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LESSON NOTES
            • Universal law of gravitation: Every object in the universe attracts every other object with a force which is
            proportional to the product of their masses and inversely proportional to the square of the distance between them.
                 The force is along the line joining the centres of two objects.








                 Let two objects A and B of masses M and m lie at a distance of d from each other as shown in the figure.
                 Let F be the force of attraction between two objects. According to the universal law of gravitation











            • G is called a universal constant because its value does not depend on the nature of intervening medium or
            temperature or any other physical variable.
                      S.I. unit of G = Nm /kg
                                       2
                                    2
                      Value of G = 6.673 � 10  Nm /kg
                                         –11
                                                  2
                                               2
                (Found by Henry Cavendish)
            • Importance of universal law of gravitation
                Universal law of gravitation successfully explained several phenomena like:
                      (i) The force that binds us to the earth.
                      (ii) The motion of moon around the earth.
                      (iii) The motion of planets around the sun.
                      (iv) the tides due to the moon and the sun.
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