A force is a push or a pull. Forces can make things start moving, stop, speed up, slow down, change direction or change shape. Forces are measured in newtons (N).
We draw forces as arrows. The arrow points in the direction of the force, and a longer arrow shows a bigger force.
When the forces on an object are equal in size and opposite in direction, they are balanced: a still object stays still and a moving object keeps moving at the same speed in the same direction. When they are unbalanced, the object's motion changes.