Is Mass Weight?

Written by tutor R Bruce N.

There is a lot of confusion between the terms – mass and weight. Somebody asks, “How much do you weigh?” and you say, “I weigh 75 kilograms.”


We use the term weight when really we mean “mass”. Mass is the amount of material in an object and has no relation to its weight.

Weight depends on gravity, and gravity depends on where you are. ‘Ever seen astronauts in space? Do they float and appear weightless? Did you ever see images of astronauts jumping on the surface of the moon?

This is because our mass may be the same on earth, in space, or on the moon, but our weight depends on the attraction force called, “gravity”.

All bodies that contain material have mass. How much they weigh is the gravitational force that attracts, or pulls on them. Even two people standing close to one another produce a very tiny attraction force because this force is called Universal Gravitation and it is found everywhere in the universe.

Our body is on the surface of Earth and, although we may be small, the Earth has a LOT of mass and produces the Universal Gravitational force we call weight. This force always draws towards the center of gravity of any two objects and so, our weight – which is a force – is always directed vertically downwards towards the center of the earth. Wherever you are on earth, top, side, or bottom, the force is towards Earth’s center. Gravity is the reason why penguins don’t fall off Antarctica!

So, if kilograms is really mass, then what measures weight?

Weight is measured in the Metric system in Newtons. Newton was a very clever guy who figures as a giant is science. We will ignore the old British Imperial system of pounds and poundals because the Metric system is more common nowadays and much easier to handle.

In the next piece we will talk about Newton’s discoveries and more about the relationship between mass and weight.

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