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Bernoulli Principle
The creation of an additional lift force on a projectile in flight resulting from Bernoulli's concusion that the higher the velocity of air flow, the lower the surrounding pressure

Lift Force: an additional force created by a pressure gradient forming on opposing surfaces of an aerofoil moving through a fluid

Bernoulli built his work off of that of Newton. In 1738, he published “Hydrodynamica”, his study in fluid dynamics, or the study of how fluids behave when they are in motion. Air, like water, is a fluid; however, unlike water, which is a liquid, air is a gaseous substance. Air is considered a fluid because it flows and can take on different shapes. Bernoulli asserted in “Hydrodynamica” that as a fluid moves faster, it produces less pressure, and conversely, slower moving fluids produce greater pressure.

Bernoulli’s theorem, in fluid dynamics, relation among the pressure, velocity, and elevation in a moving fluid (liquid or gas), the compressibility and viscosity (internal friction) of which are negligible and the flow of which is steady, or laminar. First derived (1738) by the Swiss mathematician Daniel Bernoulli, the theorem states, in effect, that the total mechanical energy of the flowing fluid, comprising the energy associated with fluid pressure, the gravitational potential energy of elevation, and the kinetic energy of fluid motion, remains constant. Bernoulli’s theorem is the principle of energy conservation for ideal fluids in steady, or streamline, flow and is the basis for many engineering applications.

Bernoulli’s theorem implies, therefore, that if the fluid flows horizontally so that no change in gravitational potential energy occurs, then a decrease in fluid pressure is associated with an increase in fluid velocity. If the fluid is flowing through a horizontal pipe of varying cross-sectional area, for example, the fluid speeds up in constricted areas so that the pressure the fluid exerts is least where the cross section is smallest. This phenomenon is sometimes called the Venturi effect, after the Italian scientist G.B. Venturi (1746–1822), who first noted the effects of constricted channels on fluid flow.

Australian Institute of Sport head biomechanist Dr Bruce Mason said Jones' knock-knees should allow her greater power in the water, under Bernoulli's principle of propulsion in physics. "Having the knock-knees ... gives you an advantage in being able to rotate the feet around," Dr Mason said. "The feet themselves act very much like propeller blades on a boat. If you can increase the range at which you move the feet ... that creates more propulsion. "Using Bernoulli's principle, the person can produce greater force than other people because they've got greater range of movement."

Scientists use such terms as "symmetric airfoil", the "Bernoulli principle", "wind velocity" and "frictional force" to explain the phenomenon. Martin, a 25-year-old native of Albury-Wodonga on the Murray River, explained it in language much easier to process.

"If you throw the discus into a headwind it can add five metres to the distance it travels," he said.

"Events can be won on a sudden gust of wind but you need to be able to read it and you have to respond to it. It takes an entire career to master the art of catching the wind . . . but when you do, it's spot on.

A lift force does not always have to work in an upwards direction. The Bernoulli principle can also be used to describe a downward lift force, such as that required by speed skiers, cyclists and racing cars. The car, bike and skis need to be pushed down into the ground so a greater frictional force is created. In a Formula 1 sports car, for example, the spoiler is angled so the lift force can act in a downward direction to push the car into the track.

In response to an article published at Cricinfo, Rabindra Mehta, a NASA scientist and former club fast bowler based gives the definitive answer to the mysteries of swing.