Bernoulli's Principle, discovered by Swiss physicist Daniel Bernoulli (1700-1782), states that the pressure exerted by a liquid flowing along the walls of a tube (e.g., a pipe or hose ) decreases as the velocity of the liquid increases (as at the exit of an opening). This Principle explains the "lift" obtained by hydrofoils and winged aircraft.
The principles of fluid hydromechanics are applied in hydraulics , which deals with water and other liquids at rest or in motion.
HYDRODYNAMICS
A liquid or gas flows from areas of high pressure to areas of low pressure. This happens, for example, when water is squeezed out of a sponge or when a “jet” of water comes out of a hose.
Fluid flow is influenced by viscosity, the resistance to fluid motion. Some fluids flow by capillary action, which is largely dependent on adhesion and surface tension.
The flow of a fluid or gas can also be laminar (smooth) or turbulent. The nature of the flow depends on: the viscosity and density of the fluid , the speed of the fluid's motion, and the surface and shape of the objects in contact with the fluid. For example, water flows turbulently down a river, but flows in a laminar fashion around a boat with curved, smooth sides. An object whose shape offers little resistance to the flow of a liquid is said to be efficient.
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Bernoulli's Principle
The effect explained by Bernoulli can be produced by sending a fluid through a Venturi tube (a short tube, the diameter of which is significantly narrowed at a certain section in the middle, so that the sections before and after the narrowing have a larger diameter) (see image). The velocity of the fluid in the narrow section of the tube is higher and its pressure is lower than in the rest of the tube. The Venturi tube is used in various devices, including instruments that measure fluid flow.
The effect explained by Bernoulli can be produced by sending a fluid through a Venturi tube (a short tube, the diameter of which is significantly narrowed at a certain section in the middle, so that the sections before and after the narrowing have a larger diameter) (see image). The velocity of the fluid in the narrow section of the tube is higher and its pressure is lower than in the rest of the tube. The Venturi tube is used in various devices, including instruments that measure fluid flow.
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Torricelli's Theorem
Torricelli's Theorem, devised by the Italian physicist Evangelista Torricelli (1608-1647), is applicable to incompressible and non-viscous flows and calculates the flow rate of a liquid exiting an orifice. "The velocity of a liquid in an open vessel, through an orifice, is that which any body would have, falling freely in a vacuum from the level of the liquid to the centre of gravity of the orifice." In other words, the theorem states that a liquid flowing from an outlet into a tank has the same velocity as an object falling freely from the level of the liquid surface to the level of the outlet.
Continued in The principles of hydromechanics (II) .
Source: howstuffworks.com
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