Aerodynamics

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Aerodynamics, branch of fluid mechanics that deals with the motion of air and other gaseous fluids, and with the forces acting on bodies in motion relative to such fluids. The motion of an airplane through the air, the wind forces exerted on a structure, and the operation of a windmill are all examples of aerodynamic action such as airplanes.

One of the fundamental forces studied in aerodynamics is lift, or the force that keeps an airplane in the air. Airplanes fly because they push air down. The leading edge of an airplane wing is slightly higher than the trailing edge when the plane is maintaining altitude. As the wing moves through the air, it deflects the air that flows underneath it downward. Air flowing over the top of the wing follows the surface of the wing and is also deflected downward. The third law of motion formulated by English physicist Sir Isaac Newton states that every action causes an equal and opposite reaction (see Newton’s Third Law of Motion). As the wing pushes the air down, the air pushes the wing up. Lift is also often explained using Bernoulli’s principle, which relates an increase in the velocity of a flow of fluid (such as air) to a decrease in pressure and vice versa. The pressure on the upper side of an airplane wing is lower than that on the lower side, and many engineers use equations derived from Bernoulli’s principle to design aircraft.

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