Who first stated that an object in motion will remain in motion unless acted upon by an external force?

The statement that an object in motion will remain in motion unless acted upon by an external force is a fundamental principle in physics known as Newton's First Law of Motion. This law was first formulated by Sir Isaac Newton in the 17th century.

Newton's First Law emphasizes the concept of inertia, indicating that in the absence of a net force, an object's velocity will remain constant. This principle laid the groundwork for classical mechanics and provides a clear understanding of how forces affect the motion of objects.

While Galileo did make significant contributions to the study of motion and inertia, it was Newton who formally articulated this law and integrated it into his larger framework of physics. Other thinkers, such as Einstein and Aristotle, approached the concepts of motion and force differently, with Einstein focusing on relativity and Aristotle on a pre-scientific understanding of natural motion. Thus, Newton is the correct choice for the origin of this specific law.