sentence2_structure: Newton's second law of motion<>is<>more than a definition$$$it<>is<>a relationship among acceleration, force, and mass
sentence1: Newton's Second Law of Motion states that the force or action of a rocket engine is directly proportional to the mass expelled times its acceleration.
sentence2: Newton’s second law of motion is more than a definition; it is a relationship among acceleration, force, and mass.
question: Newton’s second law of what is more than a definition; it is a relationship among acceleration, force, and mass?