by Harry Stevens

Created on: January 17, 2009

When was the last time that you travelled on an airplane? Last year? Last month? Last week? Whenever it was, you owe your plane ride to the principle developed by famous mathematician Daniel Bernoulli. The principle is appropriately called Bernoulli's Principle, and it relates the speed of a fluid (a liquid or a gas) to its pressure. It is the reason why such heavy planes are able to achieve lift in the seemingly weightless air.

Bernoulli's Principle is a simple one to understand. It states that the faster a fluid is moving, the lower its pressure is, and the slower a fluid is moving, the higher the pressure. This means that water that is moving in a river at 20 miles per hour will have a lower pressure than water that is travelling through a river at 10 miles per hour.

So how does this relate to the lift of airplanes? Well, the wing of an airplane is not entirely flat. The bottom surface of the wing is, but the top is slightly curved downwards. As the plane moves forward, air is passing by the wings on both sides. The air passes by the bottom side normally because the bottom is flat. However, the top is curved downwards, so as the air passes over it, it goes faster. This is because the air falls downwards because of gravity. Since the air above the wing of the plane is moving faster than the air below the wing, the pressure above the wing is lower than the pressure below the wing. Since fluids also want to move from areas of high pressure to areas of low pressure, the air below the plane pushes on the wing, and the plane rises through the air. The lift created by the differing air pressures is what creates the flight of the plane, even though the plane seems like it is too heavy to fly.

How else can Bernoulli's Principle be seen in the world? Well, have you ever gotten into the shower, and as you turned the water on, the shower curtain came towards you? That occurs because of Bernoulli's Principle. The fluids that are inside the shower are moving at a faster speed than the ones outside the shower curtain. Therefore, the pressure inside the shower is less than the pressure outside. Because fluids want to move from areas of high pressure to areas of low pressure, the air tries to rush into the shower, and the curtain is pushed.

Bernoulli's Principle is the most important principle in aviation. It gives planes the ability to fly, when it seems like it is impossible for them to leave the ground.

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