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

Newton read the classics. The Greeks knew the distance to the moon (and sun- I think it's in the standard history of math books). If Google doesn't help you find it, get back to me.

"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 Thu, 28 Oct 2010, Brian Blais wrote:


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. :)



Brian Blais

Forum for Physics Educators