Air velocity & pressure

Air has mass and moving air has momentum. If the air parcel follows a curved path, there must be a net force on it, as required by Newton's laws.

Using the law that total energy cannot change, whenever a given parcel of air increases its velocity, it must decrease its pressure, and vice versa.
This relationship is called Bernoulli's principle.

At high angles of attack a wing is extremely effective at speeding up the air above the wing and retarding the air below the wing. The maximum local velocity above the wing can be more than twice the free-stream velocity. This creates a negative pressure of more than 3 times  the positive pressure under the wing.