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A French citizen, filling out a form, writes “78 kg” in the space marked Poids (weight). However, weight is a force and the kilogram is a mass unit. What do the French (among others) have in mind when they use a mass unit to report their weight? Why don’t they report their weight in newtons? How many newton’s does this person weight? How many pounds?

A French citizen, filling out a form, writes “78 kg” in the space marked Poids (weight). However, weight is a force and the kilogram is a mass unit. What do the French (among others) have in mind when they use a mass unit to report their weight? Why don’t they report their weight in newtons? How many newton’s does this person weight? How many pounds?

Grade:10

1 Answers

Jitender Pal
askIITians Faculty 365 Points
8 years ago
The mass is the quantity of matter that contained in the body. Qualitatively, the mass of a body is the opposition offered when a force tries to produce acceleration in it.
The weight (w) of an object is equal to the product of its mass (m) times the acceleration due to gravity (g). It is given as
w = mg
Therefore, the weight of an object is proportional to its mass.
The weight of the body depends upon the value of the acceleration due to gravity of the earth (g). The value of g varies from place to place on the surface of Earth. Thus, the weight of the body is different for different place, since the value of g is different at different places. But mass of the body will remain constant everywhere. It does not vary from place to place. Therefore, the mass of a body does not vary with changes in its local weight. Therefore, it is better to write the weight of the body “78 kg”.
If they report the weight of the body in newton, then it will vary from place to place on the surface of Earth as well as outside surface of Earth due to different value of g at different places. That is why they do not report their weight in newtons.
To obtain the weight of the person in newton, substitute 78 kg for the mass m and 9.81 m/s2 for the acceleration due to gravity g on the surface of Earth in the equation w = mg,
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