Physics

Bernoullis Principle of Lift



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Hundreds of people flying thousands of feet above the ground is no longer surprising for today's generation. But think of the time when Leonardo Da Vinci could predict the graphical image of modern airplane. It might not be more than a fantastic dream for the 15th century people to imagine themselves flying in the sky. Though, thanks to our scientists for their extraordinary brains and strong determinations that today we enjoy the reality born from the dreams our ancestors seen for them.

Daniel Bernoulli, a Swiss scientist and mathematician in 1738 discovered the theory of difference in pressure that is caused by still and moving air. According to him moving air experiences less air pressure than the still air. This very concept is the most important reason behind the successful flight of the flyer designed by the Wright brothers in 1903 to the most sophisticated Air force one of the 21st century. Still there are other important factors and principles involved in lifting the heavy air vessel off the ground to reach for the sky.

Taking consideration of Bernoulli's principle of lift, the wings of airplane are specially designed, popularly known as airfoil structure. The airfoil structure of the wing, which means the wing bulges out more on the top part than on the bottom part, so that air has to travel a greater distance on the top part of the wing from the leading edge to the trailing edge. As the lower portion of the wing has a less curve, air takes a little time to reach the trailing edge and therefore the air velocity in the lower portion of the wing is less than air velocity in the top part of the wing. This difference in air velocity creates more pressure in the lower part that pushes or lifts the upper portion of the wing. This lift is caused to take the aircraft high against the force of gravity. Similarly there is another portion of the air craft, where Bernoulli's principle comes into play. It is the propeller of an airplane. Propeller is important in moving a plane forward and the force, which accomplishes this task is known as thrust. The propeller of the aircraft may have two or more blades similar to the airfoil structure of the wing. But in this case lift is created to propel the plane in forward direction. Newton's third law of motion is again an important reason behind pushing the plane ahead. The force at which the exhaust gases comes out from behind the plane creates an equal and opposite force to assist the plane's advancement.

Lift generating from the wings depends on many factors like the type of wing, area of wing, speed of the air craft, air density, air friction etc. when air is more dense, more is the lift and air density increases as the plane goes higher. The faster a plane moves more air pass over the wings with a higher velocity resulting a greater lift. As the plane propels faster, it experiences more air friction, known as drag. Drag and lift works hand in hand to move a plane. Drag or the frictional force is balanced out by thrust and the plane moves ahead. Lift can not be created on a still object, because air pressure is distributed uniformly, when a plane is at rest. According to aerodynamic principle, it is the motion of an object that creates difference in air pressure and creates a lift. Hence, lift is also dependent on the thrust to act.

However a lot many concepts and works are associated, when a plane opens its wings to fly. Still it is the centuries old scientific experiment and achievement, which will forever remind us the journey from complexity of dreams to the simplicity of reality.

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