In this chapter, we see how Du Châtelet put her account two-pronged methodology for physical science, and her account of bodies and forces, to work in three specific cases of bodily action in physics: collisions, gravitation, and vis viva. All three were problematic and controversial at the time she was writing. We discuss her treatment of Newton’s laws of motion, and her commitment to mechanism as the sole means by which bodies act on one another. The chapter makes clear the continuity of Du Châtelet’s project throughout the Foundations. This is contrary to the “Received View” of the text, according to which the later chapters on “Newtonian physics” are detachable from the opening chapters on “Leibnizian metaphysics”. It is shown that the Foundations is unified by its central concern – the problem of bodily action – and by the methodology that Du Châtelet develops and applies in order to address this problem.