Re: Hot air rising and automobile thermometers

[Leigh Palmer <palmer@SFU.CA>]

> But Leigh, surely a steady wind experiences more than one force.  While the
> net-force should be zero, the current question really addresses the
> 'driving' force, the one that keeps the air moving in spite of the
> 'frictional-type' forces which must also be present.  Indeed, if there were
> no such driving force the motion of the air would soon cease.

There is more than one force acting, but there is no frictional force.
Given a piece of air in a steady wind the immediately adjacent air is
moving at the same speed. By "to first order" I mean considering no
wind shear. The conventional explanation of geostrophic winds is of
first order. In this case the net force is zero. The force due to the
horizontal component of the pressure gradient is exactly balanced by
the horizontal component of the Coriolis force. Of course more forces
are present in real situations, but those are the two large forces.

When you have internalized this idea you will be one step farther
from the seductive Aristotelean construct, that force impels motion,
which seems to follow us around for years after we learn that it is
fundamentally incorrect. I have the same problem.

Leigh