On Oct 8, 1:37 am, Jim Logajan wrote:
Le Chaud Lapin wrote:

It's what gases do. The particles are constantly bouncing away from each
other. This is pretty simple physics - something that should almost be
intuitive. If you have a cylinder of gas with an air-tight piston and pull
back on the piston and double the size of the volume do you seriously think
the gas will not expand into the other half as fast as it can to try and
stay in contact with the piston?

The gas will stay in contact with the piston. But the gas will not
stay in contact because of the piston head. It will stay in contact
because of the fixed cylinder wall and the molecules of the gas
itself.

To take your example further, let us suppose that you pop the top of
the cylinder so that the fixed head is no longer present. Let
pressure on inside equalize to pressure on outside. Now pull the
piston head again to increase the volume. The gas will follow the
piston head, but not because of the piston head. It will follow
because of the pressure of the molecules in the air bombarding each
other, causes some of the molecules to race toward the moving piston
head.

In other words, the piston head is not capable of exerting a force on
the air molecules that is in the direction that you just moved the
piston head. In order for it to be able to do that, there would have
to be an attractive force between the piston head and the molecules
that follow it. But there is no attractive force. The gas expands
because of intermolecular bombardment, and because of richochet from
the cylinder walls.

So one can say that, if you increased the volume in the chamber by
moving the piston head downward, the piston head does not exert a
downward force on any molecule that hits it.

If you are having this much trouble on a basic concept of gases, then I see
no value in you or anyone else investing time in dealing with your
questions, which you chose to post to an inappropriate newsgroup anyway.

Grumble. Now I recall why I had established a personal policy to stay away
from discussions of aerodynamics on this newsgroup: futility avoidance.

No trouble at all.

-Le Chaud Lapin-