The phenomenon that describes the tendency for an object to resist changes in its state of motion is known as inertia. Defined by Newton's first law of motion, inertia indicates that an object will remain at rest or continue moving in a straight line unless acted upon by an external force. This property is foundational in physics, affecting how objects move and interact with one another. The concept of inertia explains why a moving vehicle requires a force to stop and why an object at rest remains stationary until disturbed.