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*From*: Jack Uretsky <jlu@hep.anl.gov>*Date*: Sat, 30 Oct 2010 13:30:10 -0500 (CDT)

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

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

Professor and Head of Physics

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} fromknowing 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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**Follow-Ups**:**Re: [Phys-l] How did Newton estimate the Gravitational constant?***From:*"Hodges, Laurent [PHYSA]" <lhodges@iastate.edu>

**References**:**[Phys-l] How did Newton estimate the Gravitational constant?***From:*Brian Blais <bblais@bryant.edu>

**Re: [Phys-l] How did Newton estimate the Gravitational constant?***From:*brian whatcott <betwys1@sbcglobal.net>

**Re: [Phys-l] How did Newton estimate the Gravitational constant?***From:*"Karshner, Gary" <gkarshner@stmarytx.edu>

**Re: [Phys-l] How did Newton estimate the Gravitational constant?***From:*Jack Uretsky <jlu@hep.anl.gov>

**Re: [Phys-l] How did Newton estimate the Gravitational constant?***From:*Herbert Schulz <herbs@wideopenwest.com>

**Re: [Phys-l] How did Newton estimate the Gravitational constant?***From:*"Rauber, Joel" <Joel.Rauber@SDSTATE.EDU>

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