Gravitation

                   

           If we drop a stone from the roof of our house why it falls downwards? why it does not remain their or go upwards?

           So, their must be some force due to which it falls in downward direction & it was explained to us by the great scientist Isaac Newton which is popularly known as "NEWTONS UNIVERSAL LAW OF GRAVITATION"....

NEWTONS-UNIVERSAL -LAW-OF-GRAVITATION......

            According to newtons law of gravitation everybody in this universe attracts every oter body with a force known as gravitation and this force is directly proportional to the masses of these bodies and inversely proportional to the square of distance between them. The direction of force is lying along the line joining the centre of two bodies.

                        Suppose two bodies of masses m1 & m2 are lying at a distance of 'r' from each other. let the force of attraction between them be 'f'. Now according to newtons law of gravitation the force between them:

1) Is directly proportional to masses of two bodies i.e

2) And is inversely proportional to the square of distance between them.

                        f=Gm1m2/r*r

Where 'G' is constant and is known as universal gravitational constant. Its value remains constant anywhere in the universe.

FREE FALL:

                                    The falling of a body towards the surface of earth from a height due to gravitational force is known as free fall and such a body is known as freely falling body.

                        When a body falls towards earth we say that body is under free fall. Our earth attracts every substance towards itself e.g if a stone is dropped from the roof of house if falls towards the earth. earlier it was thought that lighter bodies take more time as compared to heavy bodies to hit the surface of earth but later on it was proved by the famous scientist Galileo when he drope two bodies different masses towards the surface of earth and both these stones hit the surface of earth at the same time. Later Robert boyle also performed an experiment to show the same thing.

           

ACCELERATION DUE TO GRAVITY (g):

            The uniform acceleration produced in a freely falling body is known as acceleration due to gravity. It is denoted by the letter 'g' and its value is 9.8m\s square. This value is not costant. For easy calculation it is sometimes taken as 10m\s square.

GRAVITATIONAL CONSTANT (G):

It is the value which was find out by newton in an experiment this value is used to calculate the gravitational force between two bodies it remains constant anywhere in the universe and its value is 6.67*10 raised power -11 and its s.i unit is nm square/kg square.

MASS:

                        Mass of a body is defined as the quantity of matter contained within a body. Mass of a body is defined by letter 'm' and its s.i unit is kg i.e kilo gram. The mass of a body does not vary from place to place. It remains constant everywhere in the universe and can be determined by pan balance or an equal arm balance. Mass is a scalar quantity it has magnitude but not direction.

            WEIGHT:

                        The earth attracts various bodies towards its centre which depends on the mass of the body and acceleration due to gravity at that place. The force with which earth attracts bbodies towards itself in the downward direction is known as weight. In other words the force of gravity acting on a body is known as its weight. Weight is denoted by letter 'w' and its s.i unit is kg/m square.