Inertia is the resistance of an object has to a change in its state of motion.
Newton's conception of inertia stood in direct opposition to more popular conceptions about motion. The dominant thought prior to Newton's day was that it was the natural tendency of objects to come to a rest position.
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 his first law in his Philosophiæ Naturalis Principia Mathematica.
