Name this tendency of matter to continue moving in a straight line at a constant speed, or to stay at rest if it is at rest—in other words, to oppose changes in its motion.
Frames of reference that are not accelerating are named for this property; in them, no fictitious forces appear. This property necessitates the application of an external net force to counter its behavior. Newton's First Law of Motion is often called the law of this property, which is (*) proportional to, and thus often conflated with, mass. Name this tendency of matter to continue moving in a straight line at a constant speed, or to stay at rest if it is at rest—in other words, to oppose changes in its motion.
Frames of reference that are not accelerating are named for this property; in them, no fictitious forces appear.
{inertia} [do not accept "moment of inertia" or "rotational inertia"; accept {inertia}l reference frames]