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| Newton's Universal Law of Gravitation |
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| Every particle of matter in the universe attracts every other particle with a force which varies directly as the product of their masses and inversely as the square of the distance between them. |
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| If m1 and m2 are the masses of two bodies separated by a distance d, then the force of attraction F between the two bodies is given by |
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| Where G is the gravitational constant |
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| If m1 = m2 = 1 unit and d = 1 unit, then, |
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| from equation (1) |
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| F = G |
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 The gravitational constant is defined as the force of attraction between two bodies of unit mass separated by unit distance. |
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| a) The value of G in the C.G.S. system is 6.67 x 10-8dyne cm2gm-2. |
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| b) The value of G in the SI system is 6.67 x 10-11Nm2kg-2. |
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| The force with which the Earth attracts a body towards it is called weight. |
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| W = mg |
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| Where 'W' is the weight, 'm' is the mass of the body and 'g' is the acceleration due to gravity. Weight is a vector quantity. |
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