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Re: inertial forces (definition)



Proposition VII, Theorem VII of Isaac's Principia is entitled:
"That there is a power of gravity tending to all bodies, proportional to
the several quantities of matter which they contain"

He thus perceived both the "force of inactivity" (below) and the force of
gravitation to be each proportional to the same property of an object: the
"quantity of matter". I don't think he saw anything striking in this; he
knew of no other force laws with which to see a contrast. Furthermore,
quantity of matter was the only defined, significant property of an
object; it seemed natural to describe the motion of an object, in a given
environment, completely in terms of this single property (this was also
Galileo's viewpoint).

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: brian whatcott <inet@INTELLISYS.NET>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, October 19, 1999 7:41 PM
Subject: Re: inertial forces (definition)


In considering Joel's cautionary note, I recalled that I had quoted
some fragments of Book 3, System of the World, without paying
attention to Newton's introduction to that book, where he mentions
his original intent (and manuscript) was to provide a popular
treatment "that it might be read by many..." but afterwards he
repented, for fear of giving rise to disputes.

He then reduced this book to the form of Propositions and suggests
prior reading of the Principles: if not all of them as being too
demanding, then at least the Definitions, the Laws of Motion, and
the first three sections of the first book.

Taking him at his word, I see that in the opening Definitions of
Book 1, the first mentions mass, the second the motion (momentum)
and the third discusses the "vis insita", the innate force of matter
which
"is a power of resisting, by which every body, as much as in it lies,
continues in its present state, whether it be of rest or of moving
uniformly forwards in a right line......Upon which account, this vis
insita may, by a most significant name, be called inertia
(vis inertiae) or force of inactivity."

So while Newton may not have distinguished inertial from gravitating
masses, he does write of distinct gravitating and inertial forces,
as I have shown here.

Brian



At 11:08 10/19/99 -0500, you wrote:
I'm not sure I would make such a bold statement as the one below.
There is,
of course, a difference between whether Isaac would've made the
distinction,
say in published and carefully written works...
Joel

Isaac himself would not have made the distinction between inertial
and
gravitational mass. This became most clear when Coulomb's law showed
that, by analogy, Newtonian gravitation involved a
"gravitational charge"...
Bob Sciamanda

Was that Newton's viewpoint? Did he distinguish inertial and
gravitational mass? ...
Leigh








brian whatcott <inet@intellisys.net>
Altus OK