Re: How much gravity is on earth ? and does it depend onthe size of earth?

Questions:	How much gravity is on Earth? And how does it depend on the 
size on Earth?.

Answers:   	I will take it for granted that your question ought to have 
been phrased as "What is the gravitation force between an object and the 
Earth? And the relationship of the latter with size (that is, "mass") and 
distance (that is, distance from the center of the Earth to the center of 
the object)?.
	
The Earth exerts a downward gravitational force on an object near its 
surface. The gravitational pull of the Earth on the Moon, for example, 
keeps the Moon revolving around the Earth just as the pull of the Sun keeps 
the Earth revolving around the Sun (Reference: "Principles of College 
Physics by Shortley and Williams"). Forces of attraction between two bodies 
on Earth is related to the following expression:   ; where R is the 
distance from the center of the Earth to the particle or object; mE is the 
mass of Earth and m is the mass of the referenced object.

On the other hand, gravitational constant G is equal to 0.000000000000667 
Nm2/kg2 . The extremely small magnitude of G shows that the gravitational 
forces between bodies on the Earth's surface are extremely small and quite 
negligible. Please be careful; the quantity G is very different from the 
gravitational acceleration, g, which is 9.8 m/s2. 

The approximate radius of Earth is 6400000 meter. At a particular location 
near the Earth, the gravitational acceleration is constant in magnitude and 
direction. At or near the Earth's surface the magnitude of 'g' is 
approximately equal to 9.8 m/s2 and g is directed vertically downward.

For your information, Newton's third principle holds rigorously no matter 
what the state of motion of the bodies may be. This principle holds in 
cases of action at a distance such as occur with gravitational forces.