Daniel Bernoulli was a Swiss physicist and mathematician who formulated and stated the following principle.
“The total energy in steady flowing fluid system is a constant along the flow path. An increase in the fluid’s speed must therefore be matched by a decrease in its pressure.”
What this means is: That when air flowing over a surface is sped up, the air uses more kinetic energy and the pressure above the surface decreases because there is less energy. The air below the surface has a higher air pressure and therefore the high air pressure pushes up on the surface towards the region of low air pressure to try and normalize.
We use this principle in the wings we use for airplanes.
If you have noticed, the wing of an airplane is curved.
So when air strikes the wing, the air above the surface has further to
travel than the air below the surface, therefore the air above the wing travels
faster and decreases the air pressure. The
air below the wing doesn’t have as far to travel and therefore there is a high
air pressure. The high air pressure
pushes up on the wing tying to take the place of the low air pressure and gives
the plane its lift. The higher air
pressure has more energy than the low air pressure and thus the air pushes up on
the wing. From this, we can also
see that the faster a plane flies, the more lift the wings produce.
That is why airport have long runways.
So that the airplane can gather enough speed for the wings to produce
enough lift to get the plane airborne.
This principle also applies to propellers which enable a plane to achieve forward thrust. The propellers are curved like an air foil which produces a pressure difference and thrust for the plane.
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Also the phenomena of ball spin used in sport can be explained by using Bernoulli’s principle. In a sport such as baseball, cricket, soccer or table tennis, the athlete deliberately spins the ball to make it curve in a particular direction. The air comes into contact with the spinning ball. The air moving in direction of the spin is sped up and the air in the opposite direction of the spin is slowed down. Because of this the air pressure on one side is higher than that on the other side. The high air pressure tries to compensate for the low air pressure and pushes the ball resulting in the curve.