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| Torque due to Gravity |
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| Every particle of matter in a body is attracted to the Earth and the result of all these attractive forces is the weight of the body. |
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| Let w1, w2...... be the weights of a large number of particles of object whose total weight is W. |
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| Let the coordinates of each particle be (x1,y1), (x2,y2). |
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| Then the moment of particle 1 is w1 x1, particle 2 is w2 x2 |
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| The total torque is |
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| If the axes of reference are rotated by 90o, the total weight is unaltered. But, |
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| If we divide (1) and (2) by g, the equations become identical to the definition of centre of mass. |
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 The centre of gravity is the same as the centre of mass of any body. |
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