Plane / Planes / Aircraft / Aeroplane / Airplane appreciation

ARTHUR: Oh, yes. About that. Um, I wanted to ask you something, Skipper. Mum was telling me this morning that planes fly because they’ve got wings.
DOUGLAS: Is there anything that woman doesn’t know?
ARTHUR: But she didn’t really explain – why do wings lift us up?
DOUGLAS: Ah, well. Essentially …
MARTIN: Uh, Douglas, he asked me. Listen carefully, Arthur. The wing is curved on top but flat on the bottom. When it meets the air, it splits it in two. The air that goes over the top has further to go, so it has to go faster to keep up with the air underneath. That reduces the pressure above the wing, giving us lift.
ARTHUR: Ah, fantastic! Thanks, Skipper! I totally get it now.
MARTIN: You’re welcome.
ARTHUR: Except … why does it have to?
MARTIN: Why does what what?
ARTHUR: Why does the air on the top have to keep up with the air on the bottom? Why don’t they just split up?
(Everyone stops walking. There’s a long pause.)
DOUGLAS: … For the sake of the kids?

...

DOUGLAS (talking over him): Arthur, you were asking why the air over the wing has to keep up with the air underneath.
ARTHUR: Ooh, yes. Do you know?
DOUGLAS: Indeed I do. Attend: the air is not passing over the wing; the wing is passing through the air, so the curved upper side stretches the air forced over it apart, reducing pressure, producing lift. The lift pushes up; the weight pushes down – so as long as the lift is more than the weight, up we go. And that, my friend, is how an aeroplane flies.
ARTHUR: Got it! Right, yes! Cracking! I completely get it now.
DOUGLAS: Good. You see, it’s actually quite easy to grasp when it’s explained properly by someone who understands …
ARTHUR: So that’s why planes can’t fly upside down.
DOUGLAS: Er, yes they can.
ARTHUR: Can they?
DOUGLAS: Well, of course they can. Haven’t you seen the Red Arrows?
ARTHUR: But … doesn’t that mean the curved side of the wing is on the bottom, so the lift is pushing down as well as the weight? How does that work?