Re: [Phys-l] How did Newton estimate the Gravitational constant?

["Karshner, Gary" <gkarshner@stmarytx.edu>]

Rick, 
	Your right about the mass of the earth. Newton assumed the density of the earth to be about five times that of water. Cavendish was impressed that he had gotten it close. Newton also didn't different between mass and weight as we do, although his measurements were capable of determining that difference. Before the wide acceptance of the metric system, standards of measurements' vary all over which is undoubtedly why they used ratio and not units.
	The history of units of measure is an excellent subject for a high school student.
Gary 

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Richard Tarara
Sent: Thursday, October 28, 2010 8:51 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] How did Newton estimate the Gravitational constant?

While I trust those with more historical background to be correct that Newton did not estimate 'G', I seem to remember that he did estimate the mass of the earth by estimating the average density.  (Any confirmation on that?)  With a number in hand for the earth's mass and the measured acceleration of a falling object (apple?), one could find a value for 'G'--if indeed the equation was ever written in that form.  I assume the units for such would have been 'interesting' at that point in time.

Rick

----- Brian Blais <bblais@bryant.edu> wrote:
> On Oct 28, 2010, at 8:21 AM, Karshner, Gary wrote:
>
> > Our twenty twenty hindsight often distorts the way we perceive history.
>
> yeah, I should have guessed that.  ;)
>
> as others pointed out, the geometrical methods primarily use ratios and the constant wouldn't come in.  it is interesting to imagine how one *might* estimate it, given only materials available in Newton's time.  clearly, if he felt no need (his methods produced useful results without needing it), it is likely he never estimated the quantity.
>
> thanks everyone!
>
> 		bb
>
> --
> Brian Blais
> bblais@bryant.edu
> http://web.bryant.edu/~bblais
> http://bblais.blogspot.com/
>
>
>
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