Gene Nygaard wrote:
Well, perhaps you missed the fact that he was writing definitions for
a dictionary of _science_ ?

]
Yes, of science. NOt of the mechanics section of an introductory
physics textbook.

Is physics not science ?

Not quite, though you have a point. What we measure with a balance
is the relationship of the force due to gravity of the object we
want to weigh, to that of a reference object of a known weight.
We are measuring relations between "weights", as the term is
understood in physics. To illustrate this, in the absence of gravity
we could not measure mass in this way (well, we might contrive a way
to use inertial forces, but we'd still be measuring forces).

Pretty strange notion of what it means "to measure" something.

If I have measured forces, then suppose I weighed a gold coin on one
of these balances at Hammerfest, Norway, and it weighed 19 dwt 20 gr
(nearly a troy ounce; the troy units of weight are always units of
mass, never units of force). How much force is it exerting due to
gravity?

Then I take it to Quito, Ecuador, and it weighs 19 dwt 20 gr. How
much force is it exerting due to gravity here, where the acceleration
of free fall is much less?

If it makes it easier for you, change that to 30.84 g. How much force
does it exert at each place?

If we've measured forces, you should be able to tell me that. But we
haven't "measured" these forces.

Partly true. We have not measured their absolute values. We are not even
interested in them. We have measured the relationship between two forces,
which allows us to determine the mass.

We still depend on there being forces for this measurement to work.
Take your gold coin along on a flight on the Space Shuttle. In a
weightless state, your balance would not tell you anything, but
the coin would still have the same mass as in Hammerfest or Quito.

5.7.4 The use of the verb "to weigh" meaning "to determine the mass
of," e.g., "I weighed this object and determined its mass to be 5 kg,"
is correct.

If the weight and the gravitation are known, the mass can be determined,
so the above sentence is quite correct in any context, even as strictly
understood in physics.

Sure, introduce some new big "ifs" not in the original.

As in my example with the gold coin, usually the "gravitation" is not
known. Furthermore, "weighing" the object doesn't give you a "weight"
which is different from mass, as your statement assumes.

It might, and it might not, depending on the method of "weighing".
Use some kind of spring-based scales on your gold coin and it will.

The statement in that standard is intended to reflect the fact that
chemists especially, and physicists as well, consider the use of the
verb form acceptable in situations were many would not accept using
the noun "weight" to express the result when they "weigh" something.

Sure, an elaborate interpretation of what it was "intended to
reflect", to suit your purpose. Didn´t _someone_ just object
to introducing new stuff, not in the original ?

All the same, even in that context, those chemists and physicists
have a good reason for accepting one and not the other, which is
what my comment intended to point out.

CV