# What is Gravity

Gravity is a force that pulls all the matter together. The relation between the gravity and the matter is that they are directly proportional to each other. Gravity is not just the force of attraction between objects and Earth but it is an attraction that exists between all the objects everywhere in the universe. Isaac Newton invented the concept of gravity when he stated that the objects fall on earth due to the gravity on earth instead being going up and he stated that force of gravity on earth was the same force that keeps the motion of moon around the earth and motion of earth around the sun. The effect of gravity extends in space in all directions. It is only gravity that makes the stars clump together in galaxies. Gravity is a force of attraction that exists between any two masses , any two bodies and any two particles. The gravitational equation says that the force of gravity is proportional to the product of two masses m1 and m2 and inversely proportional to the distance between their centers of mass.

F=Gm1m2/r^2

Where G is called the gravitational constant . It has value of 6.6726 * 10^-11 m^3 kg^-1 s^-2.

Gravitational motion between earth and moon is :

F

moon/Fearth=(Mmoon/Mearth)(Rearth^2/Rmoon^2)

Various theories were given on gravity:

Kepler ’s Gravity(1605): he gave 3 laws of planetary motion

Every planet has an orbit which is an ellipse having sun at one of its two focus points.

A line joining a planet and the sun sweeps out the equal areas during equal intervals of time.

The square of the orbital periods of planets are directly proportional to the cubes of the major axis of the orbit.

Newton’s gravity(1687)

An object in a motion will remain in a motion and an object at a rest will remain at rest until an external force is applied to it.

Force exerted on any object is equal to the product of the mass of the object and acceleration.

To every action there is equal and opposite reaction.

Because of gravity we are able to stand or stay on the earth

Because of gravity rain falls onto the surface of earth rather than going upward

Waterfalls down to earth which can produce electricity