According to Newton's first law, what happens to an object at rest unless acted on by an outside force?

According to Newton's first law of motion, an object at rest will remain at rest unless acted upon by an external force. This principle emphasizes the concept of inertia, which is the tendency of objects to maintain their state of motion, whether that be at rest or moving at a constant velocity. In this case, if no external force influences the object, its state of rest is maintained.

Inertia explains why a stationary object won't start moving on its own; it requires a force to change that state. Therefore, the answer provided reflects a fundamental principle of physics regarding motion and forces.

The other choices do not properly encapsulate this principle. An object at rest does not spontaneously accelerate, gain weight, or change direction without some form of external influence. These scenarios involve forces acting on the object, which is contrary to the specified conditions in the question.