tisdag 18 september 2012

Hyperphysics: Bernoulli of Newton's Law for Lift?

The explanation of the generation of lift of a wing on the educational site Hyperphysics gives evidence of the depth of the crisis of present aerodynamics education:
  • 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 Bernoulli equation is simply a statement of the principle of conservation of energy in fluids. Conservation of momentum and Newton's 3rd law are equally valid as foundation principles of nature - we do not see them violated. 
  • This physical validity will undoubtedly not quell the debate, and this treatment will not settle it. But perhaps it can at least indicate the lines of the discussion.
We see two explanations of the generation of lift being presented, both expressing valid physics, but both being trivial as being self-evident: lift by lower pressure above (Bernoulli) or lift as reaction (Newton). This is true but carries no interesting information like any triviality.

Each proponent of an explanation can rightly accuse the other for presenting a triviality and so the proponents cannot meet, although they share equally valid trivial arguments.

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