If neither the object's speed nor its direction of motion
is changing, then the net force acting on it is zero.
There are two ways this could happen:
1). There are no forces at all acting on it.
2). There are two or more forces acting on it, maybe millions
of them, but their magnitudes and directions are assorted exactly
so that they all cancel each other, and the sum of all of them is zero.
Then, as far as the object knows, it's as if there are no forces at all
acting on it.
