In the law of gravitation, the value of gravitational constant G plays a very important role. The value of G explains why the gravitational force between the Earth and the Sun is so great while the same force between two small objects (for example between two human beings) is negligible.
The force experienced by a mass ‘m’ which is on the surface of the Earth (Figure 6.7) is given by
ME -mass of the Earth, m - mass of the object, RE- radius of the Earth.
Equating Newton’s second law, F = mg, to equation (6.11) we get,
Now the force experienced by some other object of mass M at a distance r from the center of the Earth is given by,
Using the value of g in equation (6.12), the force F will be,
From this it is clear that the force can be calculated simply by knowing the value of g. It is to be noted that in the above calculation G is not required.