how do aeroplanes work

When you see a plane flying through the air, it looks like it's floating on nothing at all, but actually it's moving through a fluid. That's right, what looks like empty space is full of atoms and molecules--mostly nitrogen, oxygen, and carbon dioxide (and, these days, more and more carbon monoxide). In fact, a cubic foot (about .03 cubic meters) of air at sea level weighs a little more than an ounce (or about 35 grams). Air, like any other fluid, obeys certain laws. For example, if you blow smoke around the outside of a glass tube, the smoke (also a kind of fluid) will follow the contours of the tube. That is, the smoke will wrap around the two sides of the tube and meet at the other side. Let's call this "flow," since it has to do with the way fluids flow around solid objects. Fluids also like to spread out as far as possible. That is, fluids under higher pressure (where the molecules are closer together) tend to push out with greater force than fluids under lower pressure (where the molecules are spread out). Let's call this "spread." Wind is an example of spread. You've probably seen a weather map with high- and low-pressure systems: When they meet, the air under high pressure pushes out into the area of low pressure. We call that movement wind. Believe it or not, wings actually harness the principles of "flow" and "spread" to create enough force to pull hundreds of tons of metal off the ground. According to the flow principle, air flowing past the wing follows the contours of the wing itself. However, the air flowing over the curved top of the wing has a farther distance to travel than air moving along the flat bottom of the wing. As a result, the air at the top of the wing actually moves faster than the air at the bottom... The faster a fluid flows, the lower its pressure. That means the air at the bottom of the wing has a higher pressure than the air at the top of the wing. the high pressure air below the wing is actually pushing against the wing with more force than the low pressure air above the wing is pushing. The difference between these two forces is what we call "lift"--the force that lifts the plane off the ground and keeps it there. In order for a plane to fly, the lift must be greater than the weight of the plane. To achieve enough lift, the air must be flowing at a very high velocity past the wing.