Inertia in physics is the property of an object that resists changes to its state of motion. This means that an object at rest will remain at rest, and an object in motion will continue moving at a constant velocity in a straight line unless acted upon by an external force. Inertia is directly related to an object's mass—the greater the mass, the greater the inertia, and the more force required to alter its motion. This concept is a fundamental principle in Newton's First Law of Motion, often re