with the fastest movers rising to the top. -|Tom|-

I agree with this view and even without the ballon. The idea I am wondering about is the difference in the two states of a hot and cold molecule. The difference is the hot one has more mass/energy that is caused somehow that is not explained by any current theory as far as I know(which is not all that far) What is the cause of the effect?

> [Jim]: The idea I am wondering about is the difference in the two states of a hot and cold molecule. The difference is the hot one has more mass/energy that is caused somehow that is not explained by any current theory as far as I know (which is not all that far) What is the cause of the effect?

The speed of the molecule is the main difference. The faster molecule has more energy because of its faster speed. [E = 1/2 m v^2] If a molecule gets hit from behind and gains speed, that makes it "hotter". The moleule that hit it and bounced back at a slower speed became "colder". -|Tom|-

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Faster speed is the manifestation of temperature for air molecules. It is possible that the higher-energy collisions that a faster molecule experiences also do something to its interior, but that is not relevant to the lift provided to a balloon.

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The rotational and oscillational degrees of freedom do also get their share of energy from "temperature". There are some forms of "heating" that preferrably affect rotational and oscillational exitation, e.g. a microwave oven... But all degrees of freedom tend to share the energy evenly when left alone.

I'd say that this thread amazes me completely. It shows how we tend to forget the basics of physics. It's not the hot air that pushes up - it's the denser media around that tries to fall below due to greater gravitational pull (or push - in particle gravity). So the greatest lift force comes from an evacuated "baloon" if you can preserve its volume by making it rigid to withstand pressure imbalance. Or use hydrogen or helium, like in older/later zeppelins, as those are lighter at the same pressure.

OK the faster molecule(rotation, vibration, or speed) is energized how? I know the contact with another molecule will cause one to cool. What is added to the first molecule from outside the model to cause to heating in the first place? This is a bit like the Abbot and Costello skit. But, it ain't baseball so just try to see there is something that caused the first molecule to speed up and what is it that cause?

> [Jim]: there is something that caused the first molecule to speed up and what is it that cause?

That's easy -- solar radiation. If there were no heat continually being added from the Sun (and a bit from radioactivity within the Earth), the atmosphere and everything else would cool toward 3 degrees K (the minimum temperature allowed by the radiation of starlight). But the continual absorption of solar radiation keeps adding tiny impulses to the air molecules, which must radiate it away to remain in thermal equilibrium. But that equilibrium is reached at a temperature of about 300 K at this distance from the Sun, so the air molecules have a corresponding amount of mean speed.

This is also why the really light molecules such as hydrogen and helium escape into space, because their mean speed exceeds escape speed. But the heavier molecules have a mean speed below escape speed, and only a few of them escape into the Earth's "geo-tail".

For some other planet at some other distance from the Sun, the amount of solar heating, the mean speed of molecules, and the escape speed are all different. Hence, the atmospheric composition is different. -|Tom|-