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

• From: Jack Uretsky <jlu@hep.anl.gov>
• Date: Sat, 30 Oct 2010 12:16:10 -0500 (CDT)

R(E) has been general knowledge since antiquity. The Greeks were able to estimate it by measuring the distance at which a lighthouse first came into view.
Regards,
Jack

"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
Department of Physics
South Dakota State University
Brookings, SD 57007
Joel.Rauber@sdstate.edu
605.688.5428 (w)
605.688.5878 (fax)

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] 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
constant?

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.
Regards,
Jack

Howdy,

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)

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