Why doesn't the sky fall?

[john tarpinian]

The sky has fallen, its resting on the ground.

--- Wayne Galligan <wgalligan at goodsonacura.com> wrote:

> SO..... in other words... Newtons theory about the
> apple falling on his head about sums it up....
> right?
> 
> WG
> 
>   ----- Original Message ----- 
>   From: randy10926 at comcast.net 
>   To: discussion at nsrca.org 
>   Sent: Monday, August 15, 2005 4:35 PM
>   Subject: Re: Why doesn't the sky fall?
> 
> 
>         At the top of a planet's atmosphere,
> particles are running around in all directions, at
> all of the various speeds corresponding to the
> kinetic temperature, and to the predictions of the
> Maxwell-Boltzmann distribution. Some of the
> particles will be headed upwards, some downwards,
> and some sideways. Some of them will be moving
> slowly, some at an average speed, and some very
> quickly. Whether a planet will hold onto an
> atmosphere will depend upon the motions of those
> particles which happen to be moving upwards at a
> much higher than average speed. If those particles
> are moving upwards at less than the planet's escape
> velocity (the speed which an object must be
> traveling at in order to escape the planet's
> gravity, and go off into space), then the particles
> will follow curved paths which are ellipses with a
> focus at the center of the planet, and will go up
> for a while, and then fall back into the atmosphere.
> (This discussion assumes that we are in the very
> outermost reaches of the atmosphere, where there is
> so little gas that the particles don't collide with
> other particles very often. If we were talking about
> a lower region, the particles would be deflected
> from their paths, and change their energies, so
> frequently that any discussion of motions which
> resemble orbital motions would be pointless.)
>         However, if the particles were moving
> upwards faster than the planet's escape velocity,
> they would follow hyperbolic paths which would take
> them out into space, never to return. Of course,
> only those particles which happened to be heading
> upwards at very high speeds would follow such paths,
> but as already discussed, there is a continual
> shuffling of particle motions and speeds, and as a
> result, in a short while, particles which did not
> originally have such motions would end up with
> motions identical to those particles which had been
> lost, and then those particles would also be lost.
> 
> 
>   Simple ain't it.
> 
>   Randy
> 
>     -------------- Original message -------------- 
> 
>     I thought it was time to stir the pot while we
> wait for the results from the Worlds.
>     Can anyone explain why gravity doesn't pull all
> the air molecules down to earth?  Are they lighter
> than space?  What is their mean speed?
>     I don't think this will help answer the
> weathervaning question and won't help us fly any
> better but I thought it might be fun.
>     Jim O


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