This is according to Newton's first law:
An object in motion stays in motion and an object at rest stays at rest unless an external force acts upon it.
When a forces are balanced, the object will either remain at rest, or continue in a single direction at a constant speed.
When it is unbalanced, the object will have accelaration, or a change in velocity. This means that the object will either speed up, slow down, or change direction.
