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J. Perelman
"Entertaining physics". Book 2.
Chapter 7. Thermal phenomena


You heard, perhaps, that the best and sometimes the only means of combating forest or Prairie fire - GRT burning forest or steppe from the opposite side. New flame goes towards the raging sea of fire and destroying combustible material, deprives the fire of food; having met, both fire walls instantly extinguished, as if licking up each other.

Description of how to use this method of fighting fire with fire American steppes, many, of course, read in Cooper's novel "the Prairie". Is it possible to forget the dramatic moment when the old trapper was rescued from a fiery death travellers caught in the steppe fire? This is the place of the "Prairie".

"The old man suddenly took a bold look.

"Now is the time to act, " he said.

- You are too too late, miserable old man! - shouted at Middleton. The fire in the distance of a quarter of a mile from us, and the wind carries it to us with frightening speed!

- Here's how! Fire! Not very much I am afraid of him. Well, well done, fully! Attach me hands to this dried grass and bare earth.

In a very short time it was cleared place twenty feet in diameter. Trapper brought women on one edge of this small space, saying that they were covered with blankets in their dresses, can easily ignite. Having taken these precautions, he came to the opposite edge, where the element surrounded travelers high, dangerous ring, and, taking a pinch of the dry grass, put it on the shelf guns and set fire to. Flammable substance erupted immediately. Then the old man threw the blazing grass in the high hedge and, going to the center of the circle, was patiently await the result of his craft.

The destructive element eagerly pounced on the new food, and in an instant the flames began to lick the grass.

"Well, " the old man said, " now you will see how the fire will blow the fire.

But is it not dangerous? - exclaimed the astonished Middleton. - Not or bring you to us the enemy, instead of postponing it?

Fire, all increasing, began to spread in three sides, fading to fourth due to lack of food. As the fire grew and raged stronger and stronger, he was cleared before him all the space, leaving a black steaming the soil is much more naked than if the grass was mowed scythe.

The position of the fugitives would have become even riskier, if cleaned up their positions did not increase but as the flames surrounded him with other parties.

After a few minutes the flames began to recede in all directions, leaving people is shrouded in a cloud of smoke, but in complete safety from the stream of fire, continued furiously rushing forward.

The audience looked at a simple tool used by the trapper, with the same astonishment, with which, as they say, courtiers Ferdinand looked at the way Columbus put an egg".

The steppe fire extinguishing fire.

This method of extinguishing steppe and forest fires, however, not so simple as it seems at first sight. To use counter fire to extinguish the fire must only very experienced, or disaster may even intensify.

You will understand what it takes skill, if you ask yourself a question: why is the fire kindled by the trapper, ran toward the fire, and not in the opposite direction? Because the wind was blowing from the fire and drove the fire on travelers! It would seem that the fire caused by the trapper, was directed not towards the fiery sea, and back across the steppe. If that happened, they would be surrounded by a fiery ring and inevitably would have been killed.

What was the secret of the trapper?

In the simple knowledge of a physical law. Although the wind was blowing in the direction from the burning steppes to the travelers, but in the front, near the fire, there would be a reverse flow of air toward the flame. Indeed: heated above the sea of fire, the air becomes lighter and is displaced upward flowing from all sides fresh air from the steppe, not touched by the flames. Near the border of the fire is set so pull air toward the flame. To light a counter-fire, at a time when the fire close enough to have felt the pull of air. This is why the trapper was in no hurry to get to work ahead of time, and quietly waited for the right moment. Cost to set fire to the grass a little earlier, when the counter-thrust is not yet established, and the fire would extend in the opposite direction, making people desperate. But the delay could not be less than fatal: the fire came too close.

Entertaining physics J. Perelman


System Orphus


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