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[Phys-L] the plane truth



In teaching about fluids, I was discussing that airplanes fly because of
Bernoulli's equation (principle). The shape of the wing allows air going
over the wing to travel faster than that going under the wing. Then the
pressure under the wing is higher than that above, providing "lift." Here
are my two issues with this:

1) Exactly how does the air travel faster over the wing? If the plane is
going at a constant speed, then shouldn't the speed of air relative to the
wings be the same? I've heard that the air at the front of the wing must
meet again at the back of the wing. But what would happen if the plane
were to somehow move through a more dense fluid, say, water? Would the
same thing ("lift") happen?

2) I know that some planes can fly upside down. How can this be understood
in terms of lift and Bernoulli's equation?

Can anybody offer insights into these issues?
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