What does inertia refer to in physics?

Inertia is fundamentally defined as the property of an object that quantifies its resistance to changes in its state of motion, which includes changes in speed or direction. This concept is tightly linked to Newton's First Law of Motion, which states that an object at rest will remain at rest, and an object in motion will continue to move at a constant velocity unless acted upon by an external force. Essentially, the greater the mass of an object, the greater its inertia, making it more challenging to alter its motion.

Understanding inertia helps explain why heavy objects are harder to push or stop compared to lighter ones. This characteristic is crucial in various applications in physics, such as understanding motion, designing safety mechanisms in vehicles, and predicting the behavior of objects in gravitational fields. The concept of inertia is a foundational principle in mechanics and is vital for analyzing motion in various physical scenarios.