Newton's Law of Inertia applies to which condition of flight?

• A. Balanced
• B. Unbalanced
• C. Steady
• D. Nonlinear

Answer: (A)

Newton's first law says a body stays at rest or continues in uniform motion unless a net external force acts on it. In flight this shows up when the forces are balanced—lift equals weight and thrust equals drag. With no net force, there’s no acceleration, so the aircraft keeps its current speed and direction. That steady state is inertia in action. If the forces were unbalanced, a net force would cause the aircraft to accelerate or decelerate, which isn’t inertia. Nonlinear doesn’t describe this force-balance condition. So the situation where inertia applies in flight is the balanced condition.