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J. Perelman
"Entertaining physics". Book 1.
Chapter 3. The resistance of the medium


Did you try to explain to myself why the kite flies up when he pull the string forward ?

If you can answer this question, you will understand why flying an airplane, why rush through the air the seeds of maple and even partially make sure you understand the reasons for the weird movements of the boomerang. All of these are phenomena of the same order. The very air that is so serious obstacle to the flight of projectiles, causes flight not only easy fruit maple or paper kite, but heavy plane with dozens of passengers.

To explain the uplift of a paper kite, have to resort to a simplified drawing. Let the line MN in the figure we cut snake.

What forces act on a kite?

When running the serpent, we pull it by the cord, it moves due to the heaviness of the tail in an inclined position. Let this movement is performed from right to left. Denote the angle of inclination of the plane of the snake to the horizon through and. Consider what forces act on snakes in this movement. The air must, of course, to hinder his movement, to provide for snakes some pressure. This pressure is depicted in the figure as arrows OS; as the air pressure is always perpendicular to the plane, then the line OS drawn at right angles to the MN. The power Windows can be decomposed into two by constructing the so-called parallelogram of forces; get instead of the power of OS two forces, OD and OP. Power OD pushes our snakes back and, therefore, reduces the initial speed. Another force, the EOS apparatus carries up; it reduces its weight and, if large enough, can overcome the weight of the serpent and raise it. That is why the serpent rises up when we pull him by the rope forward.

The plane is the same serpent, only the driving force of our hands replaced it the driving force of the propeller or jet engine, which tells the machine to move forward and, therefore, like a serpent that causes it to rise up. This gives only a rough scheme of the phenomenon; there are other circumstances contributing to the rise of the aircraft; it will be discussed in another place.

Entertaining physics J. Perelman


System Orphus


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