Re: [Phys-l] force conventions

[John Denker <jsd@av8n.com>]

On 10/27/2006 07:29 PM, I wrote:

> We can define
>   Fu = force exerted *upon* a body by the surroundings
>   Fb = force exerted *by* a body upon the surroundings.
>
> It is /conventional/ to write N2 in the form
>   Fu = m a                 [2]


I have a question purely about terminology.
 -- Are there conventional /names/ for Fu and Fb?
 -- Are there conventional adjectives that would permit
  distinguishing Fu from Fb more compactly than two
  complete sentences?

This is relevant to the discussion of centrifugal force, because
in a centrifuge there is an Fb-type force exerted by the payload
upon the structure of the centrifuge.

=========

FWIW, here is a summary of my attempts to find and/or coin suitable
names.  I will happily abandon these attempts if acceptable /conventional/
names exist.

-- I have heard one non-expert speak of Fu as the "active force" and Fb
 as the "reactive force".  Apparently this is supposed to make contact
 with Newton's law of action and reaction (N3).  However, this conflicts
 with the vernacular meaning of "active" (as opposed to inactive) and
 can be expected to create lots of misunderstandings due to negative
 transference.  This terminology is unheard-of in the physics literature.

-- If we go back to Newton's version of N2 (rather than N3) we find
 that Newton spoke of Fu as the force "impressed upon" a body by the
 surroundings.  Now the word "impress" has a natural counterpart, so
 perhaps we could call
        Fu --> Fimp = impressed force
        Fb --> Fexp = expressed force
 This terminology is AFAICT unheard-of in the physics literature, but
 it at least makes sense from an etymological point of view.  Also, the
 roots "im" and "ex" helpfully refer to non-arbitrary directions, unlike
 "action" and "reaction" where the roots lack any useful sense of
 direction.

================

I am quite aware that it is standard practice to focus attention on Fimp
to the near-exclusion of Fexp, but still IMHO it would be nice to have
names for these quantities, if only to help emphasize the distinction
between them.

Suggestions?  Comments?