This is a quote I read and im having problems understanding it:

"Lift is produced by the changing direction of the flow around a wing. The change of direction results in a change of velocity (even if there is no speed change, just as seen in uniform circular motion), which is an acceleration. To change the direction of the flow therefore requires that a force be applied to the fluid; lift is simply the reaction force of the fluid acting on the wing."

The part I do not understand is that lift is the reaction force of the fluid on the wing, should it not be the other way arround?

rcgldr
Homework Helper
The part I do not understand is that lift is the reaction force of the fluid on the wing, should it not be the other way arround?
If it wasn't for gravity, then you'd have a pair of equal and opposing reaction forces, the air accelerated in one direction, the aircraft accelerated in the other. Since the aircraft has a much higher density, most of the accleration will occur with the air.

With the presence of gravity to generate a downforce on an aircraft, and while in level flight, the air craft isn't accelerating upwards, but the air is accelerating downwards (lift) (also a bit forwards (drag) and/or backwards (thrust)).