Re: Internal or external?

[Leigh Palmer <palmer@SFU.CA>]

At 03:30 -0700 10/11/99, Robert Carlson wrote:

> My question did not concern the reading of the scale at all.  It simply asked
> what the weight was.  In the Newtonian sense, and the definition given for
> weight in all introductory physics texts, the weight is 1000 N in all six
> cases.  What could be simpler than that?  At least once in your past
> postings, you have stated how important the use of language is.  Now, it
> appears you want to redefine weight.  I'll stick with the old definition in
> the Newtonian realm until your definition gains popularity in the
> introductory texts.  Good luck with your lobbying efforts.
>
> Bob
>
> P. S.  I do agree with you concerning the introduction of unnecessary
> terminology such as apparent weight.

If the conventional textbook definition is that the weight is 1000 N
in all three cases, then why do we need that concept at all? Is not
the mass of the object a complete description?

You enlist Newton as your authority for the conventional meaning of
weight. I would argue that the concept of weight predates Newton by
many centuries, and, further, that the concept has *not* been altered
by him. I would try to be more authoritative but I haven't the time
to comb the 2-2/3 pages in the old OED devoted to the word for
appropriate citations (Brian?). Certainly eighty-odd years after
Einstein fixed things up right we ought to be able to go back to the
earlier, simpler idea that is embodied in the OED definition:

   I. Measurement of a quantity by means of weighing; quantity
      (in the abstract) as determined in this way.

The conventional definition of weight seems to be the same as what I
prefer to call the gravitational force which acts on the object. I
note that a bathroom scale (in a nonflooded, nonaccelerating bathroom)
does not measure gravitational force. That would be magic! It measures
the force imposed upon it by the object resting on it. I make the
radical proposal that we call what the bathroom scale registers
"weight", and that we can do so without appealing to the law of
universal gravitation. Admittedly this solution also has some problems
in that it can't explain the dynamics of large systems (where the
Earth's curvature becomes important) or those with fast moving objects
(where Coriolis corrections must be made), but then neither does the
more conventional definition.

It seems to me that the only virtue of the conventional definition of
weight (if that definition in your text does indeed state that the
weight is invariant) is that it lends itself to simpler answers on
multiple choice tests. I see that as a barrier to understanding. My
textbook would have as few barriers to understanding as possible. He
clearly indicates that he is aware of the problems that give rise to
my objections, that this definition is gratuitously problematic.  It
may be that Hecht felt he couldn't go that far for market reasons.
That is the only reason I can think of for his convoluted (but most
conventional) approach.

Leigh