`  :::Doug, I disagree that we must spell out what body of air it's true for  at least in the introductory section.  I believe it is possible to be intentionally vague without prompting the question of ``but which body of air?`` in most reader's minds.  Something along the lines of:  ::::In accordance with Newton's second law F=ma, some of the air surrounding the airfoil is accelerated downward.  The rate at which downward momentum is imparted to a portion of the air is equal to the lift. (See ``Momentum balance in lifting flows`` for details)  :::It's not a question of length - the issue is whether or not it is a distraction for the reader  and I think a detailed description of control volume analysis at this stage of the article would be a distraction for most readers. The more detailed it is, the more likely we are to lose our audience. I'd prefer to keep the intro sections simple. Those who want more details can follow the link.    `