1. Which of the following statements best describes Newton's first law of motion? A. An object at rest tends to stay at rest unless acted upon by an external force. B. The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. C. For every action, there is an equal and opposite reaction. D. An object in motion will remain in motion at a constant velocity unless acted upon by an external force. Answer: D. An object in motion will remain in motion at a constant velocity unless acted upon by an external force. Rationale: This statement is the essence of Newton's first law, also known as the law of inertia. 2. According to the equation F = ma, what does "F" represent? A. Mass B. Acceleration