In this work a new dynamics is developed, which is valid for all observers, and which establishes, among other things, the existence of a new universal force of interaction, called kinetic force, which balances the remaining forces acting on a body. In this new dynamics, the motion of a body is not determined by the forces acting on it; instead, the body itself determines its own motion, since as a result of such motion it exerts over all other bodies the kinetic force which is necessary to keep the system of forces acting on each of them always in equilibrium.