Greek astronomer Hipparchrus years ago. It is very interesting to note that in order to measure these distances he used only high school geometry and trigonometry. These details are discussed in the astronomy section ( . ).
Note . . Gravitational Constant 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 . ) is given by F GM m ( . ) M E -mass of the Earth, m - mass of the object, R E - radius of the Earth. Equating Newton’s second law, F mg = − , to equation ( .
) we get, = − mg GM m g GM ( . ) - - - - Unit Gravitation . Earth are not physically in contact with each other, there exists an interaction between them. This is because of the fact that the Earth experiences the gravitational force of the Sun.
This gravitational force is a non- contact force. It sounds mysterious that the Sun attracts the Earth despite being very far from it and without touching it. For contact forces like push or pull, we can calculate the strength of the force since we can feel or see. But how do we calculate the strength of non-contact force at different distances?
To understand and calculate the strength of non-contact forces, the concept of ‘field’ is introduced. The gravitational force on a particle of mass ‘m ’ due to a particle of mass ‘m ’ is F Gm m =− ( . ) where is a unit vector that points from m to m along the line joining the masses m and m . The gravitational field intensity E (here after called as gravitational field) at a point which is at a distance r