Final answer:
Lift and drag are the forces acting on a rotor blade of a helicopter hovering in still air. Lift is created by the rotor blades pushing air downwards and experiencing an upward reaction force, and drag is the resistance encountered as the blades move through the air.
Step-by-step explanation:
The forces that act on a rotor blade hovering in still air are lift and drag. When a helicopter's rotor blades spin, they push air downwards. This action has an equal and opposite reaction according to Newton's Third Law, which means the air pushes back on the blades creating lift, allowing the helicopter to hover. Additionally, as the blades slice through the air, they encounter air resistance, which is known as drag. Both of these forces (lift and drag) act on a rotor blade in a helicopter hovering in still air.
Helicopters create lift by pushing air down, thereby experiencing an upward reaction force. The air pushes upward on the helicopter, creating lift, which is an external force acting on it. Simultaneously, the blades experience drag, another external force, which resists the motion through the air. This is similar to how other flying objects like birds and airplanes operate; they exert force on the air in the opposite direction to achieve lift and propulsion.