Philosophiæ Naturalis Principia Mathematica
Inertia comes from the Latin word, "iners", meaning idle, sluggish. Inertia is one of the primary manifestations of mass, which is a quantitative property of physical systems. Isaac Newton defined inertia as a force, before his first law in the monumental "Philosophiæ Naturalis Principia Mathematica". There, one reads: