Newton's second law, sometimes called the fundamental principle of dynamics, although considered as an irreducible axiom of mechanics based on and validated by experience, might paradoxically depend on the energetic content of our cosmos, through the existence of a dynamical form of aether appearing, in the ancient theory of Fatio de Duillier and Lesage, as an explanation of gravitational forces. In such a framework, Newton's theory is an approximation valid for small velocities as it was the case in special relativity theory.