For an object with constant mass, the net force acting on the object, is equivalent to the Mass of the object multiplied by the Acceleration.

An atomic system is comprised of particles (bodies with specific properties of Mass, Inertia), and subject to the laws governing forces acting upon objects. Each component of this system will have various possible motions it could take, and each motion is considered a state. Classically, one can describe this state via the coordinates of the system and the velocities of the components at some point in time, with the complete motion thus being determined.