Bernoulli Principle

The Bernoulli principle states that a rise in pressure in a flowing fluid must always be accompanied by a decrease in the speed, and conversely, an increase in the speed of the fluid results in a decrease in the pressure (Bernoulli's Principle). This equation is derived from the principle of conservation of energy in that the total mechanical energy of an object remains constant as the object moves, provided that the net work done by external, non-conservative forces (e.g. friction) is zero. The usual form of the Bernoulli equation is

= velocity at point p

= pressure

= density

= acceleration of gravity

= height above an arbitrary reference level

Because there are many basic assumptions involved in the derivation of Bernoulli’s equation, it is important to remember the following:

- It assumes viscous (friction) effects are negligible;

- It assumes the flow is steady;

- The equation applies along a streamline;

- It assumes the fluid to be incompressible; and

- It assumes no energy is added to or removed from the fluid along the streamline. (Finnemore and Joseph)

The Bernoulli principle, also known as the Bernoulli equation is an important principle of fluid dynamics which is applied to everyday things. Examples of Bernoulli’s principle can be found in the airplane, which stays aloft due to pressure differences on the surface of the wing. It is found in household plumbing and even explains the reason the shower curtain billows inward while taking a shower (Bernoulli Principle: Definition and Much More from Answers.com).

The influence pressure and fluid flow has had on us is enormous. One example shows how household plumbing makes use of Bernoulli’s equation. The U-shaped region under our sinks is known as the “trap” because water collects there, and serves as a blockage against sewer gas escaping into the house. When water from a machine flows through the sewer pipe, the fast velocity causes the pressure at that point to drop. The pressure at the trap is higher due to a higher elevation. Because of this unbalance in pressure, the water is forced out of trap and into sewer line, leading to an opening in sewer gas. A properly designed plumbing system has a vent to the outside of the house. The vent makes sure the pressure in the sewer pipe and trap is constant, even when water from a machine is flowing through the sewer pipe. Thus, the vent disallows the trap from emptying, which will not allow a 2nd path for sewer gas (Physics Tutorial: Bernoulli's Equation).

Airplanes are able to generate lift force based on Bernoulli’s principle. The air flowing past the top of the wing of an airplane is moving much faster than the air flowing past the under-side of the wing. The air pressure above the wing is much lower than the pressure underneath, therefore, creates lift force (Bernoulli's Principle - Wikipedia).

The Bernoulli principle is applied every time one takes a shower if your shower has a curtain. When the water is turned, the fast moving air created by the water creates a center of lower pressure and causes the curtain to move away from the slower moving air outside. Because of difference in pressure, the shower curtain moves away from the slower moving air outside. This is an example of the way that Bernoulli’s principle