An airplane wing is shaped and angled that the air flowing over and under it is downward. According to Newton’s third , when the wing pushes air down, the air the wing up. This upward is called lift. At the time, the air moving over the top of the wing travels and has lower than the air below, which to the lift. The engines provide the that keeps air flowing past the wings.

Most passenger jets cruise at altitudes of about 10 to 12 kilometers. There are good reasons for flying so high.

The first is efficiency. At high altitude, the air is much thinner, so there is less drag, the force that resists a plane’s movement. Jet engines also work efficiently in the cold air found there. As a result, planes use less fuel per kilometer than they would at lower altitudes.

The second reason is comfort and safety. Most clouds and storms form in the lower part of the atmosphere, so flying above them usually means a smoother ride. Flying high also gives pilots more time and more options if something goes wrong.

However, the human body cannot function well in such thin air. At cruising altitude, the air pressure is so low that passengers would lose consciousness within a minute or so. For this reason, the cabin is pressurized to a level similar to that found about 1,800 to 2,400 meters above sea level. This is why some passengers notice their ears ‘popping’ as the plane climbs and descends.