What does Newton's 1st Law describe about objects in motion?

Newton's 1st Law of Motion, often referred to as the law of inertia, states that an object will remain at rest or move in a straight line at a constant speed unless acted upon by a net external force. This principle highlights the concept of inertia, which is the tendency of an object to resist changes in its state of motion. Therefore, an object that is already in motion will continue moving at a constant velocity unless a force causes it to change that motion.

This means that if there’s no net force acting on a moving object, it has no reason to stop or alter its direction, thereby illustrating the persistence of its state of motion. The law provides a foundational understanding of how motion works in the absence of forces, and why objects do not spontaneously change their state of motion. This is why the option stating that they will stay in motion unless acted upon by a force accurately captures the essence of Newton's 1st Law.