Which law states that an object will continue moving at a constant velocity in a straight line if no net external force acts on it?

Which law states that an object will continue moving at a constant velocity in a straight line if no net external force acts on it?

• A. Newton's Second Law of Motion
• B. Newton's Third Law of Motion
• C. The Law of Gravity
• D. Newton's First Law of Motion

Answer: (D)

This is Newton's First Law, also known as the law of inertia. It says objects tend to keep doing what they are already doing unless something else starts pushing or pulling on them. If there’s no net external force acting on an object, the acceleration is zero, so its velocity stays constant. That means it would keep moving in a straight line at the same speed and direction unless a net force changes either its speed or its direction. Think of inertia as the resistance to changes in motion. Without a net force, there’s nothing to change the motion, so the object maintains its state. The other laws describe why motion changes when forces are present (the Second Law links net force to acceleration, the Third Law covers action-reaction pairs) or describe gravitational effects, which are about specific forces rather than the general rule about motion with no net force.

This is Newton's First Law, also known as the law of inertia. It says objects tend to keep doing what they are already doing unless something else starts pushing or pulling on them. If there’s no net external force acting on an object, the acceleration is zero, so its velocity stays constant. That means it would keep moving in a straight line at the same speed and direction unless a net force changes either its speed or its direction.

Think of inertia as the resistance to changes in motion. Without a net force, there’s nothing to change the motion, so the object maintains its state. The other laws describe why motion changes when forces are present (the Second Law links net force to acceleration, the Third Law covers action-reaction pairs) or describe gravitational effects, which are about specific forces rather than the general rule about motion with no net force.