Which statement describes the state where the sum of all forces equals zero, resulting in no acceleration?

• A. Equilibrium
• B. Acceleration
• C. Velocity
• D. Momentum

Answer: (A)

When the sum of all forces is zero, there is no net force acting on the object. Newton’s second law tells us that acceleration equals net force divided by mass, so with zero net force the acceleration is zero. That means the object's velocity doesn’t change—it can be at rest or moving at a constant speed in a straight line. This condition is called equilibrium. In flight, for example, steady level flight is an equilibrium state where lift balances weight and thrust balances drag, producing no net force and no change in speed or altitude. The other concepts describe motion or momentum themselves, not the balance of forces that yields no acceleration.