Which concept explains that a rotor blade pushing air downward experiences an equal and opposite reaction on the blade?

Which concept explains that a rotor blade pushing air downward experiences an equal and opposite reaction on the blade?

• A. Gravity
• B. Action/Reaction
• C. Inertia
• D. Momentum

Answer: (B)

When a rotor blade pushes air downward, it exerts a force on the air. In return, the air pushes back on the blade with an equal and opposite force. This is Newton's third law in action—the action of pushing air downward and the reaction of the air pushing on the blade. That reaction force is what provides the lift component on the blade, balancing weight and enabling flight. Gravity, inertia, and momentum describe related ideas, but they don’t capture this direct, pairwise force exchange between blade and air.

When a rotor blade pushes air downward, it exerts a force on the air. In return, the air pushes back on the blade with an equal and opposite force. This is Newton's third law in action—the action of pushing air downward and the reaction of the air pushing on the blade. That reaction force is what provides the lift component on the blade, balancing weight and enabling flight. Gravity, inertia, and momentum describe related ideas, but they don’t capture this direct, pairwise force exchange between blade and air.