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In the previous sections, we have learned the

**acceleration due to gravity**. In this section, we will discuss the basics of mass and weight and the differences between them.

**Mass**:

Mass is the fundamental property of a body. The mass of a body is defined as the quantity of matter contained in the body.

The

$\begin{array}{l}\mathit{Weight}\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}\mathit{Gravitational}\phantom{\rule{0.147em}{0ex}}\mathit{Force}\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}\mathit{mass}\phantom{\rule{0.147em}{0ex}}(m)\times \phantom{\rule{0.147em}{0ex}}\mathit{acceleration}\phantom{\rule{0.147em}{0ex}}\mathit{due}\phantom{\rule{0.147em}{0ex}}\mathit{to}\phantom{\rule{0.147em}{0ex}}\mathit{gravity}\phantom{\rule{0.147em}{0ex}}(g).\\ \phantom{\rule{0.147em}{0ex}}\\ g\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}\mathit{Acceleration}\phantom{\rule{0.147em}{0ex}}\mathit{due}\phantom{\rule{0.147em}{0ex}}\mathit{to}\phantom{\rule{0.147em}{0ex}}\mathit{gravity}\phantom{\rule{0.147em}{0ex}}\mathit{of}\phantom{\rule{0.147em}{0ex}}\mathit{the}\phantom{\rule{0.147em}{0ex}}\mathit{Earth}\phantom{\rule{0.147em}{0ex}}(\mathit{at}\phantom{\rule{0.147em}{0ex}}\mathit{sea}\phantom{\rule{0.147em}{0ex}}\mathit{level})\; =\phantom{\rule{0.147em}{0ex}}9.8\phantom{\rule{0.147em}{0ex}}m\phantom{\rule{0.147em}{0ex}}{s}^{-2}.\end{array}$

Weight is a vector quantity. The direction of weight is always towards the centre of the earth. The

**SI unit of mass**is a \(kilogram\) (\(kg\)).**Weight**:The gravitational force exerted on a body due to the earth's gravity alone is called the weight of a body.

Weight is a vector quantity. The direction of weight is always towards the centre of the earth. The

**SI unit of weight**is \(Newton\) (\(N\)).The weight of a body changes from one place to another on the earth's surface because it depends on the acceleration due to the gravity of the Earth (\(g\)). The weight of a body is higher at the poles than at the equatorial region.

Example:

If a person whose mass is \(50\ kg\) stands on earth's surface, his weight would be \(490 N\) (\(W\ =\ mg\ =\ 50 \times 9.8\)).

If the same person travels to the surface of the moon, he would weigh only \(81.25\ N\) (\(W\ =\ 50 \times 1.625\)). But, his mass remains the same (\(50\ kg\)) on both the earth and the moon.