Final answer:
Newton's first law of motion states that an object at rest remains at rest and an object in motion maintains its velocity unless it is acted upon by a net external force. This is also known as the law of inertia and describes the resistance of any physical object to any change in its state of motion.
Step-by-step explanation:
Newton's first law of motion, commonly known as the law of inertia, essentially states that an object at rest will stay at rest, and an object in motion will stay in motion with a constant velocity, which means at a constant speed and in a straight line, unless acted upon by a net external force. This concept suggests that there is a natural tendency of objects to keep on doing what they're doing. All objects resist changes in their state of motion, but they will change their motion if a net force acts upon them.
Therefore, the correct statement that represents Newton's first law of motion is: objects at rest or in motion, will stay at rest or in motion, unless acted on by an unbalanced force. This implies that an external force is necessary to change the velocity (either the magnitude which is speed or the direction) of the object. Friction is an example of a net external force that can cause an object that is moving to slow down and eventually stop.