Re: operational F, m, and a

[Jack Uretsky <jlu@HEP.ANL.GOV>]

Hi all-
        In general I agree with Michael.  But-
        I think that he is confusing the definition of units, where any
agreed upon standard is acceptable - just name your standard - with the
definition of a concept, as Denker has already made abundantly clear.
        The SI definition of the unit of force (the Newton), is the force
needed to accelerate a Kg of mass by 1 m/s^{2}.  So, given a concept of
force the SI definition tells me how to calibrate that concept.  Given
a set of masses and a standard mass and gravitational location
I can independently develop a concept of force without acceleration being
involved because I make only equilibrium measurements (ala Sommerfeld).
Then F=dp/dt is a non=trivial equality between two separately measured
entities.
        There are other ways of proceeding but each one must, in the
last analysis, involve a testing of the validity of N2 (which must, of
course, fail in certain limiting conditions).
                                                Regards,
                                                        Jack

On Tue, 16 Oct 2001, Michael Edmiston wrote:

> Jack Uretsky says:
>
> I try to teach my students that argument by authority
> is VERBOTEN!!!!!!
>
> In general I agree with Jack.  But not always.  On some issues we have to
> agree to respect the authority of persons or groups identified to decide
> things for the world.  That's the idea behind IUPAP, IUPAC, NIST, etc.  This
> is especially true when it comes to standards and units, but I think it is
> also somewhat true in terms of definitions.
>
> We can't have multiple definitions of SI units.  It would be chaos if we
> did.  It is less important to rid ourselves of multiple explanations for the
> concept of force, but it would be good to eliminate as much chaos as
> possible by agreeing on a definition... or... agreeing to accept the
> definition of some "authority."
>
> Or stated another way... we do have authority figures and authority
> organizations in science.  Therefore, when individuals like us get into
> e-mail discussions about these kinds of issues, why don't we do a little
> looking around to see what the "authorities" have to say about the issue?
>
> Authorities are not guaranteed to be right.  But the reason they are
> considered authorities is either because they were chosen to be authorities,
> or because they have established a good track record.  My investment advisor
> is not always right, but he has a heck of a better track record than I would
> have by myself.  Therefore I respect him as an authority for what I should
> do with my investment money (which unfortunately doesn't amount to much).
>
> Additionally, the question Robert Cohen is asking (about F=ma being a
> theory) is how common is this particular viewpoint.  We could approach this
> by randomly asking people we meet on the street, but I would think it much
> more productive to choose some people or some organizations who have
> established some sort of authority in this field, and ask them.  We on this
> list are some of those authorities.  But we are not the only ones.
>
>
> Michael D. Edmiston, Ph.D.              Phone/voice-mail:       419-358-3270
> Professor of Chemistry & Physics        FAX:                    419-358-3323
> Chairman, Science Department            E-Mail                  edmiston@bluffton.edu
> Bluffton College
> 280 West College Avenue
> Bluffton, OH 45817

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