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Radius of earth

I have two questions...

(1) How was the radius of earth calculated at the time of newton when he introduced the concept of gravitational force etc..,
(2) How is 'G' calculated without knowing the mass of earth?

venkateshwarr

ASKER

As you can see both the questions are interrelated.

SOLUTION

arantius

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venkateshwarr

ASKER

Thanks arantius.

I will keep this question open for couple of days to see if there are any other alternative solutions

venkat.

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d-glitch

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SOLUTION

d-glitch

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d-glitch

That should be radius and average density of the earth.

SOLUTION

ozo

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SOLUTION

grg99

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leojl

we flat earth people do not think this was a real question. leo

Talmash

u got lots of luck there wasn't internet and EE at those times ...

if internet was available that time, and you asked this question, you have been probably burned or at least crucified.

I think Ticho-Brahe's notes and Kepler's calculations led finally to evaluate G.

tal

ozo

No, Though Newton would have known G*(mass of the sun) from on them.

venkateshwarr

ASKER

Sorry for the delay in reviewing your comments...

Thanks

diegoful

Let's start with your second question. The gravitational constant G was actually measured experimentally by Cavendish with his torsion pendulum. Basically, he built a very sensible pendulum and hung large masses from it (large spheres of metal). The gravitational force between the spheres made the pedulum twist a little bit. As the mass of the metal spheres and the force was known, G could be derived from Newton's Gravitational Law. Here are some links about how exactly Cavendish did so:

http://www.physics.mq.edu.au/~dalew/Cavendish.html
http://www.npl.washington.edu/eotwash/gconst.html

About the first question, you can calculate the radius of the earth using very different techniques. Eratosthenes did it long, long time ago based on the shadows of objects. Here is how:

http://spaceinfo.jaxa.jp/note/shikumi/e/shi07_e.html

Also, you can do it if you already know the Mass of the Earth:

http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Mass.shtml
http://www.physchem.co.za/Motion/Gravity.htm#Acceleration

Regards,
Diego

n_vishwanatha

what i know the earth radius can be found by knowing the differance between the
time of two sun set...