✔ 最佳答案
This is only an assumption that air particles on top and bottom of a wing meet at the same time. Unfortunately, this assumption is not always true in practice especially when the plane is flying at high speed. It is only true when the wings are moving at low speed, i.e. at condition of "stream line flow".
You could imagine that the wing is moving in still air. In other words, the air is NOT moving. It is only the wing that moves. Hence, two air particles orginally facing each other before the wing arrives should again be facing each other after the wing has passed, simply because the air (and hence its particles) is not moving at all.
It is well known that Bernoulli Principle cannot fully explain the lifting force on a wing (although only such principle is taught in high school physics). There are many flaws in it. If the force arising from Bernoulli effect is the only force developed to lift an aircraft, then the aircraft should not be able to fly upside down when its wings are inverted. In fact, many aircrafts can fly upside down.
You may wish to read the following web-pages, which give a good and simple explanation to the lifting force on a wing"
http://science.howstuffworks.com/airplane5.htm
http://science.howstuffworks.com/airplane6.htm
http://science.howstuffworks.com/airplane7.htm
http://science.howstuffworks.com/airplane8.htm