Why does wind velocity increase over a wing?

Also I have a bit of a paradox, people explain lift by saying there is a lower pressure region on the top of the airfoil and a higher pressure region on the lower airfoil. Then, they explain that there is a low pressure region due to the increased velocity of air (Bernoulli's).

They also explain that the velocity of air increases due to the low pressure region, surely one has to induce one or the other, or neither would happen? From where the extra energy is provided for kinetic energy of wind to increase?

  • $\begingroup$ Wing moves and experiences air drag, so apply Newton's 3rd Law of Motion for air in contact with the wing $\endgroup$
    – Garvit
    Apr 15, 2021 at 11:56
  • $\begingroup$ Bernoulli's principle isn't a statement about cause-and-effect. It's just a relationship between pressure and velocity. It's a valid relationship, but like you said, it can't explain by itself why air flows faster over the top of a wing. To explain that, we need more inputs. The only real explanations I've seen involve either computer simulations or nontrivial calculations (or both). The underlying principles are relatively simple, but their implications are non-intuitive. Were you hoping for an intuitive answer? $\endgroup$ Apr 15, 2021 at 13:07
  • $\begingroup$ Don't listen to "most people". A wrong explanation is rampant out there, having to do with air having to flow different distances. I could try to give you a correct explanation, but this guy has by far the best explanation. He actually knows what he's talking about. $\endgroup$ Apr 15, 2021 at 16:59
  • $\begingroup$ @ChiralAnomaly ,well put. The only other worthy explanations I have seen is 1. the air flows faster as the atmospheric pressure above the wing acts like a "wall" and therefore due to the law of mass flow rate its velocity has to be increased (I'm prettier sure this is wrong) 2. The air due to the kutta condition experiences a circulation effect which accerlates the air molecules (however I really don't understand these). Are either of these right? $\endgroup$
    – 3000 IQ
    Apr 16, 2021 at 19:19
  • $\begingroup$ @Guy Maybe I have the bar set too high, but I wouldn't be satisfied with a proposed qualitative explanation unless it could be turned into a quantitative one. I don't know how to do that with the mass-flow argument. Maybe it can be done, but I don't know how. The faster-flow-over-top property can be derived by considering a 2d flow around a cylinder and then applying a conformal transform that respects the kutta condition (you alluded to this in #2), but that approach assumes a steady state, so the distinction between cause and effect is lost, and it's still very mathematical. $\endgroup$ Apr 16, 2021 at 19:43


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