GCSE SCIENCE PHYSICS HIGH SCHOOL - Forces and Motion - Newton's First Law - Balanced Forces

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Newton's First Law of Motion - Balanced Forces.

A force is a push or a pull. It is measured in Newtons (N).

If all the forces which act on an object along the same line
are equal and opposite,
then when you add them up they all come to zero
and the forces are called balanced.

Balanced Forces

The cube in the picture above has two forces pulling in opposite directions.
The overall force is 5 - 5 Newtons = 0 N. The forces are balanced.

Newton's First Law says that
If the forces on an object are balanced then it will carry on as it is.
This means that
(i) if the object is not moving then it will continue to stay still.
(ii) if the object is already moving
then it will continue to move with a constant velocity.

Part (ii) goes against common sense.
We know that in the "real world" things slow down and stop
if there is nothing to keep them going.
Newton understood that there is a force
which makes things slow down and stop. It is called friction.

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