What is Newton's first law of motion?

Newton's first law of motion states that an object at rest will remain at rest, and an object in motion will continue moving at a constant velocity in a straight line 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.

The correct choice emphasizes that unless an external force intervenes, whether to stop, accelerate, or change the direction of the object, its state of motion will not change. This law fundamentally describes how motion does not require a force to maintain it; rather, a force is necessary only to change that motion.

In contrast, the other statements deviate from this principle. The option discussing forces causing objects to move in a straight line suggests a misunderstanding of the role of forces, which instead act to change motion, not to sustain it. The assertion about energy reflects a separate principle known as the law of conservation of energy, rather than any principle related to motion. Lastly, the idea that objects require constant force to remain in motion misinterprets the nature of inertia as prescribed in Newton's first law. In fact, continuous motion does not require constant force, highlighting the distinction between motion and the forces that might alter that motion