“Bernoulli's principle, involving pressure differences, and Newton's third law, involving reaction forces, are two descriptions of the same underlying physical mechanism.”

There are two classes of popular explanations of lift: one based on Bernoulli’s equation relating pressure to velocity and another based on Newton’s second and third laws applied to the flow momentum deflected downward [2]. Here, a brief review of the popular explanations is given to show why they are incomplete.

So both “Bernoulli” and “Newton” are correct. Integrating the effects of either the pressure or the velocity determines the aerodynamic force on an object. … Newton’s laws of motion are statements concerning the conservation of momentum. Bernoulli’s equation is derived by considering conservation of energy. So both of these equations are satisfied in the generation of lift; both are correct.

According to Dr. Jean-Jacques Chattot, professor of Mechanical and Aeronautical Engineering and director of the Center for Computational Fluid Dynamics at the University of California-Davis, the descriptions of lift advocated by Newton and Bernoulli “are actually the same thing, just from two different perspectives.” … Not surprisingly, Bernoulli’s equation is actually derived from Newton’s laws. Bernoulli and Newton each correctly describe lift, but use divergent methods.

Newton's laws of motion are statements concerning the conservation of momentum. Bernoulli's equation is derived by considering conservation of energy. So both of these equations are satisfied in the generation of lift; both are correct.

So both "Bernoulli" and "Newton" are correct. Integrating the effects of either the pressure or the velocity determines the aerodynamic force on an object. … Newton's laws of motion are statements concerning the conservation of momentum. Bernoulli's equation is derived by considering conservation of energy. So both of these equations are satisfied in the generation of lift; both are correct.

So both "Bernoulli" and "Newton" are correct. Integrating the effects of either the pressure or the velocity determines the aerodynamic force on an object. … Newton's laws of motion are statements concerning the conservation of momentum. Bernoulli's equation is derived by considering conservation of energy. So both of these equations are satisfied in the generation of lift; both are correct.

According to Newton’s third law of motion, the action of the wings moving through the air creates lift. In its simplest explanation, lift is a product of wing shape and the outcome of the total pressure on the bottom of the wing being greater than the total pressure on top of the wing.

The experimentally observed Bernoulli’s principle originates from the Euler equation which is the application of Newton’s 2nd law for inviscid fluid systems. … There is no contradiction! While the Newtonian laws of classical mechanics cannot be violated, Bernoulli’s energy and linear momentum principle offers easier and more natural description and insights of the pressure and velocity changes over the wing or blade.

Almost all elementary textbook explanations of the theory of flight rely heavily on Bernoulli’s principle and the fact that air travels faster over a wing than below it. In recent years the inadequacies and, indeed, fallacies in this explanation have been exposed (see Babinsky’s excellent article in 2003 Phys. Educ. 38 497–503) and it is now appreciated that it is possible to provide a much simpler explanation in terms of Newton’s laws.

The net fluid force is generated by the pressure acting over the entire surface of a closed body. The pressure varies around a body in a moving fluid because it is related to the fluid momentum (mass times velocity). The velocity varies around the body because of the flow deflection described above.

One of the most popular incorrect theories states that the upper surface of an airfoil is shaped longer than the lower surface so that the flow over the top travels faster to reach the trailing edge at the same time. The higher velocity produces lower pressure according to Bernoulli’s equation and the difference in pressure produces the lift. … Lift occurs when a flow of gas is turned by a solid object. The flow is turned in one direction, and the lift is generated in the opposite direction, according to Newton’s Third Law of action and reaction.

Both Bernoulli's law and Newton's laws describe lift production correctly.

One popular explanation for how this happens is based on Bernoulli's principle, which describes the relationship between the velocity and pressure exerted by a fluid in motion. … An alternative, perhaps even complementary, explanation calls on Newton's third law of motion: for every action, there is an equal and opposite reaction.

Denker says, "There is only one lift-producing process. Each of the explanations itemized above concentrates on a different aspect of this one process. The wing produces circulation in proportion to its angle of attack (and its airspeed). This circulation means the air above the wing is moving faster. This in turn produces low pressure in accordance with Bernoulli's principle. The low pressure pulls up on the wing and pulls down on the air in accordance with all of Newton's laws."

Which is best for describing how aircraft get the needed lift to fly? Bernoulli's equation or Newton's laws and conservation of momentum? This has been an extremely active debate among those who love flying and are involved in the field. If the question is "Which is physically correct?" then the answer is clear -- both are correct. Both are based on valid principles of physics.

The relationship is thus a mutual, or reciprocal, interaction: Air flow changes speed or direction in response to pressure differences, and the pressure differences are sustained by the air's resistance to changing speed or direction. … Sustaining the pressure difference that exerts the lift force on the airfoil surfaces requires sustaining a pattern of non-uniform pressure in a wide area around the airfoil. This requires maintaining pressure differences in both the vertical and horizontal directions, and thus requires both downward turning of the flow and changes in flow speed according to Bernoulli's principle.

The pressure differences and the changes in flow direction and speed sustain each other in a mutual interaction.

So what explains lift? Lift is explained in part by the Bernoulli Principle, the Coanda Effect, and Newton’s Third Law of Motion.

Because the air moving over the top of a curved wing tends to go faster than the air under the wing, there is also less pressure at the top of curved wings, and more pressure below the wings. This principle of fast moving air having less pressure is known as Bernoulli’s Principle, and also helps generate lift (Fig. 3).

For a moving flow, the pressure will vary from point to point because the velocity varies from point to point. For some simple flow problems, we can determine the pressure distribution (and the net force) if we know the velocity distribution by using Bernoulli’s equation.

The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation.

The pressure on top of the wing is therefore reduced, creating a net upward force or lift. (Wings can also gain lift by pushing air downward, utilizing the conservation of momentum principle. The deflected air molecules result in an upward force on the wing — Newton’s third law.)

The pressure on top of the wing is therefore reduced, creating a net upward force or lift. (Wings can also gain lift by pushing air downward, utilizing the conservation of momentum principle. The deflected air molecules result in an upward force on the wing — Newton’s third law.)

It must be emphasized that you do not get to choose Bernoulli's principle "instead of" Newton's laws or vice versa. Bernoulli's principle is a consequence of Newton's laws. … There is only one lift-producing process. Each of the explanations itemized above concentrates on a different aspect of this one process. The wing produces circulation in proportion to its angle of attack (and its airspeed). This circulation means the air above the wing is moving faster. This in turn produces low pressure in accordance with Bernoulli's principle. The low pressure pulls up on the wing and pulls down on the air in accordance with all of Newton's laws.

According to Bernoulli’s equation, if we follow a small volume of fluid along its path, various quantities in the sum may change, but the total remains constant. Bernoulli’s equation is, in fact, just a convenient statement of conservation of energy for an incompressible fluid in the absence of friction.

Bernoulli's principle can also be derived directly from Isaac Newton's second law of motion. … In the above derivation, no external work–energy principle is invoked. Rather, Bernoulli's principle was derived by a simple manipulation of Newton's second law.

The Bernoulli equation can be derived by integrating Newton’s 2nd law along a streamline with gravitational and pressure forces as the only forces acting on a fluid element.

Recall that Newton’s 2 nd Law states that the sum of all forces in a particular direction is equal to the time rate of change of momentum.

That’s why an explanation of lift requires Bernoulli’s Principle and Newton’s Third Law to be accurate and complete.

We can also derive Bernoulli’s Equation using the Linear Momentum Equations and Conservation of Mass applied to a di↵erential control volume as shown in Figure 5.32.

Bernoulli's principle can also be derived directly from Isaac Newton's second law of motion. … In the above derivation, no external work–energy principle is invoked. Rather, Bernoulli's principle was derived by a simple manipulation of Newton's second law.

Is Bernoulli's principle or Newton's third law responsible for it? or both the effects? … Is there any fundamental law of physics that justify the lift rather than this fluid mechanics-based explanation? Yes – Newton's third law of motion. You can see that the airfoil deflects the flow as shown in Fig 12, or it pushes the flow downward. So, according to Newton's third law, the air also should push the airfoil in opposite direction with equal magnitude. This results in lift.

Bernoulli's principle states that for ideal fluids (like water in the example above), as the speed of the fluid increases, its pressure decreases due to the conservation of energy.