  Euler was the central figure in turning the three laws of motion put forward by Newton in the Principia into Newtonian mechanics. These three laws, as Newton formulated them, apply to “point-masses,” a term Euler had put forward in his Mechanica of 1736. Most of the effort of eighteenth century mechanics was devoted to solving problems of the motion of rigid bodies, elastic strings and bodies, and fluids, all of which require principles beyond Newton's three laws. From the 1740s on this led to alternative approaches to formulating a general mechanics, employing such different principles as the conservation of vis viva, the principle of least action, and d'Alembert's principle. The “Newtonian” formulation of a general mechanics sprang from Euler's proposal in 1750 that Newton's second law, in an F=ma formulation that appears nowhere in the Principia, could be applied locally within bodies and fluids to yield differential equations for the motions of bodies, elastic and rigid, and fluids. During the 1750s Euler developed his equations for the motion of fluids, and in the 1760s, his equations of rigid-body motion. What we call Newtonian mechanics was accordingly something for which Euler was more responsible than Newton.