Which law states that an object in motion tends to stay in motion unless acted upon by an outside force?

The statement describes Newton's first law of motion, which articulates the principle of inertia. This law asserts that an object will maintain its state of rest or uniform motion in a straight line unless compelled to change that state by an external force. This concept highlights the natural tendency of objects to resist changes in their motion, emphasizing the role of external forces in altering that motion.

In practical terms, when no net external force acts on an object, its velocity remains constant. For instance, if a ball is rolling on a surface and there are no additional forces (like friction or a push) acting upon it, it will not stop or change direction; it will continue to roll indefinitely.

Other choices refer to different principles in physics. Newton's second law relates to the acceleration of an object in relation to the net force applied and its mass. Newton's third law states that for every action, there is an equal and opposite reaction, which focuses on the interactions between two objects. The law of universal gravitation describes the attractive force between two masses but does not pertain to the concept of inertia or the motion of an individual object in isolation.