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Mass, Weight and Gravity

The standard unit of mass is the kilogram (kg), The kilogram is defined as being equal to the mass of the international prototype kilogram, which is a platinum-irridium cylinder, stored at the International Bureau of Weights and Measures in Paris.


Mass is the measure of matter an object has. This measurement of mass is not affected by gravity; a bag of sugar would still have the same mass on the moon and on earth. Weight on the other hand IS affected by gravity, the SI unit of weight being that of the Newton (N). Weight is defined as the gravitational force of attraction between the mass of the earth and the mass of a body. The weight of an object can be calculated from the equation:

W = mg

Where
W= Weight
m= Mass
g= Gravitational acceleration

Gravitational acceleration varies with distance from the earth’s surface, at sea level the gravitational acceleration has a value of 9.806 m s¯², and for most applications this is a sufficient value to work from. So to work out the weight of a bag of sugar which has a mass of 1Kg in Newtons we simply use the formula above and put in the values.

Weight = (m)1Kg  x  (g)9.806 m s¯²

Weight = 9.806 N


 

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