Newton’s First Law of Motion States that: In the absence of a net force, a body at rest remains at rest, and a body in motion remains in motion indefinitely along the same straight line.
The implication being that the First law describes inertia. A body will not change its existing state of motion without a net force acting on that body. In other words, without an outside force a body will remain still if still, or, if moving, keep moving in the same direction at a constant speed.
