Re: Nomenclature: Normal forces

[Bob Sciamanda <trebor@VELOCITY.NET>]

My approach has been :
After digesting Newton's Laws,  we proceed to observe and recognize the
existence of certain forces in nature so that we may start to fill in the
LHS of N2 and see where this Newtonian mechanics might lead.  Our purpose
is purely "phenomenological" - ie., we do not attempt to erect any theory
of the mechanisms behind these forces, we seek only to model them
sufficiently to fit them into Newton's paradigm as vectors describing some
interactions among objects.

We then proceed to generate vectors to represent the forces of weight (at
this point only the earth's action-at-a-distance attractive pull) and
string tension (a line of spring-coupled masses can here be offered as a
conceptual model (only a crutch) to visualize a mechanism behind string
tensions).

At some point we recognize the existence of  "contact forces" between
objects in contact with each other.  These forces must involve very
complicated inter-molecular interactions which we cannot hope to
understand here and now (experts continue to investigate the details).
However, we will find it useful to decompose this contact force into two
perpendicular components: one perpendicular (or NORMAL) to the surface of
interaction and the other parallel to this surface.  Discussion then leads
to spring/mass (mattress) models of the normal component and "friction" as
at least a name for the parallel component . . . etc.

Applying this phenomenology to models of some simple situations quickly
shows the power of the Newtonian model, working only with a very meager
knowledge of nature's secret details.

Bob Sciamanda
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor
----- Original Message -----
From: "Brian McInnes" <bmcinnes@PNC.COM.AU>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, September 25, 2001 8:16 PM
Subject: Nomenclature: Normal forces
> . . .

> Take a block sitting on a horizontal table top (No, don't take it; I
want to
> talk about it.)
> There are two forces acting on the block: the gravitational force
exerted by
> the earth and the contact force exerted by the table surface.
> . . .
> Brian McInnes