91Ó°ÊÓ

The equilibrium state is that state of the body when no net force acts on the body. In this state, there is no change in shape, size, or motion of the body despite the action of multiple forces.

Four forces act on the airplane while flying in the air, first is thrust due to the engines which produce an acceleration in forward direction; second, the drag force on the plane in the direction opposite to the thrust; third, the gravitational force acting downward, and the last, lift in the upward direction due to the wings.

The plane moves with constant velocity in smooth air (say at 800 km/h), and if it neither ascends nor descends, you could conclude that all the forces are balanced. And therefore, the airplane is in equilibrium. As a result, you don’t feel any sensation of motion.