What is Newton's First Law of Motion?

Newton's First Law of Motion states that an object will remain at rest, or in uniform motion in a straight line, unless acted upon by an external force. While choice B partially captures this principle by addressing an object in motion, it refers specifically to unbalanced forces, which is a correct interpretation of how motion persists when no opposing force is present.

The crux of the law emphasizes the concept of inertia, which is the natural tendency of objects to resist changes in their state of motion. This means that an object at rest will not start moving unless a force pushes or pulls it, and an object in motion will not stop or change direction unless a force acts upon it. The focus on unbalanced forces in choice B highlights that for motion to change, a force must disrupt that inertia, which is indeed a critical aspect of the law.

Options that suggest different interpretations, such as the incorrect associations of equal and opposite forces or the relative nature of motion, do not accurately define Newton's First Law, thereby clarifying why the provided answer is the most aligned with the law’s fundamental principles.