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Re: [Phys-l] History of MASS



Aaarrgh, I must retract much of what I said about Galileo in my
previous note. I'm not sure.

I stand by what I said about not being a historian, and having a
terrible memory :-).

Galileo "must" have grasped some sort of mass/weight distinction,
as evidenced by his experiments rolling stuff on inclined planes.
The non-verticality "dilutes" the force of gravity (weight)
without diluting the inertia (mass).

A related point: Newton said he quantified the mass/weight
relationship using pendulums ... following Galileo who very
thoroughly understood pendulums, and exploited them for many
purposes.

Newton was not kidding when he said he stood on the shoulders
of giants.

On the other hand, I still don't recall Galileo explicitly
drawing the distinction between mass and weight. The concept
or something like it "must" have been there, but I don't recall
the _terminology_ being there.

I put "must" in scare quotes, because I don't really know.
History is tricky. Sometimes historical figures, even when
(like Galileo) they are astonishingly clever, have "2" and
another "2" but don't put them together to make "4".

Newton did use the terminology /massa/ (mass) and /pondus/ (weight).
http://hypertextbook.com/physics/mechanics/newton-second/

Note that if you are going to be a historian, you have to check
the originals. Translations are notorious for putting modern
terms in the mouths of ancient writers who did not have modern
terminology at their disposal.

If you are interested in the terminology, it may be fruitful
to track the meaning of /massa/. The classical meaning was
"a lump, a mass" so the modern technical meaning must, at
some point, have been new. Did Newton coin the new meaning?
It wouldn't surprise me, especially given the way he started
using it, as if he wasn't sure whether he wanted to use the
term /corpus/ (body) or /massa/ (lump) to denote what we
nowadays call mass.

So, with apologies, we are back to the original question:

Galileo and Newton surely understood the need for such a
concept but when and why did it first arise?

I don't know, but it is quite likely that it arose gradually:
a bit of concept here, a bit more concept there, and
terminology somewhere else along the line.

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

Also, belatedly, I must ask: Why do you want to know? What
are you going to do with the information? Surely /most/ of
what we know about the mass/weight distinction came from
Galileo and Newton ... and I suspect looking much beyond
that will give rapidly diminishing returns.