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If you have ever tried and succeeded, or tried and failed, to make the perfect paper airplane, then you know something about how plane design takes into account the forces of nature. But flying a paper airplane is one thing; flying an 870,000-pound airplane in the sky is another.
The force that keeps an airplane flying in the air is called lift. On airplanes, the wings create most of the lift required to keep the plane aloft. To understand lift, we can look back two centuries before the Wright brothers ever took to the air.
Wings on commercial jet planes have a special shape called an airfoil. An airfoil is curved on the top and flat on the bottom. When it meets an oncoming mass of air, it slices through it, causing some of the air to go over the top and the rest of the air to go along the bottom. But, according to the laws of physics, the air moving over the curved top part of the wing actually moves faster than the air on the bottom flat part of the wing.
Daniel Bernoulli, an 18th century scientist, noticed this phenomenon and found that when the speed of a fluid, which can be water or air, is faster, the pressure of the fluid is lower. So the faster-moving air above the wing exerts less pressure on the wing than the slower-moving air below. The result is an upward push on the wing—and voila, you have lift!
There are many ways to increase the lift of a wing, such as changing the angle at which the wing cuts through the air or increasing the plane's speed. In addition, pilots can manipulate the shape of the plane's wings.
The wings on jet planes have flaps called ailerons. During takeoff and landing, the ailerons are extended rearward and downward from the back edge of the wings, changing the wing's curvature. This enables the plane to maintain lift at lower speeds and allows an airplane to make a slower landing approach and a shorter landing.
We can thank Daniel Bernoulli for providing one explanation of how an airplane stays in the air; but did you know that his principles also explain how a toilet flushes and how a racecar stays on the track? You never know where Bernoulli might show up next.
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