What does the term 'inertia' refer to in physics?

In physics, inertia refers to the property of an object that causes it to resist any change in its state of motion. This means that an object at rest will remain at rest, and an object in motion will continue to move at a constant velocity in a straight line unless acted upon by an external force. This concept, rooted in Newton's First Law of Motion, highlights how mass plays a critical role in determining how much an object will resist changes to its speed or direction. Inertia is often associated with mass; the greater the mass of an object, the greater its inertia and the more force will be required to change its state of motion. Understanding inertia is essential in mechanics, as it helps explain various physical phenomena such as why a heavier object requires more force to accelerate than a lighter one.