An airplane flies because its wings push down on the air
flowing past them, and in reaction, the air pushes up on the wings. When an
airplane is level or rising, the front edges of its wings ride higher than the
rear edges. The angle the wings make with the horizontal is called the angle of
attack. As the wings move through the air, this angle causes them to push air
flowing under them downward. A sleeper angle of attack will cause the wings to
push more air downward. The third law of motion voiced by English physicist
Isaac Newton states that every action produces an equal and opposite reaction.
In this case, the wings pushing air downward is the action, and the air pushing
the wings upward is the reaction. This causes lift, the upward force on the
plane, Lift is often explained using Bernoulli’s principle, which states that,
in some circumstances, a faster moving fluid(流体) (such as air)will have a lower
pressure than a slower moving fluid. The air on the top of an airplane wing is
at a lower pressure than the air underneath the wing, but this is an effect of
lift, not its cause. Lift is one of the four primary forces
acting upon an airplane. The others are weight, thrust, and drag. Weight is the
force that offsets lilt. because it acts in the opposite direction. The weight
of the airplane must be overcome by the lift produced by the wings, if an
airplane weighs 4.5 metric tons, then the lift produced by its wings must be
greater than 4.5 metric tons in order for the airplane to leave the ground.
Designing a wing that is powerful enough to lift an airplane off the ground, and
yet efficient enough to fly at high speeds over extremely long distances, is one
of the marvels of aircraft technology. In the last sentence "Designing a wing that is powerful enough to lift an airplane off the ground, and yet efficient enough to fly at high speeds over extremely long distances, is one of the marvels of aircraft technology.", what is the meaning of the word "marvel"