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Re: Which came first, mass or inertia?



I am no expert but:
The Principia was written in Latin. I haven't checked but I suspect that
the word "momentum" appears there, and is translated as "quantity of
motion". It may not be used until later however, because the Latin term
"vis mortua" ("dead force") was also used prior to the Principia for the
quantity mv, with "vis viva" (living force) being used for mv^2. There
was a debate as to whether mv or mv^2 was the correct "measure" of the
force. It was only after Newton that it was clear that mv comes from
force*time and mv^2 from force*distance, thus both are different
measures of force.

Newton was quite clear on the distinction between mass and weight,
though he defined mass as being measured by weight. I am not sure
whether Newton uses the term "inertia" in the sense of resistance to
being accelerated.
J. Epstein