Chronology Current Month Current Thread Current Date [Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

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

Yes, and I think credit should be given to Michell who made the beta version of the balance and gave it (indirectly) to C. just before he (Michell) died.

bc informs: copies of all the original papers were required reading by the advanced lab. students during his "reign", and admires HC for giving due credit.

Much of the info. of our various posts is contained here:

http://www.public.iastate.edu/~lhodges/Michell.htm

On 2010, Oct 28, , at 05:21, Karshner, Gary wrote:

Brain,
The French revolution hadn't happened. This gave us the metric system, plus Newton's calculus, Fluxion Theory, was based more on geometry then algebra we use today. In geometry the usual approach to calculations was to do it by ratio and proportion. The Gravitational constant doesn't appear until Boys measurements in the late 19th century. Cavendish experiment determined the density of the earth and not big G.
Hope this helps. Our twenty twenty hindsight often distorts the way we perceive history.
Gary

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of brian whatcott
Sent: Thursday, October 28, 2010 7:00 AM
To: phys-l@carnot.physics.buffalo.edu
Subject: Re: [Phys-l] How did Newton estimate the Gravitational constant?

On 10/28/2010 5:00 AM, Brian Blais wrote:
Hello,

A student asked me this question in class yesterday, and I wasn't sure (haven't looked at the Principia in a long time, but always found the arguments a bit hard to follow). I imagine he could do it from a rough estimate of the mass of the Earth, mass of the Moon, and distance to the Moon. With the Moon's period you could get a value for G. Is this how he did it? I know that the direct measurement wasn't done until later, by Cavendish.

Further, did he have any way of estimating the distance to the Sun? I
couldn't think of one that was available at his time, but he was more
clever than I. :)

thanks,

bb

I quickly reviewed Book 1 Section 12 and saw propositions given in the usual geometric way of that time, that an inverse square law for force operates between bodies in elliptical orbit depending on their joint masses and inversely as the distance squared. I did not see an estimate
for the scaling constant, but I had no time to spare. Is it
established that Newton gave this estimate?

Brian W