What is defined as the tendency of objects to resist changes in motion?

The correct choice is based on the definition of inertia, which is a fundamental property of matter that describes an object's resistance to changes in its state of motion. Inertia is directly related to an object's mass; the greater the mass of an object, the greater its inertia and the more force that is required to change its velocity, whether that means speeding up, slowing down, or changing direction.

Kinetic energy relates to the energy of an object in motion, which doesn't address the resistance to motion itself. Mass is a measure of the amount of matter in an object and contributes to inertia, but it doesn't define the concept on its own. Friction refers to the resistive force that occurs when two surfaces interact, affecting motion but not fundamentally defining the property of inertia.

Understanding inertia is crucial as it plays a significant role in Newton's first law of motion, which states that an object at rest stays at rest, and an object in motion continues in motion with the same speed and in the same direction unless acted upon by a net external force. Thus, inertia is essential in evaluating how objects will behave when forces are applied to them.