The Reason Planes Fly
Whenever I see a plane the first question that comes to mind is "What is causing that thing to stay off of the ground?"
Well I finally discovered the answer. When a plane flys there are four forces at work that keep the plane flying. These forces are lift, thrust, gravity, and drag.

Lift & Pressure
Airplane wings are created with a special design called an airfoil. The airfoil design bulges out more on the top than on the bottom. This causes the air that hit the wing to go off into two different streams, one that goes over the top and one that goes under and they both meet up in the back.

The air moving over the top of the wing is caused to go faster than the slower moving air on the bottom. Faster moving air has less pressure, so this causes the pressure on the bottom of the wing to be greater and the plane is lifted. This effect is known as the Bernoulli Principle. This principle was developed by Daniel Bernoulli who was a Swiss mathematician and physician. He developed the principle in the 18th century. When a plane creates lift it overcomes the force of gravity that is pulling the plane down.

Air pressure plays a big part in flight also. When you think about flight you have to realize that air pressure is a force that is pushing on every square inch of an airplane. When a plane is parked the air pressure is distributed evenly around the plane surface. When the plane is in flight the pressure on top of the wings pushes down less and the pressure on the bottom of the wings pushes more. This is what causes the plane to feel a lift.

Drag
Another force that has a great part in flight is drag. Drag is the force that is pulling the plane backwards. Drag is created when the air collides with the airplanes wings and creates friction. This friction causes the plane to slow down and feel a drag. When wings are produced the designers have to make the wings create lift but also minimize friction with the air.

Thrust
Thrust is the force that causes a plane to move forward and is created by the planes propeller or jet engines. Thrust is created by a propeller by using the same concept as lift. The propellor is specially shaped like an airfoil but it uses the lift to pull the plane forward instead of pushing the plane up.