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

In fact, the Greeks measured the distance to the moon by parallax, which gives the distance in units of the earth's radius.

"Trust me. I have a lot of experience at this."
General Custer's unremembered message to his men,
just before leading them into the Little Big Horn Valley

On Fri, 29 Oct 2010, Rauber, Joel wrote:

He needs an estimate of R (the earth radius) as well??

MmG/R^2 = mg


Joel Rauber, Ph.D 
Professor and Head of Physics
Department of Physics
South Dakota State University
Brookings, SD 57007
605.688.5428 (w)
605.688.5878 (fax)

-----Original Message-----
From: [mailto:phys-l-] On Behalf Of Herbert Schulz
Sent: Friday, October 29, 2010 2:56 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] How did Newton estimate the Gravitational

On Oct 28, 2010, at 9:59 PM, Jack Uretsky wrote:

So Newton had a value for M_{E}G. He could estimate M_{E} from
knowing g
at the earth's surface.


I guess I don't understand this. How do you get M_{E} from
M_{E}G/r_{E}^2=g without already knowing the value of G? Maybe I just
missed something.

My impression is that knowing the value of M_{E}G by knowing r_{E} and g
at the surface of the Earth is all you need to estimate the period of
the moon around the earth and that pretty much agrees with measurement.

Good Luck,

Herb Schulz
(herbs at wideopenwest dot com)

Forum for Physics Educators
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