Physics

Bernoullis Principle of Lift



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Daniel Bernoulli was born in Groningen, the Netherlands, in 1700 and died in Basel, Switzerland in 1782. He is remembered for his mathematical work in fluid mechanics, as well as his contributions in the fields of probability and statistics.

Besides his other notable achievements, he is best known for his "Bernoulli Principle." He was working in fluid dynamics at the time, though his equations can also be applied to other forms of flow. In simple language, the Bernoulli Principle stated that when the speed of a fluid increased, the gravitational pressure on the fluid decreased. It deals with the conservation of energy principle and was established 100 years before man was able to fly.

When applying the Bernoulli Principle to the flight of an airplane, the ability of the plane to utilize a lift force, is due to the fact that the air is flowing faster on the top of the wings, where pressure is very low, and flowing slower on the underside, where the pressure is higher. These differences in air pressure create the "lift" needed for the plane to move through the air and fly. The faster the air speed passes over the top of the wings, the lower the pressure beneath them, causing a natural "lift."

Air density, temperature and wing shape also contribute to the amount of lift a plane receives. Cold air is very dense and allows the plane to climb better. The wings on a plane are shaped, as they are, to ensure that the air passing over the top of wing reaches the sloped edge at the same time as the air going under the flat belly of the wing. The air going over the top has to go a further distance than the air on the underside and must be forced to flow faster than the slower moving air beneath in order for them both to reach the wing's edge at the same time. The difference in air speeds, balances out the different pressures, by creating an upward force on the wings.

The Bernoulli Principle has more recently been used to explain how Mother Nature's violent storms are able to rip roofs off of houses and buildings. Hurricanes and tornadoes are composed of high-speed winds that create pressure differences on the top and underneath of a roof. The faster airflow attacks the outside, top of the roof but the air underneath is slower moving and a lift force occurs.

Bernoulli's Principle can also be seen while driving your car. Have you ever noticed a convertible, with the top closed, traveling at a high rate of speed, sort of bulging on top? The wind is passing over the cloth top at a higher speed and lower pressure than the inert air inside the car, causing the bulge. The same principle explains that "pull" you may have felt when in your car, either stopped or slowing down to make an exit and a fast moving vehicle passes you. The vehicle in motion, at a higher speed, creates a lower pressure as it passes you, and you feel the "tug."

Daniel Bernoulli authored numerous books and papers and won many prizes and honors throughout his lifetime. The Bernoulli Principle gave humans a better understanding of flow and pressure, allowing us to conquer the skies.

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