Weight or Mass! What’s the difference???


Confusion hits us all when we start discussing weight and mass. Aren’t they the same thing??Well actually….not really! 


Mass is a measure of how much matter there is in an object. Mass is measured in kilograms.

SO an object for example a can of coke has a mass of 100 kg. It means this makes it heavy enough to show a weight of 100 kg.

Weight is caused by gravity. An object’s weight is how hard gravity is pulling on it. We think the weight is the same everywhere because we all live on Earth  BUT if it where in orbit it would not push the scale at all because there is no gravity. The scales would show 0 kg but the mass of the object will not change, it will still be 100 kg!

Depending on where you and according to the gravitational pull, the scales will show something different. Click on the image to see how scale measurements would look on different planets!

An object’s mass doesn’t change (unless you remove some) but it’s weight can change depending on where it is weighed.


WEIGHT IS  the effect of the pull of gravity on a mass; the measured heaviness of an object.

So Why Do People Say Weight instead of Mass?

People often use “weight” to mean “mass”, and vice versa.

Because gravity is pretty much the same everywhere on Earth, we don’t notice a difference.

But remember .. they do not mean the same thing,
and they can have different measurements.

Here are some conditions where the Weight might change:

  • in space – can be weightless
  • on the moon and other planets
  • you can even get very slight differences in weight in different locations on earth


WEIGHT should not really be measured in kilograms. What??? Yes, it is technically wrong to measure weight in kilograms, even though we weigh ourselves on scales which show kilograms. It’s a bit like when we refer to a tomato as a vegetable, it’s not, technically it is a fruit! Really!


Weight is technically a force, and the correct unit for measuring a force is the

NEWTON (=1 kg·m/s2) which is abbreviated N. It is named after Isaac Newton who discovered it after an apple fell on his head. 🙂


Gravity makes a 1 kilogram mass exert about 9.8 Newtons of force, so a mass of 100 kg really weighs about 980 Newtons on Earth.

why don’t scales use newtons?

It’s because people understand kilograms and grams best and it makes it easier for us to calculate. 😉

Hope this made things a bit clearer.

Till next time…

Peppi Orfanogianni

Go to http://www.mathisfun.com for more information and great explanations.

Images downloaded from the internet.

Featured image downloaded from http://www.i.ytimg.com and modified.

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