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Weight vs  Mass

It may seem a bit silly but old pencils like me get really confused by things like mass and weight. They really do seem to be the same thing but they are not, are they ?

Under normal circumstances a 10 kg steel bar will have a weight of 10 kg and a mass of 10 kg. With a change of circumstance, however, these values change in relation to each other.



If we are using a spring type scale or one of those digital things we are actually measuring the gravitational pull on the object being 'weighed'.

We have learned that gravity changes in intensity depending upon where we are. The further we are from the centre of Earth, for instance, the lower the effects of gravity will become.

In the not too distant future we will be wanting to make measurements, relevant to Earth, on the Moon, Mars or even Pluto,

As each of these places has a different gravity each of our measurements will simply be of weight in that specific environment.

The weight of an object will change according to the prevailing force of gravity which looks at the ammount of matter in an object.

Mass is something that never varies. Each atom has a certain amount of matter in it and it matters not if our steel rod is down a well, up a mountain or on the moon, as it has the same matter in it it will always be the same mass.

The mass of an object must be measured on a 'Beam Balance' where the object to be measured is placed on one side of the balance and metal 'weights' of known values are placed on the other side until the beam if perfectly level.

The value of the combined 'known weights' represents the mass of the object being measured. This measurement is true in a gravity of 1, or of 3 or of .1 so long as nothing has been added to or cut from the 'weights'.

This is so because the prevailing gravitational force acts equally upon the object and the 'weights'.





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Grandpa Pencil looks at Measuring Things