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| Gravitational Force between two Light Objects |
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| Let us now calculate the force of gravitation existing between two unit masses separated by a unit distance. |
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| m1 = 1 kg |
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| m2 = 1 kg |
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| d = 1m |
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| G = 6.6734 x 10-11 Nm2/kg2 |
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| This is a very weak force. |
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| To find Force existing between two objects of masses 60kg and 100kg separated by a distance of 1m: |
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| F = 40.04 x 10-8 N |
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| This is also a very weak force. |
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| From the above two examples, it is clear why we do not experience the force exerted by one object (on the surface of Earth) on the other. |
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| Let us now calculate the force of attraction between an object of mass 50 kg and Earth. The mass of the Earth is about 6 x 1024kg. The distance between the Earth and the object is approximately 64 x 105m. The force of attraction between the object and the Earth |
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| This force is strong, we cannot ignore it. |
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| Now let us calculate the force of attraction between Earth and the Sun. |
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| The mass of the Earth = 6x1024 kg |
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| The mass of the Sun = 1.99x1030 kg |
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| The distance between the Earth and the Sun = 15 x 1010m |
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| = 3.541 x 1022 N |
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| This force is very large and it is this force which keeps the planets in their respective orbits. |
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| Conclusion: Gravitational force between two objects of ordinary size is very small, while the force is very large when atleast one of the objects is massive. |
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| 1. What is the force existing between two spheres of mass 10 kg each placed 100 cm apart? |
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| Solution: |
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| m1 = m2 = 10 kg |
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| Distance d =100 cm |
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| G = 6.6734 x 10-11 Nm2/kg2 |
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| 2. Calculate the force of attraction existing between the Earth and an object of mass 50 kg placed on the surface of the Earth. |
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| Solution: |
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| Given the mass of Earth = 6 x 1024 kg |
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| Radius of Earth = 6400 km = 6400 x 103 m |
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| Mass of Earth (m1) = 6x1024 kg |
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| Mass of object (m2) = 50 kg |
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| G = 6.6734 x 10-11 Nm2/kg2 |
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| Distance between the object and Earth = radius of the Earth = 6400000 m |
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| F = 3.1281x109 N |
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