I want to come to Hugh's defence in a partial manner. While I don't
disagree with any of the specifics that John D. wrote; I do think he
came down a little hard on the "whatever the scale reads" definition;
which I regard as a nice *short-hand* way of stating exactly what John
D. states in his reference
"However, in a fair number of practical situations we can arrange that
these non-gravitational contributions are negligible, in which case the
weight can be well approximated by measuring the total downward force,
perhaps by letting the object rest on a spring-scale. (Of course the
scale should be at rest in the chosen reference frame.)"
So if I interpret "whatever the scale reads"; to mean exactly what John
D. states in his item 9, in the reference above; and certainly as
informed by his item 10. I see little to no problem with using it as an
operational definition of weight. And it is certainly what I mean when
I say weight is what the scale reads. And let me add in defence of
operationalism; operational definitions have an excellent pedagogical
virtue, for many if not most beginners, of being more easily visualized
in a concrete fashion than the esoterica of free-fall frames.
I imagine that the very carefully written, and well written I might add,
definition of weight found in the above reference is contrived (for good
reason) to agree with "what the scale reads" as interpreted in section 9
of the reference.
I'd add that I interpreted Hugh to be meaning all this. I don't know
that he did; but given the context of his participation on Phys-L over
the years I strongly suspect it and would give him the benefit of the
doubt.
I'd further add, as John D. pointed out, that "what-ever the scale reads
definition has a lot of provisos implicit with the statement if one is
to avoid the problems John D. mentioned. And we should be gently
reminded of that from time-to-time.
________________________
Joel Rauber
Department of Physics - SDSU