# What causes lift in aerofoil: Bernouli's principle or Newton's third law? [duplicate]

Reading materials online, I observe some explanation based on Bernoulli's principle, quoting the difference of air pressure above/below and difference of speed of airflow. While some say's Bernoulli's principle works only in special conditions (laminar, non-viscous, non-compressible, streamline, etc.) and the correct working is based on Newton's third law whereby, the airfoil pushes the stream downward and experiences lift upwards.

Bernouli's principle is also said to not work for symmetrical aerofoils and inverted aerofoil.

What is the final verdict of what causes lift?

• Could you share your sources for the statements that Bernouli's principle only works in special conditions?
– GdD
May 20, 2020 at 7:31
• @GdD - khanacademy.org/science/physics/fluids/fluid-dynamics/a/… It is pretty standard thing that bernouli's principle is valid only for streamline, non-turbulent, non-viscous, incompressible flows. May 20, 2020 at 7:58
• @RajArjit, actually, Bernoulli's equation is just formulation of conservation of energy for adiabatic fluid flows, and often given for incompressible flows only (then you don't need to add the equation for adiabatic compression), and as such is always valid. May 20, 2020 at 8:26
• … of course with turbulent flow you have to take the $v$ in the Bernoulli's equation to mean the average magnitude of velocity of the particles, which is higher than their average forward velocity. But that does not make Bernoulli's equation invalid, just more complicated. May 20, 2020 at 8:52