F = ma
There are two parts to this statement, one that predicts the behavior of stationary objects and the other that predicts the behavior of moving objects. The behavior of all objects can be described by saying that objects have a tendency to keep doing what they are originally doing.
For example, if there is an object with a mass of 4 kilograms. It is traveling at a constant velocity but is not accelerating. It will continue to travel at that constant velocity until acted upon by either gravity, friction or an external force.