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-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of John Denker
Sent: Monday, October 14, 2013 1:12 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] ? FCI --> momentum flow
On 10/14/2013 08:43 AM, Marty Weiss wrote:
Is diSessa saying there is no force between your butt and the chair?
OK, these are good questions, please keep 'em coming. The questions tell
me there are gaps in the story I'm trying to tell.
Just now I added a section that addresses this:
http://www.av8n.com/physics/force-intro.htm#sec-balanced-forces
There is a stack of books which sits on a scale, which sits on a table, which sits
on the ground.
This is an equilibrium situation. Downward momentum flows in a closed
circuit, upward from the earth to the books, downward through the scale,
downward through the table-leg, and back into the earth.
My students always ask where does it end?
It never ends. The momentum flows around and around, in a closed loop, a
closed circuit, with no net accumulation anywhere. This is characteristic of
equilibrium. For details and diagrams, see
http://www.av8n.com/physics/force-intro.htm#sec-balanced-forces
In my experience, students don't have a problem with this.
They have a pretty good intuition about conservative flow in a loop. If
anybody isn't happy with this, bring in a big round bowl of water and stir up a
rotational flow.
The water is conserved. The water is flowing, but there is no accumulation
anywhere.
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