Birds and airplanes fly even
though they are heavier than air. This is accomplished
because of aerodynamics. Aerodynamics examines the forces of
lift, thrust, weight, and drag. These four forces affect
every surface that moves through the air. A bird is
aerodynamically designed. Its curved, feathered wings create
lift. Its streamlined shape allows it to move through
the air with very little resistance.
Engineers who study
aerodynamics, try to design airplanes the same way. They
create a shape and design that allows for maximum speed and lift,
while minimizing the effects of drag. Drag occurs when
objects are not streamlined.
The curved shape of the wing
of a bird or an airplane is called an airfoil.
As an airfoil moves through the air, the air over the rounded
surface must travel faster than the air along the flat
surface. This quicker movement of air over the top of an airfoil
creates a low-pressure area above the airfoil and a
high-pressure area below the airfoil. This
difference in pressure causes the wing to lift. Gliders and
helicopters and all winged aircraft use airfoils to create
Thrust is necessary to lift
heavier-than-air machines into the air. Engines
generate a force strong enough to create sufficient lift to
overcome the weight of the aircraft.