Physics

Bernoullis Principle of Lift



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Albert Einstein, Leonardo da Vinci, Daniel Bernoulli, Isaac Newton.... Hey, wait a minute! Who the devil is Bernoulli? Unless you're a science geek, trivia freak or into airplanes, it is unlikely that you've ever heard of Daniel Bernoulli. Daniel Bernoulli was a Swiss mathematician and physicist. Born into a family of scientists and mathematicians in the year 1700, he discovered the principle by which hard-balls curve and why shower curtains "drift" into the tub when the hot water is turned on. His theory also explains how a carburetor works and why tornadoes suck the roofs from houses. Oh yes, it also explains why airplanes can fly...

The basics of the Bernoulli Principle is that when the velocity (or speed) of a liquid or gas increases, the pressure decreases. To simplify this, in terms of airplanes, when air passes over an airfoil, the decrease in pressure on the top of the airfoil combines with the increase in pressure under the airfoil to produce "lift".

An airfoil is a device that when moved through the air is capable of achieving "lift" or in some cases of increasing traction by creating "down-force". Airfoils can include not just the wings of the plane, but also the horizontal AND vertical tail surfaces and propellers. Other examples of airfoils are sails or the blades of fans, compressors and turbines. Airfoils are designed to increase the speed of the airflow across the top of it's surface, thus decreasing the pressure above it. An airfoil is shaped like a teardrop laid on edge - a rounded thicker leading-edge, tapering to a narrower, slightly pointed trailing-edge. The "lift" and "drag" of an airfoil is effected by the shape and camber.



I'm not real big on the math theory behind Bernoulli's Principle of Lift, so a friend took me out to show me how it works. If you have ever held your hand out of the car window while you're driving down the highway you have experienced first-hand Bernoulli's Principle of Lift. If you incline your hand to the wind, your hand (acting as an airfoil) deflects the wind, which pulls your hand up and back. The upward motion is the "lift" and the backward motion is called "drag". So the next time you're driving down the road with your hand out the window, or sitting on the runway waiting to take-off, just remember that Daniel Bernoulli is the guy who figured out why planes fly and tornadoes suck.

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