Newton's first law of motion states:
Objects will remain at rest, or move with a constant velocity unless acted on by a resultant force
This means if the resultant force acting on an object is zero:
The object will remain stationary if it was stationary before
The object will continue to move at the same velocity if it was moving
When the resultant force is not zero
The speed of the object can change
The direction of the object can change
Applying Newton's First Law
Newton's first law is used to explain why things move with a constant (or uniform) velocity
If the forces acting on an object are balanced, then the resultant force is zero
The velocity (i.e. speed and direction) can only change if a resultant force acts on the object
