On 11/18/2003 09:09 PM, Ludwik Kowalski wrote:
> 1) What is gained by replacing the concept of static
> force (see my original message below) by the
> concept of "flow of momentum?"
On 11/18/2003, John S. Denker wrote:
> Answer:
> a) We gain some clarity. In particular it is hard
> to speak about "the" force at a given location in
> space, because for instance at the boundary between
> A and B there will necessarily be _two_ forces, one
> associated with the A side of the A/B boundary and
> one (equal and opposite) associated with the B side.
> Which is "the" force at that location?
Clarity about forces can (nay, must) be achieved by
identifying in every case _which body is acting on which
other body_ -- cf. N3!!! This preempts any confusion
about "the" force at the A/B boundary. It also reminds
one of the need to identify clearly the boundaries between
various parts of a system, and hence distinctions between
"internal" and "external" forces (or momentum flows).