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In the following few paragraphs some of the many ways will be described so that you, the reader, will realize physics at work in the world of flight. First of all you will have to understand the principles of flight. An airplane flies because air moving over and under its surfaces, particularly its wings, travels at different velocities, producing a difference in air pressure, low above the wing and high below it. The low pressure exerts a pulling influence, and the high pressure a pushing influence. The lifting force, usually called lift, depends on the shape, area, and tilt of the wing, and on the speed of the aircraft. The shape of the wing causes the air streaming above and below the wing to travel at different velocities. The greater distance over which the air must travel above the curved upper surface forces that air to move faster to keep pace with the air moving along the flat lower surface. According to Bernoulli’s principle, it is this difference in air velocity that produces the difference in air pressure. Bernoulli’s principle is the concept that as the speed of a moving fluid (liquid or gas) increases, the pressure within that fluid decreases. This principle was originally formulated in 1738 by the Swiss mathematician and physicist Daniel Bernoulli, it states that the total energy in a steadily 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. This principle also covers the flow over surfaces, such as airplane wings. Airplane wings are designed to direct air to flow more rapidly over its upper surface than over its lower surface. As a result, the air above the wing travels at an increased speed, producing a region of reduced pressure. The pressure below the wing, which is therefore greater, exerts an upward force, or lift, on the wing. Lift is the third factor in which physics aids the flight of an aircraft. Lift is influenced by a variety of different things, such as area, tilt of the wing, and on the speed of the aircraft. Wing area influences lift; the more of the wing that is exposed to the air, the greater the lift. The up or down tilt of the wing, usually called its angle of attack, contributes to or detracts from lift. As a wing is tilted upward, that is, as its angle of attack is increased, its lift increases. The air passing over the top of an uptilted wing must travel a greater distance and thus produces a greater pressure differential between the upper and lower surfaces. Airplane speed has a great influence on lift. The faster the air moves over and under the surfaces of an airplane, the greater the pressure differential and, as a result, the greater the lift. As an airplane flies on a level course, the lift contributed by the wing and other parts of the structure counterbalance the weight of the plane. Within certain limits, if the angle of attack is increased while the speed remains constant, the plane will rise. If the angle of attack is decreased, that is, the wing is tilted downward, the plane will lose lift and start to descend. An airplane will also climb from level flight if its speed is increased, and it will dive if its speed is decreased. Lift varies directly with speed. Drag is another factor which is contributed by the flight of an airplane. Drag is the force that tends to retard the motion of the airplane through the air. Most drag is a result of the resistance of the air to objects moving through it. This type of drag can be reduced by streamlining the aircraft. It is also reduced by placing slots in the wing so that the boundary layer or “wall of air” building up in front and around the wing can flow through it. One form of drag, however, known as induced drag, is a direct result of the lift produced by the wing. In effect, induced drag is the penalty exacted for lift. Great differences in the pressure of the air flowing over and under a wing can cause whirlpools or eddies of air to billow up along the trailing edges of the wings. These whirlpools produce a braking or force toward the rear that must be overcome by the forward thrust of the engines. As the angle of attack of an airplane is increased, the plane gains lift, but the lift is limited. As the angle is increased, air turbulence spreads over the wing. Then at a certain critical point (an angle of about 14 degrees in many airplanes), the wing loses lift and the plane stalls, nosing over into a dive. As a conclusion, I hope these previous paragraphs have given you the knowledge that everyone dealing with physics or airplanes should possess. These factors may not show all that physics has to contribute in the flight of an aircraft but they do show the major contributions. After reading these paragraphs, you should now have greater respect for physics, not just in airplanes, but in the world, because it is all around you and nothing can exist or work without it. Bibliography: Word Count: 952
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