Objects that fly using wings get their lift by taking advantage of Bernoulli's principle. Bernoulli's principle says that as a fluid's velocity increases its pressure decreases.
Airplanes and birds have an airfoil shape to
each of their wings to produce lift. The airfoil shape produces
unequal lengths across the top and bottom of the wing. Air
splitting
at the front of the wing must rejoin
at the back of the wing so as not to create a vacuum. Since the top
surface is curved upward and is longer it forces the air to move
faster across the top than the bottom. Faster moving fluids create
less pressure, so the bottom of the wing creates greater pressure
producing lift.
Racing cars use this principle to produce
better traction. They place an airfoil on the back of the car but
with the curved surface on the bottom. This is commonly called a
spoiler. With the curved surface underneath, greater pressure is
generated on the top forcing the back of the car down onto the road.
There are four major forces involved in
flight.
1. Lift
2. Weight (gravity)
3. Thrust
4. Drag
Lift
In order to fly an object must be able to generate enough lift to
overcome its weight. To accomplish this, air must be moving across
the wing. This can be done by pushing the wing through the air such
as with a jet engine or by moving the air acroos the wing such as
with wind. The opposing force of ligt is gravity.
Weight
Weight is the force of gravity. It is a continous downward force that
flying objects must constantly overcome to stay aloft. Objects can
glide for a very long period of time but will eventually fall back to
earth if they are don't generate enough lift to overcome gravity. The
opposing forve of gravity is lift.
Thrust
Thrust is the force that moves the object forward. This is generated
by a jet engine, propellar or the backward push of a bird wing. To
move forward the flying object must overcome drag. To help reduce
drag, airplanes are streamlined and most bird shapes have evolved to
be streamlined. The opposing force to thrust is drag.
Drag
Drag is actually friction between the moving object and the air. It
is also referred to as air resistence. The more streamlined, or aerodynamic, an object is the less air
resistennce the object generates. The opposite force of drag is
thrust.
