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Universal Law of Gravitation

Newton's laws of Universal Gravitation

You must have heard the famous story of how young Isaac Newton, while sitting under an apple tree was struck on the head by an apple that fell from the tree. Scientists before Newton believed that things fell on the earth because it was an inherent property of matter and needed no further explanation. But Newton was not satisfied with this explanation. The incident of the falling apple set him thinking about falling bodies and led him to believe that there is a force of attraction between the body and the earth. It required the genius of Newton to realise that this attraction is only a particular case of a universal attraction between any two bodies situated anywhere in the universe. At the age of twenty-three he discovered a law, now known as Newton's Law of Universal Gravitation which states that,


"Any two bodies in the universe attract each other with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. The direction of the force is along the line joining the two masses."


Written in algebraic symbols, this law states that

where m1 and m2 are the masses of two objects, d is the distance between them and F is the force of attraction.


Gravitational force of attraction 
between two masses

The gravitational force F can be written in the form of an equation as

 N.       ------------- (1.1)

where G is a constant of proportionality called the Universal Gravitation Constant. From the above equation we get

Importance of the Universal Law of Gravitation : -
It helped to explain:

  • The force that holds objects to the earth,
  • The motion of the moon around the earth,
  • The movement of the planets around the sun and
  • The formation of tides due to the sun and the moon.

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