Re: Which came first, mass or inertia?

["Bob Sciamanda" <trebor@velocity.net>]

Tom wrote:
> . . .
> Does anyone know if the concept of mass, as
> the quantity of matter, preceded the notion of inertia?  I know that
weight
> has been used since the dawn o' man but what about mass?
All right!  you got me to dust off my copy of Isaac!
The opening words of the Principia (Prometheus version) are:

"DEFINITION 1
The quantity of matter is the measure of the same, arising from its
density and bulk conjunctly. . .
It is this quantity that I mean hereafter everywhere under the name of
body or mass.  And the same is known by the weight of each body;  for it
is proportional to the weight, as I have found by experiments . . ."

> On the same topic, does anyone know, in modern language, how Newton
> introduced momentum as the "quantity of motion?"  and did he derive the
Law
> of Conservation of Momentum and if he did, did he call it that?

Isaac continues:

"DEFINITION II:
The quantity of motion is the measure of the same, arising from the
velocity and quantity of matter conjunctly."

.. . .
> . . .
> Tom McCarthy


Apropos to the notion of inertia, there follows directly:

"DEFINITION III:
The 'vis insita' , or innate force of matter, is a power of resisting, by
which every body, as much as in it lies, endeavours to persevere in its
present state, whether it be of rest, or of moving uniformly forward in a
right line.  This force is ever proportional to the body whose force it
is; and differs nothing from the inactivity of the mass, but in our
manner of conceiving it. . . . "
>
When time allows, I'll look into his treatment of momentum conservation
(I invite you to beat me to it!).

Bob Sciamanda
Physics, Edinboro Univ of PA (ret)
trebor@velocity.net
http://www.velocity.net/~trebor