Re: inertial forces (definition)

[brian whatcott <inet@INTELLISYS.NET>]

At 17:32 10/18/99 -0700, Leigh wrote:
> > ... Newtonian viewpoint says, gravity is not one of these types of forces
> > since the gravitational is proportional to the gravitational mass of the
> > object.
>
> Was that Newton's viewpoint? Did he distinguish inertial and
> gravitational mass? He was aware that there is something funny
> about the gravitational force which seemed to act at a distance....

> I would appreciate a citation to answer my question. I believe
> I was taught that Newton meant the same kind of mass that he
> spoke of in his dynamics when he formulated his law of gravity....

> Leigh

I looked for a fitting text from Newton suiting the
 proposition that the gravitational force was proportional
 to the mass.

In the third book of the Principles, headed System of the World,
I can find this at the Scholium to Proposition 5, Theorem 5:

 "The force which retains the celestial bodies in their orbits
 has hitherto been called centripetal force; but it now being
made plain that it can be no other than a gravitating force, we
shall hereafter call it gravity..."

Proposition 6, Theorem 6
" That all bodies gravitate towards every planet; and that
weights of bodies towards any one planet, at equal distances from
the centre of the planet, are proportional to the quantities of
 matter which they sewerally contain.
....
[of pendulum bobs]
"And therefore the quantity of matter in the gold ...was to the
quantity of matter in the wood as the action of the motive force
upon all the gold to the action of the same upon all the wood..."

 A few pages later he tabulates the length of pendulums for equal
beat at different latitudes, and noting the difference, mentions
that the figure of the Earth departs from spherical.

 Still this is not the explicit distinction that Leigh has in
mind, I expect.

Sincerely

brian whatcott <inet@intellisys.net>
Altus OK