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| Mass and Weight |
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| Mass and weight are commonly mistaken as the same, but they are two different quantities. Now let us try to find out the differences between them. |
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| Mass of a body is defined as the amount of matter contained in it. The SI unit of mass is kilogram (kg). Mass is a scalar quantity. The amount of matter contained in a body does not change with time or from place to place i.e., mass of a body remains the same throughout the universe. However, two different bodies can have different masses. Mass of a body is measured using a pan balance. |
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| Weight is defined as the force with which an object is pulled towards the centre of the Earth. |
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| Weight of a body = force exerted by the Earth = mg (according to Newton's second law of motion) |
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| W = mg |
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| SI unit of weight is Newton. |
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| For example, the weight of a body having a mass of 1kg is |
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| W = mg |
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| W = 1x9.8 = 9.8 N |
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| We know that kg.wt is commonly used as the unit of weight. 1 kg weight is the force with which an object of mass 1kg is pulled towards the Earth. |
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| W = mg |
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| 1 kg wt = 1x9.8 = 9.8 N |
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| 1 kg wt = 9.8 N |
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| Weight is measured using spring balance. Weight varies from place to place as it depends on acceleration due to gravity. A body weighs more at the poles than at the equator and a body's weight will become zero at the centre of the Earth as acceleration due to gravity is zero at the centre of the Earth. |
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| Let m be the mass of a body on Earth. Its weight on Earth is given by the equation |
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| The weight of the same body on moon (Wm) is given by, |
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| Dividing equation (2) by equation (1) we get, |
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| But we know that Me =100 Mm and Re = 4 Rm. |
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 Earth. |
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