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Do you agree that the net momentum transfered to the Earth by the
air molecules is equal and opposite to the net momentum transferred to the wing by the air molecules? Yes. Do you agree, therefor that there is no net momentum transfered to the air? Overall, yes. Similarly, there is no net momentum transferred to the basketball when it is being used to support a (very fast) dribbler. But that is not to say that there is no momentum transfer. The basketball certainly moves around. I do agree that the net overall is zero. The air does not pile up permanently. At which ponit the Earth throws the air molecule back up so that the net momemtum transferred to the air molecule is zero (averaged over the entire atmosphere) Yes. [it hits the wing on the way up] Which again transferes an equal and opposite momentum to the molecule which again is transferrred to the Earth leaving no net transfer of momentum to the air. Yes. Overall, there is no net (or "permanent") transfer of momentum to the air. The air is an intermediary, keeping the wing and the earth apart. There is certainly =energy= transfer to the air (mv^2/2), and there is a lot of momentum transfer =back=and=forth= with the air, but I will agree that the net is zero. The air is sort of a catalyst - ending up unchanged as it transfers momentum to the earth and then transfers it back from the earth to the wing. So.. after all that, I think we are in agreement - there is no =net= (permanent) vertical momentum transfer to the air, but there is locally momentum transferred to the air, which carries it to the earth and uses it to neutralize the momentum the earth has acquired being attracted to the plane, in doing so it acquires momentum in the opposite direction and transfers it to the wing, ending the cycle and leavint the air ready to act as momentum messenger again. It carries momentum messages both ways, they (overall) cancel out, but do keep the earth and the wing separated. === In addition, the wing is throwing air forwards, due to its AOA and its own forward motion. (this acts as drag, counteracted by the engine). The air thrown forwards increases the pressure in front of the wing, that plus the air thrown down makes the air pressure in front of and below the wing higher, causing the air to rise in front of the wing. This rising air helps lift the wing; this is the source of induced drag. Some of the rising air spills around the wingtips, causing vortices. The vortices are not the cause of lift, they are an inescapable side effect of lift. Concur? Jose -- Money: what you need when you run out of brains. for Email, make the obvious change in the address. |
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