What best defines inertia in physics?

Inertia is fundamentally defined as the tendency of an object to maintain its state of rest or uniform motion unless acted upon by an external force. This concept is rooted in Newton's First Law of Motion, which states that an object will not change its velocity unless a net force is applied to it. In other words, if an object is at rest, it will stay at rest, and if it is moving, it will continue to move at a constant speed in a straight line, reflecting its inherent resistance to changes in motion. This attribute of inertia is critical in understanding how forces affect objects in motion, making it a foundational principle in both physics and aeromedical contexts.

The other definitions provided do not capture the essence of inertia. While speed, force, and acceleration are related concepts in physics, they do not define inertia itself. Inertia specifically pertains to the object's resistance to changes in its state of motion, distinguishing it from these other physical quantities.