The physical property that measures an object's resistance to motion is known as inertia. Inertia is closely related to an object's mass: the more massive an object is, the greater its inertia, meaning it requires more force to change its state of motion, whether to start moving, stop, or change direction. This property is a fundamental concept in Newtonian mechanics, reflecting how physical bodies respond to applied forces. Understanding inertia is essential in various fields, such as physics, engineering, and mechanics, as it helps predict how objects behave in motion or at rest under different conditions.