Describe in your own words opu's fascination for the formula to fly?
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Answer:
Flight is a phenomenon that has long been a part of the natural world. Birds fly not only by flapping their wings, but by gliding with their wings outstretched for long distances. Smoke, which is composed of tiny particles, can rise thousands of feet into the air. Both these types of flight are possible because of the principles of physical science. Likewise, man-made aircraft rely on these principles to overcome the force of gravity and achieve flight.
Lighter-than-air craft, such as the hot air balloon, work on a buoyancy principle. They float on air much like rafts float on water. The density of a raft is less than that of water, so it floats. Although the density of water is constant, the density of air decreases with altitude. The density of hot air inside a balloon is less than that of the air at sea level, so the balloon rises. It will continue to rise until the air outside of the balloon is of the same density as the air inside. Smoke particles rise on a plume of hot air being generated by a fire. When the air cools, the particles fall back to Earth.
Heavier-than-air flight is made possible by a careful balance of four physical forces: lift, drag, weight, and thrust. For flight, an aircraft's lift must balance its weight, and its thrust must exceed its drag. A plane uses its wings for lift and its engines for thrust. Drag is reduced by a plane's smooth shape and its weight is controlled by the materials it is constructed of.
Lift
In order for an aircraft to rise into the air, a force must be created that equals or exceeds the force of gravity. This force is called lift. In heavier-than-air craft, lift is created by the flow of air over an airfoil. The shape of an airfoil causes air to flow faster on top than on bottom. The fast flowing air decreases the surrounding air pressure. Because the air pressure is greater below the airfoil than above, a resulting lift force is created. To further understand how an airfoil creates lift, it is necessary to use two important equations of physical science.
The pressure variations of flowing air is best represented by Bernoulli's equation. It was derived by Daniel Bernoulli, a Swiss mathematician, to explain the variation in pressure exerted by flowing streams of water. The Bernoulli equation is written as:
where: P = pressure (force exerted divided by area exerted on)
rho = density of the fluid
V = velocity of the moving object or fluid
To understand the Bernoulli equation, one must first understand another important principle of physical science, the continuity equation. It simply states that in any given flow, the density (rho) times the cross-sectional area (A) of the flow, times the velocity (V) is constant. The continuity equation is written as:
where: P = pressure
V = velocity
A = cross sectional area of flow
Using the Bernoulli equation and the continuity equation, it can be shown how air flowing over an airfoil creates lift. Imagine air flowing over a stationary airfoil, such as an aircraft wing. Far ahead of the airfoil, the air travels at a uniform velocity. To flow past the airfoil, however, it must "split" in two, part of the flow traveling on top and part traveling on the bottom.
The shape of a typical airfoil is asymmetrical - its surface area is greater on the top than on the bottom. As the air flows over the airfoil, it is displaced more by the top surface than the bottom. According to the continuity law, this displacement, or loss of flow area, must lead to an increase in velocity. Consider an airfoil in a pipe with flowing water. Water will flow faster in a narrow section of the pipe.