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


Here come the memory of the heroic leaps of our masters parachuting, vybrasyvalsya at an altitude of about 10 km, without opening the parachute. Only flying a considerable part of the way, they pulled the ring of the parachute and the last hundreds of meters down, hovering on their umbrellas.

Many people think that falling of the stone, without opening the parachute man flies down in the empty space. If it were so, if the human body was falling in the air, as in a vacuum - long jump would have lasted much less than in reality, and develop by the end of the speed would be great.

However, air resistance prevents the growth of speed. The speed of the body of the parachutist during skydive grows only during the first ten seconds, during the first hundred meters. Air resistance increases with speed so much that pretty soon there comes a point when the speed no longer changes. The movement of the accelerated becomes uniform.

By calculation to outline in General terms the picture skydive from the point of view of mechanics. Accelerated fall parachutist lasts for only the first 12 seconds or slightly less, depending on its weight. During this ten seconds, he manages to fall metres 400 - 500 and buy a speed of about 50 meters per second. The rest of the way to the chute opening is held for uniform motion at that speed.

About the same fall and rain drops. The only difference is that the first period of the fall, when the speed is still growing, continues to rain drops just about one second or even less. The final speed of the drops of rain so not so great as in the long jump parachute: it ranges from 2 to 7 meters per second depending on the size of the drops.

Entertaining physics J. Perelman


System Orphus


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