Which law of motion would describe an object staying still until acted upon?

The principle that describes an object remaining at rest until an external force acts upon it is captured by Newton's First Law of Motion. This law, often referred to as the law of inertia, states that an object at rest will stay at rest, and an object in motion will remain in motion at a constant velocity, unless acted upon by a net external force.

This concept underscores the idea that if there is no force to change its state, whether that state is rest or uniform motion, the object will not change its position or velocity. It emphasizes the fundamental concept of inertia, which suggests that all objects resist changes in their state of motion.

The other laws mentioned do not apply to this scenario. Newton's Second Law pertains to the relationship between force, mass, and acceleration, focusing on how forces cause changes in motion, rather than maintaining a state of rest. Newton's Third Law deals with action and reaction forces, indicating that for every action, there is an equal and opposite reaction, which does not directly address the concept of an object remaining still. Meanwhile, the Law of Conservation of Energy involves the transformation of energy rather than the motion of objects in relation to forces acting on them.