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MEASURING FORCES

The size of a force is measured in units called NEWTONS (N). We will get an exact definition of what a newton is later but for the moment you can get a rough idea of its size by thinking about the pull of the Earth on us. For example the pull of the Earth on one of your own class is probably between 400 and 550 N.

MASS

This is the amount of stuff (matter) in an object, it is measured in kilograms (kg) and is always the same wherever the object is. The only way to change the mass of something is to chip a bit off!

WEIGHT

We can all feel the earth pulling us towards the ground, we call this force of attraction our WEIGHT. The more massive we are the bigger is the force of attraction and the bigger is our weight. This also gives us a rough definition of the newton


A Newton is the pull of the Earth on about 100 g.
The pull of the Earth on 1 kg is about 10 N.

This means that if a girl has a mass of 42 kg the Earth will pull on her with a force of 420 N and her weight is therefore 420 N.

The mass of something does not alter but its weight may. On the surface of the Moon the pull of gravity if only one sixth of that on the surface of the Earth, on the Moon you would only weigh one sixth of what you do on Earth. On the Moon the girl in our example would still have a mass of 42 kg but her weight would be 70 N.



Student investigation
Use the Newton spring balances or Newton scales to find the force needed to:
A  Pull apart two pieces of glued paper   H  Open scissors
B  Turn twenty pages of your text book   I  Open a drawer
C  Push a drawing pin into wood   J  Open a pencil case
D  Pull a small stool across the floor   K  Turn on a water tap
E  Pull a wheeled stool across the floor   L  Rip paper
F  Pull down the board projector screen   M  Throw a shuttlecock
G  Pull the top off a pen   N  Pull sellotape off itís reel
 
 
 
© Keith Gibbs 2011