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Bernoulli's principle relates the pressure of  fluid to its elevation and its speed. It states that  for an inviscid flow,  increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. Bernoulli's principle can be applied to various types of fluid flow, resulting in what is loosely denoted as Bernoulli's equation.It can be illustrated by an venturi meter example .ie ,a flow of air into a venturi meter. The kinetic energy increases at the expense of the fluid pressure, as shown by the difference in height of the two columns of water.  

                           Bernoulli's principle can also be derived from the principle of conservation of energy. This states that in a steady flow the sum of all forms of mechanical energy in a fluid along a streamline is  same at all points on that streamline. This inturn means that the sum of kinetic energy and potential energy remain constant. If the fluid is flowing out of a reservoir the sum of all forms of energy is the same on all streamlines because in a reservoir the energy per unit mass is the same everywhe

Applications of Bernoulli's Principle 

1. Airflight

 The  Bernoulli's principle works in air flight has to do with the architecture of the wings of the plane. On an airplane wing, the top of the wing is somewhat curved, while the bottom of the wing is totally flat. While in the sky, air travels across both the top and the bottom concurrently. Because both the top part and the bottom part of the plane are designed differently, this allows for the air on the bottom to move slower, which creates more pressure on the bottom, and allows for the air on the top to move faster, which creates less pressure. This is what creates lift, which allows planes to fly.

2 . Sailing

Bernoulli's principle is  the governing theory  behind sailing. , it works for creating lift in sails. All sail boats have two parts to it: a sail which points north and a keel which points on the opposite direction. If the speed of the air increases on the sail, there is less pressure on the sail, and conversely there is less pressure on the keel but a higher speed. Just like with an airplane this produces lift and propels the sail to move in the water.