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How Newton found Gravitational acceleration (g) of The Earth?

Can you describe the methods to find and prove it(g value)?

(may be describe both classical methods and modern methods)

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2 Answers

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You can measure the gravitational acceleration with a pendulum and a stopwatch, which is how Newton did it. However these days it's measured to great precision using accelerometers aboard satellites. In particular the GRACE and GOCE satellites have measured the gravitational field of the Earth to exquisite precision.

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did Newton have a stopwatch? Galileo had to use heartbeats, but I think Newton might have had a pendulum clock. – Ron Maimon Nov 2 '12 at 17:07
Actually I'm not sure that Newton measured $g$, or at least not to any special accuracy. He did do experiments with pendulums (penduli?) but I think it was to show that different materials gave the same period. – John Rennie Nov 2 '12 at 18:02
I suspect you are right, but then I am not sure when "g" was measured, or by whom. Galileo probably had a crappy measurement like "8.9 $\pm$ .6 (Galileo armspans) per (Galileo heartbeat)^2 ". Maybe it was Huygens. He was designing clocks, I think. – Ron Maimon Nov 2 '12 at 18:07
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It's also easy to determine GM, the gravitational constant * the mass of the earth. What's very difficult is to measure 'G'.

Which is why the first attempts at measuring 'G' were called weighing the Earth, it was the 'M' they were interested in.

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