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We have learnt some basic concepts of mass in the previous chapter.

**Mass**:

The Mass of an object is the measure of its inertia. We have also known that the greater the mass, the greater is its inertia. The mass remains the same whether the object is on the moon, earth, or outer space. Thus, the mass of an object is constant, and it does not change from place to place.

**Weight**:

We learnt already that the earth attracts every object with force, and this force depends on the mass of the object and the acceleration due to gravity. The weight of an object is the force with which it is attracted towards the earth.

Let us consider an apple placed over a weighing scale. The weight of the apple is due to its mass, and is acceleration due to gravity. We will assume \(m\) be the mass of the apple and \(g\) be the acceleration due to gravity.

According to Newtons second law of motion, the force acting on an object is given by

$\begin{array}{l}F=m\times a\\ \mathit{The}\phantom{\rule{0.147em}{0ex}}\mathit{acceleration}\phantom{\rule{0.147em}{0ex}}\mathit{due}\phantom{\rule{0.147em}{0ex}}\mathit{to}\phantom{\rule{0.147em}{0ex}}\mathit{gravity}\phantom{\rule{0.147em}{0ex}}\mathit{is}\phantom{\rule{0.147em}{0ex}}\mathit{taken}\phantom{\rule{0.147em}{0ex}}\mathit{as}\phantom{\rule{0.147em}{0ex}}g,\phantom{\rule{0.147em}{0ex}}\mathit{so}\phantom{\rule{0.147em}{0ex}}a\phantom{\rule{0.147em}{0ex}}\mathit{is}\phantom{\rule{0.147em}{0ex}}\mathit{replaced}\phantom{\rule{0.147em}{0ex}}\mathit{with}\phantom{\rule{0.147em}{0ex}}g\\ F=m\times g\to 1\end{array}$

The force of attraction of the earth on an object is known as the weight of the object. It is denoted by the letter \(W\).

Substitute \(W\) in equation 1,

$W=\phantom{\rule{0.147em}{0ex}}m\times g$

Therefore, the weight of an object is the measure of the force with which it is attracted towards the earth. The SI unit of weight is the same as that of force, that is, Newton, and it is denoted by the letter \(N\). The weight is a downward-acting force that has both magnitude and direction. Near the earth's surface, the value of \(g\) is constant. As a result, the weight of an object at a given location is directly proportional to its mass. As a result, we can use an object's weight as a measure of its mass at a given location. An object's mass is constant everywhere, including on Earth and other planets, whereas its weight is dependent on its location.