JF Mezei wrote:

On 2017-12-25 20:29, Fred J. McCall wrote:

No, and in point of fact 'space' is generally not at 'zero pressure';
it is just very, very, very low pressure. There is typically 1 atom
of gas per cubic meter in space. Your 'blob of gas' is going to
dissipate to that level.

But is that not 0 PSI in terms of air not exerting any pressure against
any "wall" ?


No, it's not zero. It's just very, very low; 1.322 × 10-11 Pa.


On earth, gravity pulls air down whichn exerts 14.7 PSI onto the
ground/sea surface. On the ISS, the air exerts pressure against the
walls of the pressuve vessel.

But out in space, since the gas can expand to whatever it wants, is
there "pressure"?


Asked an answered. If there is gas, there is pressure.


Yes, if you have a ship with a flat front moving through a blob of free
floating air, pressure is created as it accelerates/hits those atoms.
But otherwise, is there really any pressure ?


Unless you are at absolute zero, gas molecules don't just sit. They
move around. That moving around is 'pressure'.


--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson