Re: Hot air rising and automobile thermometers

[Rick Tarara <rbtarara@SPRYNET.COM>]

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.

Rick
----- Original Message -----
From: Leigh Palmer <palmer@SFU.CA>
To: <PHYS-L@LISTS.NAU.EDU>
Sent: Monday, July 26, 1999 1:45 PM
Subject: Re: Hot air rising and automobile thermometers


> It should be recognized by physics teachers that winds, to first order,
> are not "driven" by anything. If a net force were present then a steady
> wind would be impossible; the wind velocity would vary in time. The air
> in a wind simply *seeks* to obey Newton's first law of motion. It moves
> with a velocity such that the net force acting is zero!
>
> The language being used here suggests that my earlier note about the
> equilibrium state went unnoticed by some. Physics teachers are making
> the classic student error of inferring the existence of a net force
> by observing the velocity of a body rather than from its acceleration.
>
> Think about it - again.
>
> Leigh