In physics, what does inertia refer to?

Inertia refers to the tendency of an object to resist changes in its state of motion, which aligns precisely with the characteristics of mass and how it interacts with forces. An object at rest tends to stay at rest, and an object in motion continues to move at a constant velocity unless acted upon by an external force. This fundamental concept is rooted in Newton's First Law of Motion, which describes how the presence or absence of force influences the motion of objects. The more mass an object has, the greater its inertia, making it harder to change its motion. This principle is crucial for understanding various phenomena in physics, from everyday motion to complex mechanical interactions.

Other options refer to different principles in physics: gravity relates to the attractive force between masses, net force describes the overall force resulting from combining all acting forces, and equilibrium in force distribution pertains to balanced forces in a static situation. However, these concepts do not encapsulate the essence of inertia.