What is inertia?

Inertia is defined as the tendency of an object to continue in its current state of motion, whether that is at rest or moving at a constant velocity. This principle stems from Newton's First Law of Motion, which states that an object will not change its motion unless acted upon by an external force. Essentially, if no net force is acting on an object, it will not change its state; it will keep moving in a straight line or remain stationary.

This concept is fundamental in understanding motion and forces, as it explains why objects resist changes to their motion. For example, if a car is traveling at a constant speed and suddenly encounters a brake, the inertia of the car would cause it to want to keep moving forward despite the application of braking force.

The other choices do not accurately represent the concept of inertia. The ability to change direction is more related to an object's responsiveness to forces acting upon it, rather than its inertia. The force acting on an object describes the influence causing that object to accelerate, rather than its tendency to maintain its state of motion. Finally, speed refers to how fast an object is moving, not its resistance to changing that motion, which is what inertia is fundamentally about.