Gravity

       Newton showed us that gravity is an attractive force that keeps every celestial object in the universe under it's grip.
ie., F=Gm1m2/r².The more the massive an object, the greater is the force of it's pull. A stone thrown up in the air comes back to earth due to its gravitational pull . The earth and moon attract each other. If mass of earth is mass 1 and that of moon is say mass 2 then the gravitational force between this two is directly proportional to the product of masses( mass 1× mass 2 ) and further this gravitational force between this two decreases as the distance between them increases. This is the reason why we see low ocean tides during full moon day. The interesting thing about gravity is that the pull of the gravitational force is a universal constant ie     6.67408×10^-11m³ kg^-1 s^-2.
         Newton invented the equations which could be used to find the orbits of the planets in solar system and fire rockets. Assume that you are travelling in a spaceship into deep  space where the influence of gravity is zero. If in that accelerating spaceship, if we drop a ball, it would fall down, as it would be on earth. In the moving spaceship acceleration makes the ball drop, while on earth, it is gravitational force.
          Later came Einstein who proposed general relativity theory which tells that the force of gravity that is perceived is due to curvature of space-time. Theory  says that gravity not only pulls at massive massive objects like moon and small objects like a football but also it affects spacetime. What gravity did was that it actually 'bent' or 'curved' or 'warped' the space-time fabric. Space-time became warped under the influence of gravitational force, thus destroying it's smoothness.
           He further showed that the warped space that is created due to the presence of massive bodies like the sun,  the earth, is actually nothing but gravitation. The most extreme example of this curvature of space-time is black holes from which nothing , even light cannot escape once it past the black hole event horizon.

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