# Mass and Weight

We will discuss here about the measurement of mass and weight of any object. When we look around we can see innumerable varieties of objects physically, which are known as substances ; from a tiny particle to a huge bolder, all these are considered as substances and can be perceived by our sense organs. Each substance is made up of some material and the quantity of material present in a substance is its mass.

If a cricket ball is powerfully hit by a bat the ball moves up. After reaching a certain height the upward movement of the ball ceases and it starts falling down to the Earth because it is due to the attraction of the Earth. The Earth attracts every object exists on and around it towards itself. This attraction is known as the gravity of the Earth. The force of attraction of the Earth on a particular mass of a body is known as the weight of that body.

The force of gravity on a body varies slightly from place to place on the Earth. On a hill top the gravity of a body will be lesser than on a plain land. If gravity reduces at any place due to its height from the centre of the Earth, the weight of a body also reduces at that place proportionately. So, weight of a body, measured in Mount Everest, will be lesser than its weight as measured in Delhi. Thus, the gravity of the Earth at its centre is zero and maximum on its surface. So if we go down to a mine the gravity will be lesser and our weight will decrease. But mass of a substance is always constant and it never changes with the change in gravity and place.

Note:

All stars and planets in the Universe have their own gravity, which is different from each other. The gravity of the Earth is six times higher than that of the Moon. So, an astronaut having body weight of 60 kg on the Earth will weigh only 10 kg on the Moon.