Le Chaud Lapin wrote in
ups.com:

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.


"My point is that you should strive to keep your instructions simple and
to the point. The people that come to an instructor for training are not
in the least bit interested in leaning th emathemaical equation that
keeps the airplane in an inverted turn. there only concern should be in
how to use the controls to get it there"


Bertie