  Learning

is

simple

and

fun!

Register now! Browse subjects

### Theory:

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

Weight is a vector quantity. The direction of weight is always towards the centre of the earth. The SI unit of 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.
The value of acceleration due to gravity on the moon's surface is $$1.625$$ $m{s}^{-2}$. This is about $$0.1654$$ times the acceleration due to the gravity of the earth.
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.