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In article om, wrote:

wrote:

Sailplaners will have a good understanding of natural air flow.
This text seems to suggest that you can take an unenclosed 'parcel'
of air, and move it through the surounding air, like you can throw
a solid object through the air.
== Chris Glur.

Chris,
What is happening is that the parcel has momentum, which is conserved.

All momentum is conserved.
But the molecules escape from the 'parcel' since it's not sealed.
So the combined system conservs momentum.

The momentum vector remains intact in the air until it is dissipated by
friction. Think of it as billiard balls passing along the momentum.

This is valid for each molecule.
The macro model is more complex.

Jim Ketcham

For the physicists: what's the AVERAGE velocity of the nitrogen
molucules at 25 degree C & atmospheric pressure ?

Now I know what they mean by "herding cats".

== Chris Glur.