The human body can tolerate for a relatively long time. Physics tasks with astronomy elements. Assisting with altitude sickness

The human body is very delicate. Without additional protection, it can function only in a narrow temperature range and at a certain pressure. It must constantly receive water and nutrients. And it will not survive a fall from a height of more than a few meters. How much can the human body withstand? When does our body face death? Fullpiccha brings to your attention a unique overview of the facts about the limits of survival of the human body.

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1. Body temperature.

Survival limits: body temperature can vary from + 20 ° C to + 41 ° C.

Conclusions: usually our temperature ranges from 35.8 to 37.3 ° C. Such a temperature regime of the body ensures the smooth functioning of all organs. At temperatures above 41 ° C, significant fluid loss, dehydration and organ damage occur. At temperatures below 20 ° C, blood flow stops.

The human body temperature is different from the ambient temperature. A person can live in an environment with temperatures ranging from -40 to + 60 ° C. It is interesting that a decrease in temperature is just as dangerous as its rise. At a temperature of 35 ° C, our motor functions begin to deteriorate, at 33 ° C we start to lose orientation, and at a temperature of 30 ° C, we lose consciousness. A body temperature of 20 ° C is the limit below which the heart stops beating and a person dies. However, medicine knows a case when a man was saved, whose body temperature was only 13 ° C. (Photo: David Martín / flickr.com).

Survival limits: 40 to 226 beats per minute.

Conclusions: a low heart rate leads to a decrease in blood pressure and loss of consciousness, too high - to a heart attack and death.

The heart must constantly pump blood and circulate it throughout the body. If the heart stops working, brain death occurs. The pulse is a wave of pressure induced by the release of blood from the left ventricle into the aorta, from where it is distributed throughout the body by arteries.

Interestingly, the "life" of the heart in most mammals averages 1,000,000,000 beats, while a healthy human heart performs three times as many beats in its entire life. A healthy adult heart beats 100,000 times a day. In professional athletes, the resting heart rate is often as low as 40 beats per minute. The length of all blood vessels in the human body, if they are connected, is 100,000 km, which is two and a half times longer than the length of the Earth's equator.

Did you know that the total power of the human heart over 80 years of human life is so great that it could drag a steam locomotive to the highest mountain in Europe - Mont Blanc (4810 m above sea level)? (Photo: Jo Christian Oterhals / flickr.com).

Survival limits: each person is different.

Conclusion: Information overload leads to the human brain falling into a state of depression and no longer functioning properly. The person is confused, begins to carry delirium, sometimes loses consciousness, and after the disappearance of the symptoms, he does not remember anything. Prolonged brain overload can lead to mental illness.

On average, the human brain can store as much information as 20,000 average dictionaries contain. However, even such an efficient body can “overheat” due to the excess of information.

Interesting: shock resulting from extreme irritation nervous system, can lead to a state of numbness (stupor), while the person ceases to control himself: he can suddenly leave, become aggressive, speak nonsense and behave unpredictably.

Did you know that the total length of nerve fibers in the brain ranges from 150,000 to 180,000 km? (Photo: Zombola Photography / flickr.com).

Survival limits: 190 decibels.

Conclusions: at a noise level of 160 decibels, eardrums begin to burst in humans. More intense sounds can damage other organs, particularly the lungs. The pressure wave tears the lungs apart, causing air to enter the bloodstream. This, in turn, leads to blockage of the blood vessels (embolism), which causes shock, myocardial infarction, and ultimately death.

Typically, the range of noise we experience ranges from 20 decibels (whisper) to 120 decibels (airplane taking off). Anything that is above this border becomes painful for us. Interesting: being in a noisy environment is harmful to a person, reduces his effectiveness and distracts. A person is not able to get used to loud sounds.

Did you know that loud or unpleasant sounds are still used, unfortunately, during the interrogation of prisoners of war, as well as during the training of special services soldiers? (Photo: Leanne Boulton / flickr.com).

Survival limits: loss of 3 liters of blood, that is, 40-50 percent of the total amount in the body.

Conclusions: a lack of blood leads to a slowdown in the heart, because it has nothing to pump. The pressure drops so much that the blood can no longer fill the chambers of the heart, which leads to its arrest. At the same time, the brain does not receive oxygen, stops working and dies.

The main task of the blood is to distribute oxygen throughout the body, that is, to saturate all organs with oxygen, including the brain. In addition, blood removes carbon dioxide from tissues and carries nutrients throughout the body.

Interesting: the human body contains 4-6 liters of blood (which is 8% of the body weight). The loss of 0.5 liters of blood in adults is not dangerous, but when the body lacks 2 liters of blood, there is a great risk to life, in such cases medical attention is needed.

Did you know that other mammals and birds have the same blood-to-body weight ratio - 8%? And the record amount of blood lost in a person who did survive was 4.5 liters? (Photo: Tomitheos / flickr.com).

Survival limits: -18 to 4500 m above sea level.

Conclusions: if a person without training, who does not know the rules, and also without special equipment dives to a depth of more than 18 meters, he is in danger of ruptured eardrums, damage to the lungs and nose, too high pressure in other organs, loss of consciousness and death from drowning. Whereas at an altitude of more than 4500 meters above sea level, a lack of oxygen in the inhaled air for 6-12 hours can lead to pulmonary and cerebral edema. If a person cannot descend to a lower altitude, he will die.

Interesting: an unprepared human body without special equipment can live in a relatively small range of heights. Only trained people (divers and climbers) can dive to a depth of more than 18 meters and climb the tops of the mountains, and even they use special equipment for this - diving cylinders and climbing equipment.

Did you know that the record in one-breath diving belongs to the Italian Umberto Pelizzari - he dived to a depth of 150 m.During the dive, he experienced tremendous pressure: 13 kilograms per square centimeter of body, that is, about 250 tons for the whole body. (Photo: B℮n / flickr.com).

Survival margin: 7-10 days.

Conclusions: lack of water for a long time (7-10 days) leads to the fact that the blood becomes so thick that it cannot move through the vessels, and the heart is unable to distribute it throughout the body.

Two-thirds of the human body (weight) consists of water, which is necessary for the proper functioning of the body. The kidneys need water to remove toxins from the body; the lungs need water to moisturize the air we exhale. Water also participates in the processes taking place in the cells of our body.

Interesting: when the body lacks about 5 liters of water, a person begins to feel dizzy or faint. With a lack of water in the amount of 10 liters, severe convulsions begin, with a 15-liter water shortage, a person dies.

Did you know that in the process of breathing we consume about 400 ml of water every day? Not only the lack of water can kill us, but its excess. Such an incident happened to one woman from California (USA), who during the competition drank 7.5 liters of water in a short period of time, as a result of which she lost consciousness and died a few hours later. (Photo: Shutterstock)

Survival limits: 60 days.

Conclusions: The lack of nutrients affects the functioning of the whole organism. In a starving person, the heart rate slows down, blood cholesterol levels rise, heart failure and irreversible damage to the liver and kidneys occur. A person exhausted by hunger also has hallucinations, he becomes lethargic and very weak.

A person eats food to provide himself with energy for the work of the whole body. A healthy, well-nourished person who has access to sufficient water and is in a friendly environment can survive without food for about 60 days.

Interesting: the feeling of hunger usually appears a few hours after the last meal. During the first three days without food, the human body expends energy from the food that was last eaten. Then the liver begins to break down and consume fat from the body. After three weeks, the body begins to burn energy from the muscles and internal organs.

Did you know that American Amerykanin Charles R. McNabb, who in 2004 went on hunger strike for 123 days in prison for the longest time without food, survived? He only drank water, and sometimes a cup of coffee.

Did you know that about 25,000 people die of hunger every day in the world? (Photo: Rubén Chase / flickr.com).

In addition to the magnitude of acceleration and the duration of the overload action, they are also characterized by such factors as the rate of increase of the overload in time and the direction of the overload action. Fitting well to the body can reduce the effects of congestion. By the duration of the action, overloads can be divided into three conditional groups:

Instantaneous - calculated in hundredths of a second or in milliseconds.
They are often found in everyday life and reach rather high values. Instantaneous overloads completely lose the property of a field of forces, their duration of action is practically absent, there is only a peak of growth, which is a push, a blow. The damaging effect of such overloads is perceived by the surface of the body and spreads deep into it in the form of a wave, similar to the impact of a moving body on a motionless one.

Short-term - effective tenths of a second, which, when using protective equipment, can reach relatively large values.
Short-term overloads approach the action of external forces and are characterized mainly by a local effect. On ejection seats, a healthy person can withstand an overload of 20-25 g without consequences. Athletes endure an overload of 90-100 g during extreme diving. The record for a short-term overload of 179.8 g belongs to a race car driver who crashed into the track fence at a speed of 173 km / h, having received 29 fractures and three dislocations. Pretty soon he recovered from his injuries and a year later took part in new competitions.

Long-term - seconds or minutes affecting the body within the limits of small and medium values.
It can be considered established that an overload of up to 4.5 g can be carried over a fairly long period without harm to the body, and that the speed of visual and auditory reactions at an overload of 1.6 g remains the same as at rest. For about 5 minutes, astronauts are subjected to overloads of 5-6 g, in emergency situations 12 g. Due to the increase in blood weight, blood circulation slows down. Normal blood pressure in humans at the heart level is 0.12 atm. Since the head is about 30 cm higher than the heart, then at an acceleration of 4 g, this pressure is only enough for blood to reach the brain. To ensure the blood supply to the brain at an acceleration of 8 g, the heart must more than double its blood pressure. With a vertical acceleration of 5 g, the blood “becomes heavier” so that the heart cannot drive it to the head at all, and the person experiences a sensation of a “black veil” before his eyes and loses consciousness. If the action of acceleration is directed upward, a "red veil" rises before the eyes and loss of consciousness occurs as a result of a rush of blood to the head. Already under the influence of acceleration exceeding 1 g, the astronaut may develop visual impairments. At an acceleration of 3 g for more than 3 seconds, severe peripheral visual impairment may occur. In general, with an increase in overload, visual acuity decreases. When accelerating, the astronaut develops visual illusions. To weaken the effect of high accelerations, the astronaut is placed in the spacecraft in such a way that the G-forces are directed upward. The astronaut, lying on his back, is in an almost horizontal position. The angle between his back and thigh is approximately 100 °, and between the thigh and lower leg is 117 °. The back slope is approximately 12 °. This position provides an effective blood supply to the astronaut's brain at accelerations up to 10 g, and even for a short time up to 25 g.
Animals turn out to be much more resilient in relation to overload. Thus, experiments on dogs subjected to the action of centrifugal acceleration showed that these animals are able to easily withstand 80-fold overload for 2 minutes. and 40 times within 5 minutes. With an overload of 98 g for 5 min. there was a rapid death from anemia of the brain, lungs and heart muscles, but organ rupture was not observed.

1. On what trajectory do the planets move around the Sun?

2. It is known that the first, second and third cosmic velocities are respectively equal to 7.9; 11.2 and 16.5 km / s. Express these speeds in m / s and km / h.

3. What is the speed of the ISS (International Space Station) and the Soyuz-TM-31 transport spacecraft after docking relative to each other?

4. The cosmonauts of the Salyut-6 orbital space station observed the approach of the Progress transport vehicle. “The speed of the ship is 4 m / s,” said Yuriy Romanenko. With respect to what body did the cosmonaut mean the speed of the spacecraft - relative to the Earth or relative to the Salyut station?

5. Imagine that four identical satellites of the Earth are launched from the cosmodrome located at the equator to the same height: to the north, south, west, and east. In this case, each subsequent satellite was launched in 1 min. after the previous one. Will satellites collide in flight? Which one was easier to launch? Consider orbits circular. (Answer:satellites launched along the equator will collide, but those that launch to the north and south cannot collide, since they will rotate in different planes, the angle between which is equal to the angle of rotation of the Earth in 1 min. In the direction of the Earth's rotation, that is, to the east, it is easier to launch the satellite, since the speed of the Earth's rotation is used, which complements the speed imparted by the launch vehicle. The hardest thing to launch a satellite to the west ).

6. The distance between the stars is usually expressed in light years. A light year is the distance traveled by light in a vacuum in one year. Express the light year in kilometers. (Answer:9.5 * 10 12 km).

7. The Andromeda nebula is visible to the naked eye, but is at a distance of 900 thousand sv from the Earth. years. Express this distance in kilometers. (Answer:8.5 * 10 18 km ) .

8. The speed of the artificial Earth satellite is 8 km / s, and the rifle bullet is 800 m / s. Which of these bodies is moving faster and how many times?

9. How long does it take for light to travel the distance from the Sun to the Earth? (Answer:8 min 20 s ).

10. The closest star to us is in the constellation Centaurus. The light from it goes to the Earth for 4.3 years. Determine the distance to the given star. (Answer:AU 270,000 ).

11. The Soviet spacecraft Vostok-5 with Valery Bykovsky on board orbited the Earth 81 times. Calculate the distance (in AU) traversed by the spacecraft, assuming a circular orbit that is 200 km away from the Earth's surface. (Answer:0.022 a.u .) .

12. Expedition Magellan made trip around the world in 3 years, and Gagarin circled the globe in 89 minutes. The paths traversed by them are approximately equal. How many times the average flight speed of Gagarin exceeded the average swimming speed of Magellan? (Answer: 20 000) .

13. The star Vega, in the direction of which our solar system is moving at a speed of 20 km / s, is located at a distance of 2.5 * 10 14 km from us. How long would it take us to be close to this star if it did not itself move in world space? (Answer:in 400,000 years).

14. What is the distance the Earth travels when moving around the Sun in a second? per day? in a year? (Answer:30 km; 2.6 million km; 940 million km).

15. Find the average speed of the Moon around the Earth, assuming the Moon's orbit is circular. The average distance from the Earth to the Moon is 384,000 km, and the 16th orbital period is equal to a day. (Answer:1 km / s ) .

16. How long does it take for a rocket to acquire its first cosmic speed of 7.9 km / s if it moves with an acceleration of 40 m / s 2? (Answer:3.3 minutes ) .

17. How long would it take for a spacecraft, propelled by a photonic rocket with a constant acceleration of 9.8 m / s 2, to reach a speed equal to 9/10 the speed of light? (Answer:320 days ) .

18. A space rocket accelerates from rest and, having covered a distance of 200 km, reaches a speed of 11 km / s. With what acceleration did it move? What is the acceleration time? (Answer:300 m / s 2; 37s ) .

19. The Soviet spacecraft-satellite "Vostok-3" with cosmonaut Andriyan Nikolaev on board made 64 revolutions around the Earth in 95 hours. Determine the average flight speed (in km / s). Consider the spacecraft's orbit circular and 230 km from the Earth's surface. (Answer:7.3 km / s).

20. At what distance from the Earth should the spacecraft be in order for the radio signal sent from the Earth and reflected by the spacecraft to return to Earth in 1.8 s after its departure. (Answer:270,000 km).

21. Asteroid Icarus revolves around the Sun in 1.02 years, being on average at a distance of 1.08 AU. From him. Determine the average speed of the asteroid. (Answer:31.63km / s ) .

22. Asteroid Hidalgo revolves around the Sun in 14.04 years, being on average at a distance of 5.82 AU. From him. Determine the average speed of the asteroid. (Answer:12.38 km / s ) .

23. Comet Schwassmann-Wachmann moves in an orbit close to circular with a period of 15.3 years at a distance of 6.09 AU. from the sun. Calculate the speed of its movement. (Answer:11.89 km / s ).

24. How long does it take for a rocket to acquire its first cosmic speed of 7.9 km / s if it moves with an acceleration of 40 m / s 2? (Answer : 3.3s).

25. A satellite moving near the earth's surface in an elliptical orbit is decelerated by the atmosphere. How will this change the flight path? ( Answer: Decreasing the speed converts the elliptical trajectory to a circular one. A further continuous decrease in speed translates the circular orbit into a spiral. This explains the fact that the first satellites existed for a limited time. Getting into the dense layers of the atmosphere, they heated up to an enormous temperature and evaporated).

26. Is it possible to create a satellite that will move around the earth for as long as you like? ( Answer:It is practically possible. At an altitude of the order of several thousand kilometers, air resistance has almost no effect on the satellite's flight. In addition, small rockets can be installed on the satellite, which will, as required, equalize the satellite's speed to the required).

27. The human body can tolerate a fourfold increase in its weight for a relatively long time. What maximum acceleration can be given to the spacecraft in order not to exceed this load on the astronauts' bodies, if they are not equipped with means of weakening the load? To analyze cases of vertical take-off from the Earth's surface, vertical descent, horizontal movement and flight outside the gravitational field. (Answer:According to Newton's second law, we find that with a vertical start from the Earth, acceleration 3g 0 is permissible, with a vertical descent 5g 0, when moving around the Earth at its surface - g 0, outside the gravitational field –4g 0 ).

Annotation to the work.

The idea of ​​creating a collection of problems on an environmental topic came to me a long time ago. These tasks have also been accumulating for a long time. Each teacher is faced with the problem of finding material, including tasks on a specific topic, corresponding to a future lesson or extracurricular activity. Few people did not delve into the mountain of literature in order to find the necessary fact or problem suitable to the topic.

Environmental issues in physics lessons, voluntarily or involuntarily, have to be touched upon, because progress is impossible without the development of technology, just as the development of technology is impossible without physics. Majority environmental issues we have just because of the consequences of technological progress.

In the course of my pedagogical activity, I determined the range of topics in the school physics course, where it is imperative to touch on environmental problems and, as a result, I began a gradual selection of problems that accumulated as I worked. This is how my Ecological Problem Book came about. The problem book is divided into sections that coincide with the main sections of physics. I think that finer splitting is impractical, since for some topics there are only one or two tasks (for example, Measurements). And it is often difficult to clearly see the line between themes, since natural phenomena always occur in connection with each other.

Problems from the collection, I think, will be useful for teachers working at school. Tasks can be used not only in the classroom, but also in extracurricular activities.

Explanatory note.

Ecology (from ancient Greek. Οἶκος - dwelling, dwelling, house, property and λόγος - concept, doctrine, science) - the science of the relationship of living organisms and their communities with each other and with the environment.

Since ancient times, people have begun to notice various patterns in the interaction of animals with each other and with the environment. However, in those days even biology was not a separate science, being a part of philosophy.

In modern times, which is characterized by an upsurge in the field of scientific knowledge, environmental patterns were identified by scientists-encyclopedists, for example: R. Boyle - he conducted one of the first environmental experiments - the effect of atmospheric pressure on animals, resistance to vacuum of aquatic, amphibians and other poikilothermic animals ...

Ecology is usually viewed as a sub-branch of biology, the general science of living organisms. Living organisms can be studied at various levels, ranging from individual atoms and molecules to populations, biocenoses and the biosphere as a whole. Ecology also studies the environment in which they live and its problems. Ecology is associated with many other sciences precisely because it studies the organization of living organisms on a very high level, explores the connections between organisms and their habitat. Ecology is closely related to such sciences as biology, chemistry, mathematics, geography, physics, epidemiology, biogeochemistry. Consider the relationship between ecology and physics.

After all, physics, the introduction of its results into industry are presented as one of the main sources of environmental pollution. Indeed, the nuclear industry, energy, and other industries that make extensive use of the achievements of physics provide many examples of negative impact on the environment.

Physics is a science of nature, therefore, in connection with the increasing potential of technical progress and the development of technology carrying an ecological catastrophe, it is necessary to consider the problem of environmental protection in the lessons of this particular subject.

To prevent possible negative consequences of human invasion of nature, it is necessary to solve a number of scientific, technical, socio-political and other problems, among which one of the first places is occupied by pedagogical, educational. The younger generation, while still at school, should be prepared for a scientifically grounded and respectful attitude towards the natural environment. That is why the idea of ​​forming an ecological culture among schoolchildren has acquired extremely important significance at the present time.

Environmental education and upbringing of schoolchildren in the process of teaching physics is associated, first of all, with the formation in them of ideas about the integrity of nature, the relationship between the phenomena occurring in it and their causation, about the interaction of man and nature and, as a result, a violation of some balance of natural processes. The ecological orientation of teaching physics is strengthened mainly as a result of consideration of natural phenomena, as well as the influence of human activity on the world around us. This allows schoolchildren to understand more deeply, more fully and correctly the increasingly complex interactions between society and nature, know about the danger of ill-conceived human intervention in her life, and know how to navigate the information about the protection and use of natural resources, which they receive from popular science literature. , radio and television broadcasts, can assess the environmental impact of certain technical solutions and use their physical knowledge to actively protect the environment.

In this regard, the object of my work is environmental education in the process of teaching physics. The subject is the means and methods of environmental education.

Purpose of the work: search for ways to solve the problem of environmental education in the educational process, development of a system of means and methods of environmental education. Since there is a problem of ecological education, I set a goal to develop a collection of physics problems with ecological content for the teacher. The material being developed is systematized and divided into separate paragraphs.

The systematic application of the proposed problems in physics lessons raises the general level of ecological culture, arouses interest in the subject of physics and the quality of its teaching.

Environmental objectives and issues can be applied to the following topics:

Mechanics.

A drop of oil with a volume of 0.003 mm 3 spreads over the surface of the water, forming a thin film with an area of ​​300 cm 2. Assuming the thickness of the layer is equal to the diameter of 1 molecule - 0.0000001 mm, Estimate what area the spreading oil with a volume of 1 m 3 will occupy.

The leaves, lifted by the wind, in 5 minutes, moving evenly, moved to a distance of 7500 m. What is the speed of the hurricane?

The speed of the Earth in its orbit around the Sun is 300 times faster than the speed of a racing car speeding at a speed of 360 km / h. Calculate, based on this, the length of the earth's orbit and the distance from the earth to the sun.

Dolphins have been found to be very fast. 100 meters, for example, they swim in 10 seconds. Considering that the density of water is 800 times higher than the density of air, how to explain the reason for the high swimming speed of dolphins?

Small sea fish walk in a flock, the external shape of which resembles a drop. Why is this flock formed?

What is the importance of the bristles on the surface of the body of an earthworm for its movement?

As you know, some birds, during long-distance flights, are placed in a chain or school. What is the reason for this location?

What is the purpose of duck or goose swimming membranes?

Why does a strong wind break trees more often in summer than in winter?

Why does oat suffer little from the wind: it almost never breaks or lodges?

With what effort does the corn sprout come out of the soil?

The jumping limbs of a grasshopper are very long. Why?

Why is it impossible to hold the same weight in an outstretched hand as in a bent one?

As you know, molars overcome significantly more resistance than incisors. It is possible, for example, in some cases to gnaw a nut that has not succumbed to the action of the incisors. Explain why?

Why are turtles tipped over on their backs usually unable to roll over on their own?

When a tree has a higher center of gravity: in summer or autumn, when the leaves have fallen?

In a dense forest, you can always find trees felled by the wind, and in an open field, where the wind is much stronger, trees rarely fall down. How can this be explained?

Which tree - spruce or pine - is more stable?

How much pressure can a wasp create when it stings?

Many bones of animals and humans have thickenings at the ends. Explain the purpose of these thickenings?

Beavers are known to often gnaw through thick trees. Why don't the beaver's teeth become blunt?

Although a whale lives in water, it breathes with its lungs. Despite the presence of lungs, the whale will not live even an hour if it accidentally ends up on land. Why?

If a deep-sea fish is quickly pulled to the surface of the sea, then its internal organs will swell and the fish will die. How can this be explained?

As you know, air under high pressure is constantly pumped into a suit of a diver working at great depths. This air resists the pressure of the water on the suit and prevents the water from flattening it. But the air in a diver's suit presses in all directions with equal force. Consequently, the diver must experience its great pressure, and yet this does not happen. What's the matter here?

Why does a diver experience a painful sensation only when he plunges into or rises from the water, but not when he is at depth?

An elephant can remain underwater and breathe through a trunk protruding above it. Why, when people tried to imitate an elephant, replacing the trunk with a long rubber tube tightly fitting to the mouth, then there was bleeding from the mouth, nose, ears, which ended in a serious illness?

How does an elephant use atmospheric pressure whenever it starts drinking water?

Why can fish breathe oxygen dissolved in water?

Which air is richer in oxygen: the one we breathe, or the one that fish breathe?

Why do fish in an aquarium sometimes swim near the surface of the water?

Most algae have thin, flexible stems. Why doesn't algae need hard stems?

Calculate the force of pressure from the atmosphere experienced by a person whose body surface is equal to 2 m 2.

Everyone saw in the summer small flies hanging in the air as if motionless. With a jerk, the insects jump to the side and freeze in place again. How can insects remain motionless at one point?

What is the importance of atmospheric pressure for the articulation of bones in our body?

Why on high mountains the action of the joints is disturbed: the limbs do not obey well, dislocations are easily obtained?

Why does the artilleryman open his mouth when firing a gun?

In the open seas and oceans, there is a very interesting stuck fish. This strange fish attaches itself to various objects, especially sharks and ships, and holds on with such force that it is difficult to pull it off. Due to what forces does it stick to a moving object?

Everyone knows that a common fly walks freely on the ceiling. Will she be able to move freely along the ceiling in an airless space?

Due to what force is the mature acorn held in the "cup" after the connective tissue dies off?

A cow is a cloven-hoofed animal, a horse is a one-hoofed animal. When moving through swampy and swampy places, the cow easily raises its legs, and the horse - with great difficulty. Why?

Why in a river with a muddy bottom do we get stuck in a shallow place more than in a deep one?

Why can a person, whose body is lighter than water, drown if he cannot swim, and the horse and other animals immediately begin to swim, even if they have never been in the water before?

What role does the swim bladder play in fish?

Why does a diving dog easily pull a drowning person out of the water, but, having dragged him to the shore, cannot even move him from his place?

If you watch waterfowl, you will notice that they are not very submerged in water. Explain why?

The seeds of many plants have light wings. What is their purpose?

Some large seabirds often "accompany" ships, chasing them for hours, or even days. At the same time, attention is drawn to the fact that these birds overcome the path together with the steamer with low energy consumption, flying with mostly fixed wings. Due to what energy do the birds move in this case?

The spider's legs do not have muscle fibers. However, the spider not only moves quickly, but even jumps. How can this be explained?

Why does a lonely deciduous plant form a large snowdrift in winter, although the snow cover is much thinner throughout the surrounding area? How does this benefit the plants?

Why can't a bird caught in a well fly out of it?

Why does a cat always land on its feet when it falls?

Why does a person, getting into a space where the pressure is much lower than atmospheric pressure, for example, high mountains, often has pain in the ears and even in the whole body?

How does the human breathing apparatus work?

Oil of 1 m 3 was spilled onto the surface of the water. What area will the oil occupy if the layer thickness is considered equal to 1 \ 40,000 mm?

Scientists have calculated that there are 10,000,000 hairs on the root of a wheat stalk that serve the plant for nutrition. What is the total length of these hairs, and what is the cross-sectional area of ​​a hair if its average length is 2 mm, and their total volume is 1.5 cm 3?

Most cereal plants have a tall, tubular stem with a heavy head at the top. What is the purpose of the tubular stem?

How to determine the density of an unknown liquid using only a glass, water and a balance with weights?

When studying the cloud, it was found that the average volume of a water droplet in it is 0.000004 mm 3. What mass of water is contained in a cloud with a volume of 1 m 3, if a cloud of 0.1 cm 3 contains on average 140 droplets?

Coming out of the water, the dog shakes itself. What phenomenon helps her in this case to free the wool from water? Explain the answer.

A fox, running away from a dog pursuing her, often saves herself by making sharp sudden movements to the side just at those moments when the dog is ready to grab it with its teeth. Why is it difficult for a dog to catch a fox?

Why shouldn't weeds be pulled out of the ground too harshly when weeding, even when they are weakly retained in the soil?

In what way do some leguminous plants use the property of inertia to spread their seeds?

How important is the bouncy hair on the soles of the hare's feet?

Why does the wing of a butterfly move slower in flight than the wing of a wasp?

How can one explain the greater mobility of small animals, in comparison with larger ones?

“Who does not know,” wrote Galileo Galilei, “that a horse, falling from a height of three to four cubits, breaks its legs, while the dog will not suffer, and the cat remains unharmed, being thrown from eight to ten cubits, just like a cricket that fell from the top of the tower, or an ant that fell to the ground at least from the lunar sphere. Why do smaller insects, falling to the ground from a great height, remain unharmed, while large animals die?

Watch the swimming of fish, leeches. How is Newton's third law used in their motion?

Why does a squirrel need a large tail? And the fox?

Why does pike swim in the river faster than other fish?

Why do some fish press their fins when they move quickly?

Why is it difficult to hold live fish in your hands?

The fish can move forward, throwing jets of water with its gills. Explain this phenomenon.

What is the purpose of webbed feet in waterfowl?

A bird sitting on a branch fluttered and flew away. Where and at what point did the branch deviate? Why?

What is the cause of earthquake destruction?

A person takes an average of 15 breaths per minute. With each inhalation, 1600 cm 3 of air enters his lungs. What mass of air passes through a person's lungs in one hour?

Why do large raindrops fall faster than small ones? (take into account the force of air resistance).

From a high cliff, it is safer to jump into loose sandy embankments than onto solid ground. Why?

Why are ships (tankers) intended for the transportation of oil separated by partitions into separate compartments - tanks?

A motor ship in a collision with a boat can sink it without any damage to itself. How does this fit in with equality of action and reaction?

In a day, a young bamboo can grow 86.4 cm. How much will it grow in a second?

Determine the speed of the river in the Volga in the section where the speed of the cargo ship downstream is 600 km / day, and 336 km / day upstream.

Let's assume that the thickness of the ice in the pond increases by an average of 5 mm per day. What is the thickness of the ice in a week if its initial thickness is 2 cm?

The fox chases the hare at such a speed that its impulse is equal to that of the hare. Will the fox be able to catch up with the hare?

Do a bucket of drinking water and a bucket filled with sea water have the same mass?

Why does a bird of prey, falling like a stone from the sky, spread its wings near the ground?

What is the fundamental difference between the way a person and an octopus move in water?

Calculate the water pressure: a) at the deepest depth of the Pacific Ocean - 11035m; b) at the greatest depth of the Sea of ​​Azov - 14m (the density of water in it should be taken equal to 1020 kg / m 3)

Why is the explosion of a projectile under water destructive for organisms living in water?

A storm wind with a force of 10 points creates a pressure on the obstacle of about 1000 Pa. Determine the force of pressure on the wall of a house 5 meters high and 10 meters long, if the wind blows perpendicular to the surface of the house?

Vessels with an attached bottom are submerged in water to the same depth. The bottom of the vessels disappears if you pour 1 kg of water into each of them. Will the bottom fall off if the water is replaced with mercury?

What role does atmospheric pressure play in drinking?

What force causes the ebb and flow in the seas and oceans of the Earth?

Is the fish in the water in a state of weightlessness?

Does gravity act on a swift flying in the air?

The human body can tolerate a fourfold increase in its weight for a relatively long time. What maximum acceleration can be given to a spacecraft at launch from the Earth's surface so as not to exceed this load on the astronauts' organism? Consider the launch of the spacecraft vertical.

Does the free surface of the ocean repeat the "sphericity" of the Earth?

Why is it impossible to extinguish burning kerosene by pouring water over it?

An ice floe floats in the water. The volume of its above-water part is 20 m 3. What is the volume of the underwater part?

How would the water level in the ocean change if all the icebergs melted?

What depth in the sea corresponds to a water pressure of 412 kPa?

A hawk, weighing 0.4 kg, is lifted by an air stream to a height of 70 m. Determine the work of the force that lifted the bird?

During floods, the spillway dam of the Volzhskaya hydroelectric power station passes through every second a volume of water equal to 45,000 m 3. Knowing that the height of the dam is 25 m, determine the power of the water flow.

The water discharge in the river is 500 m 3 / s. What power does the water flow have if the water level is raised by the dam by 10 m?

Scientists have calculated that a whale, swimming under water at a speed of 27 km / h, develops a power of 150 kW. Determine the strength of the water's resistance to the movement of the whale.

What is the significance of the breakwaters (breakwater structures) installed along the seashore? The energy of which body is the cause of the destruction of the coast? What is the source of energy for this body?

Determine the kinetic energy of a meteorite weighing 50 kg, moving at a speed of 40 km / s.

What is the potential energy of a 20 mg raindrop at an altitude of 2 km?

What is the efficiency of a hydroelectric station if the water flow is 6 m 3 / s, the water pressure is 20 m, and the power of the station is 880 kW?

Determine the net power of a water engine with an efficiency of 20% if water falls on its blades from a height of 5 meters. The initial water velocity at this height is 1 m / s. The water leaving the engine has a speed of 2 m / s, and the flow rate per second is 2 m 3 / s.

Why don't we hear the rumbling of powerful processes occurring on the Sun?

Does a bird create longitudinal or transverse waves in flight by flapping its wings?

Even in complete darkness, fish detect the approach of danger with the help of their bodies. What waves do fish "see"?

How will representatives of the fauna of earthquake-prone regions find out about the impending earthquake?

Why, if a person did not see the explosion of a powerful projectile, does the blast wave take him by surprise?

Why did nature reward man with not one, but two hearing organs - the right and left ear?

It was found that a bee flying with a bribe (collected by it flower sap) (into the hive, flaps its wings on average 300 times per second, and unloaded - about 440 times per second. with prey or fly after it?

Why don't we perceive as sound those vibrations of the air that are created by the wings of a flying bird?

Why is it difficult to determine where the sound is coming from in the forest?

In a coniferous forest, even with a weak wind, a rumble is heard. The forest is noisy, we say then. Forest noise arises mainly not from the friction of individual needles against each other. And from what?

At what distance from the ship is the iceberg if the ultrasonic signal sent by the sonar was received back after 2.8 s? Accept the speed of sound in water equal to 1500 m / s.

In recent years, there have been many recorded bird collisions with turboprop and turbojet aircraft. Sometimes it happens that birds simply "attack" airports. How can this be explained?

The bee's wings vibrate at a frequency of 240 Hz. How many flaps of its wings will a bee make until it reaches a flower field located at a distance of 500 m, if it flies at a speed of 4 m / s.

Near the ore deposit, the period of oscillation of the pendulum changed by 0.1%. The density of the ore in the deposit is 8 g / cm 3. Estimate the radius of the deposit if the average density of the Earth is 5.6 g / cm 3.

Why don't bats run into obstacles even in complete darkness?

Accidentally flying through the window, a bat often sits on people's heads. Why?

As you know, bats have very poor eyesight, and they orient themselves only thanks to an ultrasonic locator. With its help, mice surprisingly accurately determine the location of even the smallest insects and catch them on the fly without missing. But sometimes there are failures. And, as a rule, with butterflies. Why doesn't the ultrasonic bat locator always detect them?

What is the purpose of the two large spherical bubbles located on the sides of the frog's head?

What is the significance of the mobility of the auricles for many animals ?:

It is known that at the moment of danger the roundhead lizard quickly burrows into the ground. How does she do it?

Does the human ear respond to wavelength or frequency?

Determine the maximum and minimum wavelengths perceived by humans. The speed of sound is 340 m / s, the cutoff frequencies are 20Hz and 20,000 Hz.

Near a straight section of the sea coast at a distance L from it

there was an explosion. Assuming that the bottom of the sea differs slightly from the inclined plane, find the length of the coastal section to which the waves generated by the explosion will reach. Consider that the depth of the sea at the site of the explosion is small enough.

Octopuses, squids, cuttlefish move by throwing out with force the water that they collect through the hole in the mantle. Where in technology is the same principle of movement used?

Molecular physics

Where are the more atoms: in a glass of water or in a glass of mercury?

A lake with an average depth of 5 meters and an area of ​​4 km 2 was "salted" by throwing a crystal table salt weighing 10 mg. After a long time, a glass of water with a volume of 200 cm 3 was scooped up from the lake. How many sodium ions were there in this glass?

At what volume of the gym is the number of molecules in the air inside the gym 100 times greater than the number of atoms in an iron bar weighing 100 kg? Assume that the air is under normal conditions.

At room temperature and normal atmospheric pressure, the outflow of methane in a household gas stove is not more than 1.1 ∙ 10 -8 m 3. Determine the number of gas molecules that appeared in the room as a result of such a leak, if the stove was turned on for three hours.

In a room with an area of ​​100 m 3 and a height of 4 m, 1 liter of acetone is poured. How many acetone molecules are contained in 1 m 3 of air if all acetone has evaporated and is evenly distributed throughout the room? The chemical formula of acetone (CH) 2 CO.

Explain why kerosene is used to detect through defects in the capillary method of welding quality control?

The sea animal squid, when attacked, emits a dark blue protective liquid. Why, after a while, the space filled with this liquid, even in calm water, becomes transparent?

The dog takes a fresh, although invisible, trail (for example, of a hare). However, over time, she cannot smell it. Explain this phenomenon.

Why is a can of kerosene often covered with a thin layer of kerosene on the outside?

Why do we feel the scent of flowers at a distance?

If, on a sunny summer day, you measure the temperature of bare soil and nearby soil covered with plants, it turns out that the bare soil is hotter. But if in these places the temperature of the soil is measured at night, then, on the contrary, the soil under the plants will have a higher temperature than bare. How can this be explained?

Why do ducks willingly climb into the water in severe frost?

Does a bear's body temperature drop during hibernation?

Lizards and some other small animals living in deserts climb to the tops of bushes during the hottest part of the day. Why?

In winter, the wind is much colder for us than in the calm. Will there be a difference in temperature readings?

How do whales, walruses, seals living in water with ever-floating ice constantly maintain a high body temperature (38-40 0 С)?

Why don't reindeer freeze even in severe frost? What protects them from the cold?

Why do small organisms need better protection from heat loss than large ones?

For what purpose are raspberry bushes bent to the ground for the winter in the northern regions?

How can you explain that some species of birds (black grouse, wood grouse, hazel grouses, partridges, etc.) burrow into snowdrifts and sometimes spend several days there?

Why do polar foxes have significantly smaller ears than foxes living in temperate climates?

Why does the water in the sea get warmer after a strong storm?

During the ice drift, it is colder near the river than away from it. Why?

Why is heat more difficult to endure in humid air than in dry air?

For what purpose do winter wheat seeds burrow a little deeper into the soil than spring wheat seeds?

Why is icy dangerous for plants?

In severe frost, birds often freeze on the fly than sitting still. How can this be explained?

Why do many animals sleep curled up in a ball in cold weather?

What is the purpose of the thick subcutaneous fat layer in whales, seals and other animals living in the waters of the polar seas?

Why is there a very large daily temperature range in deserts?

Why do locals in Asian countries wear hats and wadded robes during extreme heat?

What is harmful to plants, especially cereals: heavy snow or snowless winter?

Why do animals living in cold countries have thicker hair than animals living in hot countries?

If a clear night is expected in the spring or fall, the gardeners make fires, which produce a lot of smoke that envelops the plants. What for?

In severe frost, birds often freeze on the fly than sitting still. Why do you think?

For which plants are spring frosts most dangerous: for those planted on dark soils or on light ones?

Why is a horse sweating from work covered in a blanket or fur coat in the cold?

How can one explain the fact that when a drought sets in, the leaves of many plants curl?

The leaves of most desert plants are covered with thick silvery hairs (wormwood, sand acacia, etc.). How does this affect the rate of evaporation of water by plants?

Why do many desert plants have thorns or thorns instead of leaves?

Why, even on cloudy, but not rainy days, the grass cut in the meadow dries up faster than the grass cut in the forest?

After harrowing, the soil evaporates less moisture. Why?

Why does a dog stick out his tongue in extreme heat?

During the eruption of a volcano on the island of Krakatoa in Indonesia (1883), a huge amount of the smallest dust was thrown out. Why has this dust been in the atmosphere for several years?

If the ventilation does not work, the finest wood dust in the carpentry shop "hangs" in the air for hours even after the woodworking machines are turned off. Why?

Why is a cylinder of any compressed gas a great fire hazard?

What pressure should a 50 liter gas cylinder withstand so that 2 kg of methane (CH 4) can be stored in it at a temperature of 25 ° C?

The bottle, filled with gas, is tightly closed with a stopper with a cross-sectional area of ​​2.5 cm 2. To what temperature should the gas be heated in order for the cork to fly out of the bottle, if the friction force holding the cork is 12N? The initial air pressure in the bottle and the outside pressure are the same and equal to 100 kPa, and the initial temperature is 3 ° C.

What causes strong heating and burning artificial satellites Earth when they enter the lower atmosphere?

Cars, planes, motorcycles are painted with nitro varnish, which gives a smooth shiny surface. What goal, besides beauty, is pursued in this case?

The match lights up when rubbed against the boxes. It also flares up when you bring it into a candle flame. What are the similarities and differences in the reasons that led to the ignition of the match in both cases?

Such a phenomenon can be observed in late autumn. Snow. A day passed, another - warming came - the snow melted. But despite the fact that the frost was -1-2 0 С, many plants remained green. How did they manage to resist? After all, they are 80% water.

Human teeth consist of a solid substance - dentin, and their surface is covered with a layer of even harder, but fragile enamel. Why do teeth deteriorate if cold food is taken after hot food and vice versa?

Why does dew on the leaves of many plants collect in drops, and not spread over the entire leaf?

Some small insects, getting under water, cannot get out. How can this be explained?

On the lake or in the pond, you have probably seen insects more than once - water striders, which, fingering with their long legs, quickly run in the water. They do not swim, but run, touching the water only with the tips of their feet. Explain why their paws are not submerged in water, but rest on it like on a hard surface?

Why do swallows fly low before the rain?

Why do cities where the air is polluted with dust and smoke receive less solar energy?

Why on a summer day the water temperature in the reservoirs is lower than the temperature of the sand on the shore? What happens at night?

Why are air cleaning fans usually placed near the ceiling?

Why does ice appear first on the surface in ponds, holes, lakes?

Why for the winter the near-trunk circles of the earth near fruit trees are covered with layers of peat, manure or sawdust?

Why is snow retention carried out on fields in arid regions of the country not only good remedy accumulation of moisture in the soil, but also a means of combating the freezing of winter crops?

Why do sparrows sit "crumpled" in winter?

How are breezes formed?

Why does dirty snow melt faster in sunny weather than clean snow?

Which soils are better warmed up by the sun's rays: chernozem or podzolic, with a lighter color?

Why is water in open reservoirs heated by the sun's rays more slowly than land?

Quartz cookware is durable and will never burst. There is a lot of quartz on Earth. Why don't they make utensils from quartz?

What are double window frames for? Will the room get warmer in winter if the gap between the frames is significantly increased?

Warm air is known to rise upward. Why is the temperature -50 0 С at an altitude of 10 km?

Why does the proximity of water bodies affect the air temperature?

Why is the climate of the islands milder than the climate of the interior of the continents?

Grouse in winter, going to sleep, falls like a stone from a tree and gets stuck in the snow. What happened to the bird's potential energy?

It is known that the temperature of motorcycle exhaust gases leaving the muffler is several times lower than the temperature reached in the engine cylinder. Why?

The specific heat of combustion of pine wood is slightly higher than that of birch wood. Why is it more profitable to buy a cubic meter of birch firewood than pine firewood? (Let's consider the price of firewood to be the same)

What do you need to do to quickly cool an item by placing it in snow or crushed ice?

To what height could a 1 kg weight be lifted due to the energy released when cooling to 0 ° C in a glass of boiling water with a volume of 196 cm 3?

An electric lamp with a power of 60 W is lowered into a transparent calorimeter containing 600 g of water. In 5 minutes, the water warmed up by 4 ° C. What part of the energy consumed by the lamp did the calorimeter pass outside in the form of radiation?

Why do trees crackle in severe frosts?

Why are spaceships and rockets provided with a sheathing of their refractory metals?

Why is the dew more abundant after a hot day?

Why are boiling oil burns always worse than boiling water burns?

Compare the temperature of the water at the bottom of the falls with the temperature at the top. The height of the waterfall is 60m. consider that all the energy of the falling water goes to heating it.

A 75 W motor rotates the propeller blades inside the calorimeter, which contains 5 kg water for 5 min. Due to the friction of the propeller blades against the water, the water heats up. Assuming that all the heat released during friction went to heating the water, determine how many degrees it has heated up.

The 15 kW engine consumes 15 kg of oil per hour. Determine the efficiency of the machine.

Some installation, developing a power of 30 kW, is cooled by running water flowing through a spiral tube with a cross section of 1 cm 2. In a steady state, the running water heats up by 15 0 C. Determine the speed of the water flow, assuming that all the energy released during the operation of the installation goes to heating the water.

Why does steam burn more strongly than water of the same temperature?

What kind of firewood - birch, pine or aspen - emit more heat during complete combustion if they are all equally dried and their masses are equal? The specific heat of combustion of aspen is about 1.3 ∙ 10 7 J / kg.

Peat weighing 20 tons was burned in the boiler furnace of a steam engine. What mass of coal could replace the burnt peat? Specific heat of combustion of peat is assumed to be equal to 1.5 ∙ 10 7 J / kg.

How much oil needs to be burned in a thermal power plant in order to watch an hour and a half film on a 90-watt TV? Consider the efficiency of the power plant equal to 35%.

The combustion temperature of some chemical fuel in air at a normal pressure of 1500 K. What is the maximum possible efficiency of a heat engine using this fuel? The role of a refrigerator is played by ambient air with a temperature of 300K. find the engine power if the amount of heat 20 kJ is dissipated into the ambient air every second.

In the combustion chamber of an engine operating on a mixture of oxygen with hydrogen, hot water vapor is formed at a pressure of 8.32 · 10 7 Pa. The mass of water vapor is 180 g. The volume of the combustion chamber is 0.002 m 3. determine the maximum efficiency of such an engine if the temperature of the exhaust vapor is 1000K.

At the Kiev Research Institute of Experimental Design, a solar plant has been created to obtain hot water for the needs of agricultural complexes. The sun's rays heat the liquid circulating in the solar receiver, which transfers heat to the water supplied to the consumer. The daily productivity of the installation is 3 tons of water heated from 10º to 60ºC. How much firewood is saved for 1 month (30 days) of such an installation?

For 1 hour in the refrigerator, it turns into ice at a temperature of 0 0 C, a mass of water of 3.6 kg, which had an initial temperature of 20 0 C. What power is consumed by the refrigerator from the mains if it gives off 840 J / s energy to the surrounding space per unit of time?

On a winter road at a snow temperature of -10 0 C, the car skids for 1 minute 6 seconds, developing a power of 12 kW. how much snow will melt when the car is slipping, if we assume that all the energy released during slipping goes to heating and melting the ice.

Would we be able to observe, familiar to us, changes in nature in spring, if the specific heat of melting of ice were as small as that of mercury?

Why did the agronomist instruct the garden crops to be watered in the evening when they broadcast a message on the radio that there would be frosts at night? Explain the answer.

The water in the glass freezes when it cools down to 0 ° C. Why does water not freeze in some clouds, which are an accumulation of small droplets of water, even at lower temperatures (for example, at -5 ° C)?

What amount of snow at a temperature of 0 0 C will melt under the wheels of a car if it slips for 20 s, and 50% of all power goes to slip? The power of the car is 1.7 ∙ 10 4 W.

Determine how much coke is required to heat 1.5 tons of scrap iron from 20 ° C to the melting point. The efficiency of the melting furnace is 60%.

Why does water in reservoirs begin to freeze from the surface?

Why does cut grass dry faster in windy conditions than in calm weather?

When leaving the river after swimming, we feel cold. Why?

Why is a horse covered with a blanket in the cold, sweating after a ride?

Raw wood burns worse than dry wood. Why?

For 5 days, 5 ∙ 10 -2 kg of water has completely evaporated. How many molecules, on average, were ejected from the surface of the water in 1 second?

How to explain the appearance of frost on window panes in winter? Which side does it appear from?

How to explain the formation of a cloud trail behind a jet plane flying at high altitude?

What is the significance of the wetting phenomenon in the life of plants?

Geysers can be viewed as large underground reservoirs filled with groundwater and heated by the earth's heat. The exit from them to the surface of the Earth is carried out through a narrow channel, which in the "quiet" period is almost entirely filled with water. Assuming that the "active" period occurs when water boils in the underground reservoir, and that during the eruption the channel is filled only with steam, which is thrown out, estimate how much of the water is lost by the geyser reservoir during one eruption. The depth of the channel is 90 m, the heat of evaporation of water is 2.26 ∙ 10 6 J \ kg, the heat capacity of water is 4.2 ∙ 10 3 J \ (kg ∙ K)

Why internal combustion engines are not used in a submarine when diving

Does incomplete combustion of fuel in the internal combustion engine affect its efficiency; on the environment?

The car is moving at a speed of 72 km / h. The motor power is 600 kW, its efficiency is 30%. Determine the gas mileage for 1 km.

The temperature of the gases formed during the combustion of fuel in the cylinders of a car engine, 800 0 С; exhaust gas temperature 80 0 C. Fuel consumption per 100 km at a speed of 90 km / h is equal to 10 -2 m 3; heat of combustion of fuel 3.2 ∙ 10 10 J / m 3. What power could the engine develop if it were an ideal heat engine operating at the highest possible efficiency?

Due to imperfect thermal insulation, the refrigerator receives 420 kJ of heat from the air in the room in 1 hour. The temperature in the room is 20 0 С. What is the minimum power the refrigerator should consume from the mains in order to maintain the temperature inside the refrigerator -5 0 С?

The gas heating column consumes 1.2 m 3 of methane (CH 4) per hour. Find the temperature of the heated water if the outflowing jet has a velocity of 0.5 m / s. The diameter of the jet is 1 cm, the initial temperature of the water and gas is 11 0 C. The gas in the tube is under a pressure of 1.2 atm. Heater efficiency is 60%.

A person feels comfortable with a relative humidity of 40-60%. Why can there be a feeling of exhausting heat at an air temperature of 25 ° C and a relative humidity of 80-90%, while at a temperature of 30 ° C and a humidity of 30%, the state of health can be good?

At sea, at an air temperature of 25 ° C, the relative humidity is 95%. At what temperature can fog be expected?

It is snowing outside. How to determine the percentage of water in it?

Above the sea surface at a temperature of 25 0 С the relative air humidity was equal to 95%. At what temperature can fog be expected?

At what air temperature is its relative humidity equal to 50%, if it is known that the water vapor contained in the air passes into the saturation state at 7 0 С?

In the evening, when the air temperature is 2 0 С, the relative humidity is 60%. Will there be frost at night if the air temperature drops to -3 0 С; up to -4 0 С; up to -5 0 С?

Which air is lighter - dry or humid at the same pressure?

In the capillaries of sandy soils at a temperature of 20 ° C, water rises to a height of 1.5 m. What is the diameter of the soil capillaries? Wetting is considered complete .

In drought, packed soil dries out strongly, and plowed soil weakly. Why?

In one breath, air of 0.5 liters enters the lungs of a person. How many oxygen molecules are there in such a volume of air if the proportion of oxygen in it is 20%?

How much oil does a thermal power plant need to burn in order to watch a 1.5 hour movie on a 250 W TV? Power plant efficiency 35%

Electricity and magnetism

Is the lightning between the cloud and the Earth an electric shock; between the clouds?

How does an electric field “fight” dust?

Why are flammable objects, such as powder depots, sometimes covered with a metal grounded mesh?

How to Protect Lab Workers Experimenting with Large electrostatic charges, from the action of the electric field of these charges?

If any conducting body, including a human, is isolated from the ground, then it can be charged to a high potential. So, with the help of an electrostatic machine, the human body can be charged to a potential of tens of thousands of volts. Does the electric charge placed in this case on the human body have an effect on the nervous system?

Which three fish are often called living power plants? How great is the tension they create?

Franklin said that with a discharge of electricity from a battery, he could not kill a wet rat, while a dry rat instantly died from the same discharge. What caused this?

What changes does the current in the human body cause?

Why is the accidental passage of current through two closely spaced points of the body, for example, two fingers of the same hand, felt not only by these fingers, but also by the entire nervous system?

Why is it dangerous to touch high-voltage masts, because the wires with current are separated from the masts by whole strings of insulators?

Lightning most often strikes trees with roots that penetrate deep into the soil. Why?

Centuries of experience have shown that lightning most often strikes tall deciduous trees, mainly standing alone. Therefore, such trees are a good conductor for atmospheric electricity. Why is a person caught in a thunderstorm warned not to hide under the trees? Why does a lightning rod divert lightning from a person, and a tree, on the contrary, attracts to him?

There are times when a bird sitting on a power line wire is electrocuted. Under what circumstances can this happen?

The writer B. Zhitkov describes the following case: “Once, at the beginning of summer, I rode on horseback on the floodplain of the river. The sky was covered with clouds, a thunderstorm was gathering. And suddenly I saw that the tips of the horse's ears began to glow. Now above them formed like bundles of bluish fire with indistinct outlines. These lights seemed to be streaming. Then jets of light ran over the horse's mane and over its head. All this lasted no more than a minute. Rain poured down and the amazing lights disappeared. " Explain this natural phenomenon.

As a rule, street dust, rising in the air, is charged positively. What electrical charge should the paint have to prevent dust from settling on the walls of buildings?

Draw a table in a notebook: Write down what types of energy are used to generate electric current during operation: a battery, a photocell, a thermal power plant, a hydroelectric power station, a thermoelement, a solar battery, a galvanic cell, a wind turbine.

Mechanical	Internal	Chemical	Luminous

1. Is it possible to replace a blown fuse with a thick wire or a bundle of copper wires ("bug")? Why?

   A wind turbine is installed on the school building, which rotates the shaft of an electric generator with a capacity of 0.6 kW. How many 12 V, 2A lamps can this wind farm power?

   The bike-mounted power supply generates current for two lamps, each lamp being 0.28A at 6V. Determine the power of the generator and the work of the current for 2 hours.

   Why does energy consumption increase when working on a lathe or drilling machine with an incorrectly sharpened or blunt tool?

   Two trolleybuses with the same electric motors move simultaneously, one at a higher speed, the other at a lower speed. Which of them has a greater work of electric current, if we assume that the resistance to movement and the time of movement are the same in both cases?

   A wind turbine is installed in the mountain village, which drives an 8 kW electric generator. How many 40 W bulbs can be powered from this source if 5% of the power is consumed in the lead wires?

   To what value is it necessary to increase the voltage in the power transmission line with a resistance of 36 ohms so that 95% of the electricity is transmitted from a power plant with a capacity of 5 MW?

   With what cross-section is it necessary to take a conductor for the construction of a power transmission line from a power plant to a consumer with a total length of 4 km in order to transmit a current of 10 kW to the consumer? Line voltage 300 V, allowable transmission loss 8%

   A power of 62 kW is transmitted from the substation to the consumer. Line resistance 5 ohms. For cases of transmission at a voltage of 620 V and 6200 V, determine: what power the consumer will receive; consumer voltage.

   At the ends of a two-wire power transmission line 175 meters long, the power of alternating current is 24 kW at a voltage of 220V. Calculate the power loss in this line if it is made of copper wire with a cross-sectional area of ​​35 mm 2.

   What are the causes of power loss in a transformer?

   Why is a massive chain attached to the body of a gasoline tanker, several links of which drag along the ground?

   Suggest a project of an installation that allows collecting dust and smoke with the help of an electric field.

   Why should the lower end of the lightning rod be buried deeper, where the layers of the earth are always wet?

   Why can birds sit safely on high voltage power lines?

   Why is it possible for a person to be electrocuted in damp rooms even if he touches the glass cylinder of an electric light bulb?

   Why, in the event of a fire in electrical installations, do you need to immediately turn off the switch?

   Why is it impossible to extinguish fire caused by electric shock, water or a conventional fire extinguisher, but rather use dry sand or sandblast extinguisher?

   What effect of electric current do we face when ozone is formed in the air during lightning discharges?

   Why is it advisable to stand on one leg near where the broken high voltage wire touches the ground?

   In one of his works, the famous Russian writer V.K. Arseniev describes the behavior of ball lightning slowly floating through the air in the following way: "... the ball avoids contact with tree branches in every possible way, bypasses every twig, every twig or blade of grass." Explain the reasons for this movement.

   To clean the air from dust in some industries, electrostatic filters are used. These filters create a highly non-uniform field. Are all dust particles attracted to the electrode with the highest field strength?

   Lightning observed in nature is characterized by the following average values: current strength 15 kA, potential difference (between two clouds or a cloud and the Earth) 10 5 V, duration 0.02 sec. The number of lightning strikes around the globe on average reaches 100 lightning strikes per second. Using these data, estimate the average power of one lightning and all lightning together. Compare the latter value with the capacity of the Krasnoyarsk hydroelectric power station - one of the world's largest power plants of 5 ∙ 10 6 kW.

   What electrical capacity does the Earth have? The radius of the Earth is 6400 km.

   Why is the screen of a working TV covered with more dust than all other bodies in the room?

   Why can fuses in the lighting network sometimes melt near the place of a lightning strike and damage sensitive electrical measuring instruments?

   Why do electric incandescent lamps most often burn out when turned on and very rarely when turned off?

   In the essay of the French physicist Arago "Thunder and Lightning", there are many cases of magnetization of the compass needle, magnetization of steel objects by the action of lightning. How can these phenomena be explained?

   Due to a short circuit, the wires caught fire. Why can't they be extinguished with water or a fire extinguisher until the area that has caught fire is disconnected from the mains?

   Why on electrified railways is the positive pole of the voltage source connected to the overhead wire, and the negative pole to the rails?

   How much electricity needs to be spent to obtain 2.5 liters of hydrogen from water at a temperature of 25 0 C and a pressure of 10 5 Pa, if the electrolysis is carried out at a voltage of 5 V, and the efficiency of the installation is 75%?

   Why are wires of as large a diameter as possible used to reduce corona power losses in high voltage power lines? Why does the loss of electrical energy for corona discharge increase sharply in bad weather - heavy fogs, rains and snowfalls?

   How many times does the energy loss in the power transmission line decrease when the voltage rises 50 times?

   How can a superconducting solenoid winding accident be avoided?

   Why does the presence of a very high voltage in the secondary winding of the step-up transformer not lead to large energy losses in the winding itself?

   Why does the power consumption increase with increasing load (decreasing resistance) in the secondary circuit of the transformer?

   On what frequency do ships transmit the SOS distress signal if, according to international agreement, the wavelength should be 600m?

   How can you protect people from the harmful effects of external electric fields?

   What human organs create a magnetic field around them?

   As you know, bats are guided in space by means of ultrasound. What kind of animals do you know that would orient themselves in space using electromagnetic waves?

Optics.

What effect of light causes the formation of chlorophyll in plant leaves, tanning of the human body and darkening of photographic film?

Give an example of the chemical effect of light on the physical body.

Give an example showing that bodies exposed to light heat up.

Name the effects of light on physical bodies known to you.

Why should students in classrooms sit with the windows on the left?

On a sunny day, the length of the shadow on the ground from a fir tree 1.8 m high is 90 cm, and from a birch - 10 m. What is the height of the birch?

Why you can look calmly at fluorescent lamps: they do not "hurt" your eyes?

It is dangerous to photograph a tiger from a distance of less than 20 meters. What size can a pinhole camera with a 1mm hole be so that a tiger is striped in a photograph? The distance between the stripes on the tiger skin is 20 cm.

To observe sea animals, a window was made in the bottom of the vessel, the diameter of which is 40 cm, which is much larger than the thickness of the glass. Determine the viewing area of ​​the bottom from this porthole, if the distance from it to the bottom is 5m. the refractive index of water is 1.4.

The illumination of the workplace for jewelry work, according to the standards, should be at least 100 lux. At what minimum height from the workplace should a 100 cd lamp be placed?

What harm can water droplets fall on plant leaves on a sunny day?

The lens is sometimes referred to as a "fire glass". To which lenses, such a name cannot be applied? Why?

In the early morning the Sun, reflected from the surface of calm water, blinds the eyes, and at noon you can look at the image of the Sun in the water even without dark glasses. Why?

Why are dragonfly wings rainbow colored?

Explain the reasons for the appearance of a double rainbow. What is the alternation of colors in the first (main) and second rainbow?

In hot deserts, a mirage is sometimes observed: in the distance, the surface of the reservoir "appears". What physical phenomena caused such a mirage?

The sensitivity of the retina to yellow light with a wavelength of 600 nm is 1.7 · 10 -18 W. How many photons must hit the retina every second for light to be received?

The higher the voltage applied to the X-ray tube, the harder (i.e., shorter wavelengths) the rays it emits. Why? Will the hardness of the radiation change if, without changing the anode voltage, the filament of the cathode is changed?

If you look from the shore at a fish swimming in the river, then often, even knowing this fish, you can make a mistake in its name. In particular, mistakes are frequent when the fish is wide and flat: its vertical dimensions are somewhat reduced, while the horizontal ones remain unchanged. For example, bream does not seem so flat in the water and can easily be mistaken for another fish. How do you explain this?

Explain from the point of view of optics the expression "At night all cats are gray"

Why, if you dive under water, all objects appear blurry with indistinct contours, and very small objects are not visible at all?

There are organisms (for example, the larva of a feathery mosquito), which are not visible in the water due to their transparency. But the eyes of such invisible creatures are clearly visible in the form of black dots. Why are these creatures not visible in the water? Why are the eyes at the bottom not transparent? Will they remain invisible in the clear air?

A curious four-eyed fish lives in the coastal waters of North and South America. Each of her eyes is divided into two halves - two pupils, but one lens. Why does a fish need such an eye structure?

Pupils in horses are located horizontally, while in cats and foxes, on the contrary, they are located vertically. Explain why?

As you know, with the onset of darkness, chickens completely cease to see, and owls, on the contrary, can use their eyesight only from that moment - they do not see anything during the day. Do you know what explains the peculiarities of vision of these birds.

Is it correct to say that a hare, without turning its head, sees objects from behind?

Why can a falcon see at a great distance?

Why are most of the inhabitants of the Far North white, and those whose color is different, for example a squirrel, a hare, change it to white in winter?

Why are insects living in the polar regions and high mountain regions predominantly dark in color?

In the dense spruce forest there are no red, blue or yellow flowers, only white or pale pink. How can this be explained?

What color of fish helps them to disguise themselves from enemies?

Nuclear physics.

Why is natural uranium not an atomic fuel, and its storage is not associated with an explosion hazard?

Why are radioactive drugs stored in closed, thick-walled containers? In lead containers?

Deposits of radioactive elements are always accompanied by lead. It is known that the thorium series ends with the lead isotope 208 Pb (232 Th → 208 Pb). Assuming the age of thorium ore to be 4 · 10 9 years (on the order of the age of the solar system), determine the mass of lead that appeared in this ore from thorium weighing 1 kg.

The submarine "Nautilus" (USA) has a fuel capacity of 14.7 MW, an efficiency of 25%. The fuel is enriched uranium weighing 1 kg, the fission of which releases an energy of 6.9 · 10 13 J. Determine the fuel supply required for the annual navigation of the boat.

The average absorbed dose of radiation by an employee working with an X-ray unit is 7 μGy per hour. Is it dangerous for an employee to work for 200 days a year, 6 hours a day, if the maximum permissible radiation dose is 50 mGy per year?

Why is natural uranium not an atomic fuel and its storage is not associated with an explosion hazard?

The explosion of an atomic bomb (M = 1 kg of plutonium 242 Pu) produces one radioactive particle for each plutonium atom. Assuming that the winds evenly mix these particles in the atmosphere, calculate the number of radioactive particles falling into a volume of 1 dm 3 of air at the Earth's surface. The radius of the Earth is assumed to be 6 ∙ 10 6 m.

BIBLIOGRAPHY.

L.A. Kirik. Mechanics. Pressure of liquids and gases. 7th grade. Independent and control work. Ilexa. Gymnasium. Moscow-Kharkov. 1998

L.A. Kirik. MKT. Properties of gases. Thermodynamics. Vapors, liquids and solids. Grade 10. Ilex's independent and control work. Gymnasium. Moscow-Kharkov. 1998

L.A. Kirik. Electricity and magnetism. Grades 10 - 11. Ilex's independent and control work. Gymnasium. Moscow-Kharkov. 1998

L.E. Gendenstein; L.A. Kirik. THEM. Gelfgat. Solutions to key problems in physics for basic school. Ilexa. Moscow. 2005

V.I. Lukashik. Physics Olympiad. Moscow. Education. 1987.

I.Sh. Slobodetsky, V.A. Orlov. All-Union Physics Olympiads. Moscow. Education. 1982

3800 problems for schoolchildren and university applicants. Moscow. Bustard. 2000

I.M. Varikash., B.A. Kimbar, V.M. Varikash. Physics in nature. " People's Asvet ". Minsk., 1967

A.V. Peryshkin. Collection of problems in physics for the textbooks of AV Peryshkin "Physics - 7,8,9". Moscow. Exam. 2006.

IN AND. Lukashik, E.V. Ivanova. Collection of problems in physics 7-9 grades. Moscow. Education, 2005

Answers and solutions.

Dear colleagues! In this section, in addition to answers and solutions to problems, you will undoubtedly find many interesting facts that will help you in your future work.

Mechanics.

4. People have long tried to understand why dolphins and whales swim quickly, but only recently it was possible to establish that the speed of these animals depends on the shape of their bodies. With this in mind, the shipbuilders built an ocean-going ship not of a knife-like shape, which all modern ships have, but of a cetacean. The new vessel turned out to be more economical, its engine power is 25% less, and the speed and carrying capacity are the same as those of conventional ships. In addition, the speed of movement of these animals depends on the structure of their skin. Its upper layer, very thick and elastic, is connected with another layer of the skin, in which there are processes. These processes enter the cells of the upper layer, and the dolphin's skin becomes even more elastic. With a sharp increase in speed, “speed folds” appear on the dolphin's skin and the laminar flow (flow in layers) does not turn into turbulent (disordered). The running wave on the dolphin's skin dampens the turbulence.

5. The oncoming water acts on individual fish in such a way that the movement of each of them can be facilitated or impeded, depending on the position in relation to the school. This factor determines the drop-shaped form of a moving school of fish, in which the resistance of water to the movement of the school is the least.

6. Among animals, devices are very common, due to which friction is obtained small when moving in one direction and large when moving in the opposite direction. The bristles of the earthworm, freely passing the body forward and strongly inhibiting the reverse movement, make it possible for the worm to crawl. With lengthening of the body, the head part moves forward, and the tail part remains in place; during contraction, the head part is delayed, and the tail is pulled towards it.

7. The strongest bird flies in front. The air flows around her body like water does the bow and keel of a ship. This flow explains the sharp corner of the jamb. Within a given angle, the birds move forward, they instinctively guess the minimum of resistance and feel if each of them is in the correct position relative to the leading bird. The arrangement of birds in a chain, in addition, is explained by another important reason. The flapping of the wings of the front bird creates an air wave, which carries some energy and facilitates the movement of the wings of the weakest birds, which usually fly from behind. Thus, birds flying in a school or in a chain are interconnected by an air wave and the work of their wings is performed in resonance. This is confirmed by the fact that if you connect the ends of the birds' wings at a certain point in time with an imaginary line, you get a sinusoid.

8. To move forward quickly, you need to throw back a lot of water, so swimming limbs are almost always wide and flat in shape. When the foot moves forward, the membrane bends and the foot feels little resistance; when the foot moves backward, the animal rakes in a sufficient amount of water and moves forward itself quickly.

9. Foliage significantly increases the frontal surface of the tree, and in connection with this, the effective wind force also increases.

10. An ear of oats takes a position in which it offers the least resistance to the wind, the ears turn in the direction of the wind and turn to it with their bases.

11. The tiny green sprout experiences the greatest resistance near the soil crust. To pierce its sprout, it develops an effort equal to 0.25 kg.

12. The body acquires a greater store of energy if the force applied to it acts for a long time or at a sufficiently large distance, for example, a run-up before a jump, a swing before a blow. The muscles of the grasshopper cannot develop great efforts, therefore, the long limbs of the grasshopper serve to increase the jumping range, which requires a significant accumulation of energy.

13. When the arm is extended, the direction of action of the muscle force makes a small angle with the longitudinal axis of the lever. In order to keep the same load in this case as with a bent arm, it is necessary to significantly increase the muscle effort. With one and the same muscular effort, an extended arm can hold a much smaller load.

14. By shifting the nut towards the molars, we reduce the lever arm in relation to the transverse axis around which the mandible rotates. Thus, the moment of the resistance force becomes less than the moment of rotation of the force of the muscles that lift the lower jaw (temporal, chewing, etc.)

15. An inverted turtle is like a heavy spherical segment lying on a convex surface. Such a segment is very stable and in order to turn it over, you need to raise its center of gravity high enough. Many turtles cannot raise their center of gravity high enough to roll over and, therefore, die upside down.

16. The tree's center of gravity is slightly higher in summer when the trees are full of leaves. Therefore, deciduous trees are less stable than in late autumn or winter, and summer winds often break them or uproot.

17. In the shade of the forest, the lower branches of the trees die off and the crown is at the top. The tree's center of gravity also shifts upward, making it less stable. A tree growing in an open area has a crown lower. The center of gravity of such a tree lies closer to the roots, and it better withstands the pressure of the wind.

18. Spruce grows in moist soil, and its roots find sufficient moisture near the surface. They run widely around the tree, but do not penetrate deeply. A pine tree growing in dry places is forced to seek water at great depths. Its roots go very deep into the ground, so it is more stable.

19. The wasp sticks a sting with a force of only 1 mg, but its sting is very sharp, the area of ​​its tip is 0,000,000,000,003 cm 2. therefore, the wasp can create tremendous pressure.

20. When a homogeneous body is compressed, the amount of deformation at all its points will be the same, with the exception of the ends where the body rests on other bodies. The fact is that the deformable body does not come into contact with the support and other bodies at all of its points; therefore, the pressure at the ends of the deformable body will be greater than inside it. In order for the pressure to be about at all points the same, its ends must have a large cross-sectional area. This explains the presence of thickening on some bones of the skeleton of humans and animals.

21. A beaver's tooth consists of several layers of different hardness. When a beaver gnaws wood, the strong enamel covering the upper part of the tooth is under greater stress, while the rest of the relatively soft tissue is less stressed. As a result, the entire tooth is grinded evenly and the taper angle remains unchanged. Self-sharpening tools work on this principle.

22. The weight of a whale reaches 90-100 tons. In water, this weight is partially balanced by the buoyancy force. On land, under the influence of a huge weight, a whale's blood vessels are compressed, breathing stops, and it dies.

23. At great depths of the sea, there is a large hydrostatic pressure, which is balanced by the internal pressure in the body of the fish. If the fish is on the surface of the sea, then the pressure in the body will not be balanced by external pressure, so the fish swells, its internal organs burst and the fish dies.

24. The diver does not experience this pressure because he breathes the air supplied to the diving suit, and the air pressure on his body from the outside is balanced by the air pressure from the inside.

25. During the lowering of the diver into the water or raising from it, the balance between the external pressure and the pressure in the organs of the diver's body is disturbed. In addition, with a sharp rise from the water to the surface, the external pressure drops rapidly, gases dissolved in body fluids begin to rapidly evolve, leading to blockage of small blood vessels by air bubbles. To avoid this, divers in rubber diving suits usually descend to a depth of no more than 50 m, and their ascent is done slowly.

26. In the chest cavity of a person immersed in water with a tube, in his lungs and on the surface of the heart, outside air pressure prevails. On the surface of the body, hydrostatic pressure additionally acts, depending on the depth of immersion. Therefore, even at a shallow depth, such a force will act on the chest that the muscles will not be able to overcome it and expand the lungs for inhalation. Hydrostatic pressure also impedes blood circulation. Bleeding from the ears is explained by the fact that under the action of excessive hydrostatic pressure, blood enters the tympanic cavity, where there is a lower pressure than on the surface of the body. The elephant has very strong muscles, so even a long stay under water does not harm it.

27. The elephant's neck is short, and he cannot bend his head to the water, as other animals do. The elephant lowers its trunk into the water and draws in air. In this case, due to external atmospheric pressure, water enters the trunk. When the trunk is filled with water, the elephant bends it and pours the water into its mouth.

28. Any gas tends to move from a place where there is a greater pressure, to an adjacent space, where the pressure is lower. In the blood of fish, the oxygen pressure is less than its pressure in the water, so oxygen passes from the water to the blood. Flowing through the blood capillaries of the gills.

29. The air we breathe contains 21% oxygen. It was found that oxygen dissolves in water twice as much as nitrogen, which leads to the enrichment of air with oxygen: air dissolved in water contains about 34% oxygen.

30. Fish breathe oxygen dissolved in water. When there is little oxygen in the water, they rise to the surface that comes into contact with the air, where there is more oxygen.

31. Underwater plants do not need solid stems as they are supported by the buoyancy of the water. In addition, if such plants had a hard stem, then the water during the waves could break them.

32. For each square centimeter, forces of approximately 1 kN act, and the total force acting on the surface of the whole body will be approximately equal to 20,000 kN.

34. Everyone knows Guericke's experience with the hemispheres. In this experience, obviously, nothing would have changed if the hemispheres were nested one into the other. In the absence of air between the walls of the hemispheres, it would also be impossible to separate them. Similar to such nested hemispheres are the hip joints, which connect the lower limbs to the pelvis. Due to the absence of air between the mirror-smooth surfaces, atmospheric pressure firmly presses the joints together. In order to separate them, as in the experiment with the Magdeburg hemispheres, considerable force must be applied.

35. Atmospheric pressure contributes to a tighter fit of the joints to each other. With a decrease in pressure when climbing high mountains, the connection between the bones in the joints decreases, as a result, the limbs do not obey well, dislocations are easily obtained.

36. So that the pressure on the eardrum from the inside becomes equal to the pressure outside.

37. A modified fin adhered to the back of the fish and turned into a suction cup. The action of this suction cup is similar to that of a toy pistol firing a rubber-tipped stick. When the stick hits the wall with the rubber tip, the rubber flattens, and then, thanks to the elastic forces, it takes on a concave shape again. A rarefied space is formed between the wall and the rubber suction cup, since part of the air was displaced from there during the impact. Therefore, under the influence of atmospheric pressure, the stick firmly "sticks" to the wall. The action of the fish sticking is carried out by the contraction of the fish muscles. Suction cups are extremely common in the animal kingdom. For example, cuttlefish and octopuses have a row of tentacles with numerous suction cups that attach them to various objects.

38. No, it cannot. When moving over the ceiling, the fly is held back by atmospheric pressure. It has small suction cups at the ends of its legs.

39. Due to atmospheric pressure.

40. When the horse pulls the legs out of the viscous soil under the hooves, a reduced pressure is created and external atmospheric pressure makes it difficult for the legs to move. In cloven-hoofed animals, when pressing on the soil, the hooves bifurcate, and when the legs are pulled out, they come closer and air passes freely around them.

41. Diving to greater depths, we displace a larger volume of water. According to Archimedes' law, in this case, a large buoyant force will act on us.

42. In horses and other animals, the nostrils are located at the highest point of the body, and therefore, even without moving their legs, they do not choke.

43. The swim bladder is a kind of device that regulates the specific gravity of the fish when it moves to a particular depth. With the help of the swim bladder, the fish keep their balance in the water. Going deeper, the fish keeps the volume of the swim bladder constant. It maintains a pressure in it equal to the pressure of the surrounding water, for which it continuously pumps oxygen from the blood into the bubble. On the ascent, on the contrary, the blood intensively absorbs oxygen from the swim bladder. Such pumping and absorption are rather slow, therefore, when the fish is quickly pulled out from a great depth, oxygen does not have time to dissolve in the blood and the inflating bubble ruptures the fish. For this purpose, conger eels have a safety valve: when they ascend quickly, it opens and releases gas from the bubble.

44. In water, due to the action of the buoyancy force, the sinking has a low weight.

45. a thick layer of down and feathers that covers the body of a waterfowl, does not allow water to pass through and contains a significant amount of air. Due to this, the body of a bird in the water has a low specific gravity and does not sink deep into the water.

46. ​​Thanks to the wings, the seeds are picked up by the wind and carried over long distances.

47. When clarifying this phenomenon, it was found that in the calm, soaring birds stay somewhat behind the vessel, and in the wind - closer to the leeward side. It was also noticed that if a bird lagged behind the ship, for example, when hunting for fish, then, catching up with the steamer, for the most part it had to vigorously flap its wings. All these mysteries have a simple explanation: over the steamer, from the operation of machines, streams of rising warm air are formed, which perfectly keep the birds at a certain height. Birds unmistakably choose a location relative to the ship and the wind where the updrafts from steam engines are greatest. This enables the bird to travel using the power of the steamer.

47. It has been established that the limbs act like a hydraulic drive, the fluid for which compresses blood.

49. During the wind, the air jets carrying snow do not bypass the bush, but penetrate it. When streams flow around individual stems, local eddies arise, the pressure decreases and snow particles are drawn into the bush. In winter, a snowdrift protects the bush from freezing, and in spring the plant receives more moisture.

50. The bird does not rise up an inclined line or vertically, it takes off only in a spiral, therefore, once it gets into the well, it cannot fly out of it.

51. No matter how the cat falls, it always stands on 4 legs. This is due to the angular momentum. The falling cat presses its paws and tail to itself, thereby accelerating the rotation. As soon as she takes the position with her paws down, she withdraws her limbs, rotation stops and the cat falls on its paws.

52. This is explained by the fact that the human body has a number of cavities containing air, for example, the intestines, middle ear, frontal and maxillary cavities of the bone. The air pressure in these cavities is equal to atmospheric pressure. When the external pressure on the human body quickly decreases, the air inside us begins to expand, exerts pressure on various organs and causes pain.

53. An example of the use of atmospheric pressure in human life is a breathing apparatus. The chest cavity is separated from the abdominal by a convex septum - the diaphragm. With the contraction of the respiratory muscles of the chest and the muscles of the diaphragm, the volume of the chest increases, the air in the lungs expands, and the pressure drops. At this time, under the influence of atmospheric pressure, outside air enters the lungs - inhalation occurs. On the contrary, with the contraction of the respiratory muscles of the chest, its volume decreases, the air in the lungs is compressed, its pressure becomes higher than atmospheric, and exhalation occurs. The breathing apparatus works on the principle of a suction pump.

55.20 km; 0.000075 mm 2

56. Bending is always accompanied by stretching of the material along the convex side and compression along the outside. The middle part of the object does not experience any noticeable deformation. The peculiarity of the tubular stem of cereal plants is that it is strong enough, and very little material was used for it, so that the plant could develop and grow in the shortest possible time.

57. Note: First you need to determine the mass of the glass. Then fill it with water and put it back on the balance. The density and mass of the vodzha in a glass determine its capacity. Having filled a glass with an unknown liquid, the mass is determined on the scales. Knowing the mass of the liquid in the glass and its volume, the density of the liquid is calculated.

58.5.5 kg. Taking into account that 0.1 cm 3 = 100mm 3, from the proportion

, we find that a cloud with a volume of 1 m 3 contains 14 ∙ 10 8 droplets. Their volume will be equal to V = 4 ∙ 10 -6 ∙ 14 ∙ 10 0 = 56 ∙ 10 2 (mm 3), or 5.6 cm 3. hence the mass of water in a cloud with a volume of 1 cm 3 = 1
= 5.6 g

59. Law of Inertia .

60. In case of a sudden change in the direction of the fox's movement, the dog cannot follow it, since by inertia the dog will move in the initial direction for some time.

61. With a sharp pulling out of the plant, its roots do not have time to move and the stem breaks off. The roots of the weeds remaining in the soil germinate quickly again.

62. Ripe pods of leguminous plants, quickly opening, describe arcs. At this time, the seeds, breaking away from the attachment points, move tangentially to the sides by inertia.

63. Elastic hairs on the soles of the hare's feet lengthen the braking time when jumping and therefore weaken the impact force.

65. In the body of an animal, strength is created by muscles. Consequently, the greater the muscle strength and the less its mass, the greater the mobility of the animal (
). The force exerted by a muscle is directly proportional to the cross-sectional area of ​​the muscle's incision. Therefore, with a decrease in muscle in n times the strength decreases in n 2 once, while the weight of the muscle, depending on its volume, decreases by about n 3 once. Thus, with a decrease in the size of the animal's body, its strength decreases more slowly than its weight.

66. The weight of an animal is directly proportional to the cube of its linear dimensions, and the surface is proportional to the square of its linear dimensions. Consequently, with a decrease in the size of the body, its volume decreases much faster than the surface. Resistance to movement in air depends on the surface of the falling body. Therefore, small animals experience more resistance than large ones, since they have a large surface per unit of weight. In addition, when a body of small volume hits an obstacle, then all its parts stop moving at once, and during the impact they do not press against each other. When a large animal falls, the lower parts of its body stop their movement upon impact, while the upper ones still continue to move and exert strong pressure on the lower ones. This is the concussion that is fatal to large animals.

67. These animals in the process of movement throw water back, and themselves, according to Newton's third law, move forward. A swimming leech drives the water back with undulating bends of the body, a swimming fish - with waves of its tail.

68. Squirrel makes big jumps from tree to tree. The tail helps her: it serves as a kind of stabilizer. The fox's tail helps it make sharp turns when running fast. This is a kind of air rudder.

69. The pointed shape of the pike's head experiences little water resistance, so the pike swims very quickly.

70. To reduce resistance to movement.

71. There is little friction of the fish against the hands, so it slips out of the hands.

76.540l; ≈0.7 kg.

82.5.5 kmph. Let us denote the speed of the motor ship in motionless water relative to the coast through v 1, and the speed of the river flow through v. Then the speed of the motor ship downstream will be v 1 + v against the current v 1 -v. From the condition of the problem v 1 + v = 600 km \ day, and v 1 -v = 336 km \ day. The joint solution of these equations gives a value of 5.5 km / h

84. No. The mass of the fox is more, so the speed is less. The distance will increase.

88.1.11 * 10 8 Pa; 0.26 ∙ 10 6 Pa.

92. The bottom of the vessels is held by the force of water pressure from below, and disappears when this force is equal to the force of pressure on the bottom of the vessel from above. The pressure of a liquid depends on its density. ρ rt ρ in, then the bottom of the vessel will disappear.

93. When we drink, we create an area of ​​reduced air pressure under the lips above the surface of the water. Due to atmospheric pressure, water rushes into this area and enters our mouth.

99. Water will go down and will not close the access of air necessary for combustion to kerosene.

104. ≈11 million kW

105.5 ∙ 10 4 kW

108.4 ∙ 10 10 J

111. N floor =

114. Elastic longitudinal waves, both caused by other marine life and waves reflected from obstacles, caused by the fish's own movement.

116. The elastic surface of the wave propagates in the earth's crust. It is possible to register not only the fact itself, but also the location of the test using several sensors installed at different points.

117. The sound from the explosion of the projectile will reach a person later than the blast wave, since the speed of the blast wave is much greater than the speed of sound.

118. To roughly determine the direction of sound waves

By the phase difference of the oscillations and the sound wave.

119. The wings of a loaded bee emit a sound of a lower tone than an unloaded bee.

120. The frequency of oscillation created by the wings of a bird is below our hearing threshold, so the bird sings like a sound we do not perceive.

121. In the forest, the ear perceives sounds that came not only directly from their source, but also those that came from the side, reflected from the trees. These reflected sounds make it difficult to determine the correct direction to the sounding object.

122. The noise arises because the air jets, bending around the branches and needles of the needles, form small vortices behind them, emitting a faint hissing sound. Merging together, these faint sounds form the strong noise of the forest.

124. Some birds are attracted to airports by the high-pitched sounds of turbines that vibrate at frequencies and wavelengths similar to those produced by many animals.

126.

127. Bats make a variety of sounds, but almost all of them fall into the frequency range that lies above the human hearing threshold. During the flight, the bat continuously irradiates the space in front of it with ultrasonic pulses. If an obstacle is encountered on the path of the ultrasonic wave, then a reflection appears from it - an echo that is perceived by the animal. With the help of echo, bats detect small moving objects that are inaccessible to their eyes. They use echoes not only for orientation, but also for finding food for themselves. Echo sounders and various kinds of flaw detectors work on the principle of an ultrasonic mouse locator.

128. Hair absorbs the ultrasound emitted by the bat, so the mouse, not perceiving the reflected waves, does not feel obstacles and flies directly at the head.

129. It turned out that some butterflies have a special organ in the abdominal cavity that warns them about the approach of a bat. When a mouse flies out to hunt at nightfall, these butterflies instantly pick up ultrasonic impulses, and, making a sharp turn, glide to the ground to get out of the predators' irradiation field.

130. The frog's spherical bubbles, inflating when screaming, are a kind of resonators. They serve to amplify the sound.

131. Due to the mobility of the auricles, animals are able to establish the direction in which the sound source is located.

132. At the moment of danger, the roundhead lizard stands on its tail, begins to vibrate and as a result quickly sinks into the ground.

133. to the frequency.

134.17m and 1.7 ∙ 10 -4m

137.
... There are more molecules in a glass of mercury.

Molecular physics.

143. Due to diffusion, the protective substance is absorbed over time by the volume occupied by water.

146. Flowers contain aromatic substances, the molecules of which diffuse into the air.

147. Plants trap a significant part of the sun's rays, so the soil under them during the day heats up less than the bare soil under them. At night, when the air temperature drops significantly, plants protect the soil from intense radiation and it does not cool down as much as bare soil.

148. The water temperature in severe frost is much higher than the ambient temperature, so the bird will be cooled less in the water than in the air.

149. Yes, because his breathing and blood circulation almost stop.

150. In the hot part of the day, the sand in deserts heats up so much that even at a height of 5 cm from its surface the temperature is several degrees lower.

151. The heaviest, coldest air flows into low places during frost.

152. Both in the wind and in a calm, the thermometer readings will be the same, since the air temperature is the same, but a person is warmer in a calm because the layer of air adjacent to our body is heated by its heat and protects from further cooling. In the wind, such a layer cannot be held, and cold air flows around the skin all the time, cooling it strongly.

153. These animals have a subcutaneous fat layer that prevents rapid heat loss (since fat is a poor conductor of heat).

154. It turns out that the deer has inflatable wool, the hollow hairs are filled with air. Since the air does not conduct heat well, such wool protects the deer well from the cold.

155. Heat loss occurs always from the surface. The body's heat storage is proportional to the volume of the body. With a decrease in body size, the surface decreases more slowly than the volume, therefore small organisms are less "economical" in keeping warm than large ones.

156. Snow cover protects raspberries from freezing.

157. Snow is a poor conductor of heat, so the snow cover during severe frosts and blizzards protects birds from freezing.

158. This is explained by the fact that foxes' ears are organs that remove heat from the body. Since it is necessary to reduce heat transfer in the north, in the process of biological selection, foxes with small ears have most adapted to life in the far north.

162. So that the seeds do not freeze.

163. Ice conducts heat approximately 20 times better than snow, so plants freeze under the ice crust.

164. During flight, the plumage of a bird is compressed and contains little air, and as a result of its rapid movement in cold air, an increased heat transfer to the surrounding space occurs. This heat loss is so great that the bird freezes on the fly.

165. Coagulating, animals significantly reduce the outer surface of the body, which leads to a decrease in heat transfer.

169. In a snowless winter, plants can freeze out. The snow cover does not conduct heat well and therefore contributes to the maintenance of a higher temperature in the soil.

170. A thicker hairline of animals reduces the transfer of heat to the surrounding space, which is especially important in the Far North.

172. During flight, the plumage of a bird is compressed and contains little air, and as a result of rapid movement in cold air, an increased heat transfer to the surrounding space occurs. This heat loss is so great that the bird freezes on the fly.

173. Spring frosts are most dangerous for plants planted on dark soils, since they have more heat radiation than light ones, and, therefore, they cool more.

174. A sweating horse loses a lot of heat by evaporation, which can lead to colds.

175. The leaves have many stomata on the underside. To reduce evaporation of moisture, the sheet is curled. Its lower side is less heated by the sun, and consequently, evaporates moisture less.

176. The hairs on the leaves of plants impede the movement of air near the surface of the leaves, thus they retain the formed vapors and help to slow down the evaporation of moisture from the surface of the leaves.

177. The thorns and thorns, replacing the leaves of many plants, help these plants use moisture more economically, since they are heated by the sun less than the leaves, and, therefore, evaporate much less water.

178. In the forest, the trees break the wind into separate streams and to a significant extent loses its strength. Therefore, even on a cloudy day, moisture evaporation there is less intense than in a meadow, and the grass in the forest dries more slowly.

179. During harrowing, soil capillaries are destroyed and moisture evaporation is significantly reduced.

180. Evaporation of sweat from the body of the animal promotes heat exchange, but the dog's sweat glands are located only on the pads of the "fingers", therefore, in order to increase the cooling of the body on a hot day, the dog opens its mouth wide and sticks out its tongue. The evaporation of saliva from the surface of her mouth and tongue lowers her body temperature.

186. The phenomenon of the transition of mechanical energy into the internal energy of the interaction of bodies (air - ship)

189. Plant saps are aqueous solutions of various salts that freeze at temperatures lower than 0 ° C.

190. With sharp temperature changes due to unequal coefficients of thermal expansion of dentin and enamel, large internal stresses arise in the tooth, which gradually destroy it.

191. The leaves of many plants contain oily substances, and therefore are not wetted with water.

192. They are unable to overcome surface tension forces.

193. Surface tension creates an elastic film on the water surface. Legs of water striders are not wetted with water and therefore do not penetrate into the depth. The surface film of water only slightly bends under the slight weight of the insect.

201. When birds crumple, the layer of air between feathers increases and, due to poor thermal conductivity, delays the transfer of heat from the bird's body to the surrounding space.

211. All the mechanical energy of the bird when braking in the snow is converted into internal energy.

212. Exhaust gases do work due to a decrease in their internal energy and, consequently, a decrease in temperature.

213. The density of birch is greater than that of pine. Therefore, the mass of birch wood with a volume of 1 cubic meter is greater than the mass of pine wood of the same volume.

217. The juices contained in the tree, when frozen, increase in volume and at the same time tear apart the fibers of the plant with a crash.

224. ≈0.48 m / s.

230. efficiency = (1- ) ∙ 100% = 80%; 10 5 W

231. Efficiency = 1-T 2 mR \ (ρVμ) = 0.5

234. ≈2.26 kg. During operation, when the vehicle skids, the internal energy of the snow increases. Due to this energy, the snow heats up to the melting point and melts, therefore we get: A = Q 1 + Q 2. since A = Pt, and Q 1 = cm (t-t 0) and Q = mλ, the equation can be written as:

Pt = сm (t-t 0) + mλ or Pt = m (с (t-t 0) + λ)

Where: m =
... Substituting the numerical values, we get: ≈2.26 kg

235. Yes, but as a result of the rapid melting of the ice, the flood would be super-abundant.

247. At high altitude, the air is oversaturated with water vapor. The aircraft introduces condensation centers on which steam condenses.

251. will not decrease.

256. Low humidity promotes moisture evaporation and cooling of the skin and respiratory organs.

285.3.36W; 6,

288.198 bulbs

285.3.36W; 6.72W ∙ h

Electricity and magnetism.

272. The most famous electric fish are electric eel, electric ray and electric catfish. These fish have special organs for storing electrical energy. Small stresses arising in ordinary muscle fibers are summed up here due to the sequential inclusion of many individual elements, which are connected by nerves, like conductors, into long batteries. So the electric eel, which lives in the waters of tropical America, has up to 8 thousand plates, separated from one another by a gelatinous substance. A nerve extending from the spinal cord goes to each plate. From the point of view of physics, these devices represent a kind of large-capacity capacitor system. The eel, accumulating energy in its capacitors and discharging it at its discretion through the body that touches it, produces electrical shocks that are extremely sensitive to humans and fatal to small animals. In a large eel that does not discharge for a long time, the voltage at the moment of impact can reach 800 V. Usually, it is somewhat less.

Among other electric fish, the torpedo stingray, which is found in the Atlantic, Indian and Pacific oceans, stands out. The dimensions of the torpedo reach two meters, and its electrical organs consist of several hundred plates. The torpedo is capable of giving 150 discharges per second for 10-16 seconds, 80V each. Electrical organs of large dashboards develop a voltage of up to 220V.

A special type of electric organ in an electric catfish, giving discharges up to 360V. His electrical organ is located in a thin layer under the skin all over the body.

A characteristic feature of fish with electrical organs is their low susceptibility to the action of electric current. Some can handle up to 220V.

273. Electric current passed along the wet film of the body surface and did not penetrate into the body, so the rat remained unharmed.

274. The current, passing through the human body, affects the central and peripheral nervous systems, causing disturbances in the work of the heart and respiration.

275. Of all the tissues that make up the body, the outer layers of the skin have the least conductivity, the nerve fibers are the most conductive, therefore the current in the body passes mostly along the nerve fibers and thereby affects the entire nervous system.

276. Ideal insulators do not exist, even porcelain, from which high-voltage insulators are made, changes its properties depending on the weather. The slightly dusty and damp surface of the insulator serves as a current conductor. If we take into account that a high voltage current flows through the wires, then its leakage, even a small one, will be life-threatening.

277. Trees with roots that penetrate deep water-bearing layers of the soil are better connected to the ground and therefore, under the influence of electrified clouds, significant charges of electricity flowing from the ground accumulate on them, having a sign opposite to the sign of the cloud charge.

278. In no case should you think that if you stand under a lightning rod during a thunderstorm, it will always protect you from lightning. If you stand even at a short distance from the lightning rod, then an induced charge is formed in your body at the moment of the lightning strike. A discharge in the form of a spark can easily occur between it and the charge of the lightning rod. All of these considerations apply to tall, lonely standing trees. If you are standing in the steppe at a distance of tens of meters from a lonely standing tree, then you are better protected from a lightning snowball than if there were no tree. If a person is near a tree, it may happen that lightning in some cases chooses its path through the human body, since it is the same conductor as a tree.

279. Birds most often perish in three cases when, sitting on a wire, they touch the post with their wing, tail or beak, that is, they connect to the ground.

280. The described phenomenon is called "the fires of St. Elmo". This is a very rare occurrence. On the points, on the posts of the fences, sometimes even on the heads of people, a bluish light appears. It is a quiet discharge - the movement of electrons in air at atmospheric pressure and high voltage.

297. The body of a bird can be viewed as a parallel connection to the section of the high-voltage circuit, enclosed between the legs of the bird. Since the resistance of the bird is much higher than the resistance of this area, the current strength in the body of the bird is very small and harmless to it.

321. It has been established that a magnetic field is formed along the excited nerve approximately 0.0005 s before the transmission of the excitation. Apparently, at the moment of irritation, the molecules carrying a charge somehow change their position in space, allowing a wave of excitation to pass along the nerve. It is this movement of molecules that is probably the reason for the appearance of the magnetic field.

322. In the rivers of Africa, fish were found, equipped with a real radar. This is a water elephant. It turned out that the electric generator located in its tail part constantly emits low-frequency oscillations (up to 100 pulses per minute), which are captured by the special organs of this fish located at the base of the fin. Therefore, it is not surprising that the water elephant, even burrowing headlong into the silt, senses the approach of a predator at a distance and manages to hide in time. The electric eel has the same locator.

323. Chemical

Optics.

342. The eye perceives light with the help of light-sensitive cells: cones and rods. More sensitive - rods and less sensitive - cones. In low light, light is perceived by rods rather than cones. But sticks do not provide color sensations, so all objects appear gray.

343. In the air, the outer cornea of ​​the eye collects light rays, creates an image on the retina, and the lens only helps a little in this. However, under water, the action of the cornea is reduced to zero due to the fact that the refractive indices of water and the liquid inside our eye are almost the same and the rays, without refraction, pass directly through the cornea. Under water we become, as it were, farsighted.

344. The refractive index of the insect's body is close to the refractive index of water, and the refractive index of the eye is different from the refractive index of water. Light would pass through transparent eyes without irritating the optic nerves. These organisms are visible in the air.

345. Such an original structure of the eyes is explained by the fact that both underwater organisms and aerial insects serve as food for the four-eyed. Swimming near the surface of the water, the fish puts out the upper halves of the eyes and monitors what is being done above the water. The lower halves of the eyes monitor what is happening in the water.

346. The horizontal position of the pupil expands the angle of view in the horizontal plane. This is very important for animals that live on flat, open plains, where predators need to be spotted well in advance as soon as they appear on the horizon. In cats and foxes, the pupils are located vertically because these animals, looking for their prey, most often look up and down.

347. The retina of the eye is covered from the inside with a film consisting of many small cells - cones and rods. The cones allow you to see during the day, and the rods allow you to see at night. The peculiarities of vision of chickens and owls are due to the fact that the retina of the eye in chickens consists only of cones, and in owls - only of rods.

348. The eyes of man and some animals are adapted to the simultaneous examination of some object: the field of view of the right eye only slightly does not coincide with the field of view of the left eye. Most animals look with each eye separately. The objects they see do not differ in relief, but their field of view is much wider.

349. The eye of a falcon is designed in such a way that the lens can become almost flat, as a result of which the image of distant objects falls on the retina.

350. Animals of white color radiate less heat into the surrounding space, which is especially important in the north.

351. Dark color absorbs heat rays well. This allows insects to have a body temperature significantly higher than the ambient air temperature in sunny weather.

352. In the twilight under the dense branches of fir trees, only a white or pale pink color is clearly visible from afar, therefore insects, in search of nectar, pollinate only these flowers.

353. Many fish have a dark back and a silvery belly. From above, the dark back of the fish is not visible against the background of the dark bottom. From the water, the surface of the river looks like a mirror, and since the belly of the fish is silvery, it is difficult for aquatic predators to notice it from below.

346. The iridescent tints of the wings of some insects are caused by interference phenomena. A similar phenomenon is observed on the feathers of many birds.

Nuclear physics.

354. Even in chemically pure uranium the share of uranium is 235 less than 1%. Therefore, the emitted neutrons are mainly absorbed by the nuclei of uranium-238 without further nuclear fission.

356. m = m 1

357. m = m 0 = 26.9 kg

358.Safe, since the absorbed dose per year is 8.4 mGy.

359. Natural uranium contains only ≈0.7% of uranium-235 and the probability of a slow neutron meeting with the nucleus of uranium-235 is small. The fission of uranium-238 nuclei is carried out by very fast neutrons, the number of which is very small.

Since ancient times, the parable of a pampered Roman accustomed to a warm climate has come down to us, who came to visit a half-naked and barefoot Scythian. "Why aren't you freezing?" - asked the Roman, wrapped from head to toe in a warm toga and nevertheless shivering from the cold. "Is your face freezing?" the Scythian asked in turn. Having received a negative answer from the Roman, he said: "I am all like your face."

Already from the above example, it can be seen that resistance to cold largely depends on whether a person is regularly engaged in cold hardening. This is confirmed by the results of observations of forensic experts who studied the causes and consequences of shipwrecks that occurred in the icy waters of the seas and oceans. Unhardened passengers, even with life-saving equipment, died from hypothermia in ice water in the first half hour. At the same time, cases were recorded when individual people fought for life with the piercing cold of icy waters for several hours.

So, during the Great Patriotic War, Soviet sergeant Pyotr Golubev swam 20 km in icy water in 9 hours and successfully completed a combat mission.

In 1985, an English fisherman demonstrated an amazing ability to survive in icy water. All his comrades died from hypothermia 10 minutes after the shipwreck. He swam in the icy water for more than 5 hours, and when he reached the ground, he walked barefoot along the frozen, lifeless shore for about 3 hours.

A person can swim in icy water even in very severe frost. At one of the winter swimming holidays in Moscow, Hero Soviet Union Lieutenant General G. E. Alpaidze said: “I have been experiencing the healing power of cold water for 18 years already. That is how much I constantly swim in winter. During his service in the North, he did this even at an air temperature of -43 ° C. I am sure that swimming in frosty weather is the highest stage of hardening the body. One cannot but agree with Suvorov, who said that "ice water is good for the body and mind."

In 1986, "Nedelya" reported on the 95-year-old "walrus" from Yevpatoria, Boris Iosifovich Soskin. At the age of 70, he was pushed into the hole by sciatica. After all, correctly selected doses of cold are able to mobilize the reserve capabilities of a person. And it is no coincidence that in Japan and the Federal Republic of Germany, for the treatment of some forms of rheumatism, the "antisauna" invented by the Japanese professor T. Yamauchi is used. The procedure takes a little time: a few minutes in the "dressing room" at -26 ° C, and then exactly 3 minutes in the "bath" at -120 °. The patients have masks on their faces, thick gloves on their hands, but the skin in the area of ​​sore joints is completely naked. After one cold session, joint pain disappears for 3-4 hours, and after a three-month course of cold treatment for rheumatoid arthritis, it seems that there is no trace left.

More recently, it was believed that if a drowned person was not pulled out of the water within 5-6 minutes, he would inevitably die as a result of irreversible pathological changes in the neurons of the cerebral cortex associated with acute oxygen deficiency. However, in cold water this time can be much longer. For example, in the state of Michigan, a case was recorded when an 18-year-old student, Brian Cunningham, fell under the ice of a frozen lake and was removed from there only 38 minutes later. He was brought back to life with the help of artificial respiration with pure oxygen. Earlier, a similar case was reported in Norway. Five-year-old boy Vegard Slettemuen from the city of Lillestrom fell through the ice of the river. After 40 minutes, the lifeless body was dragged ashore, artificial respiration and heart massage began. Signs of life soon appeared. Two days later, the boy regained consciousness, and he asked: "Where are my glasses?"

Such accidents with children are not that uncommon. In 1984, four-year-old Jimmy Tontlevitz fell under the ice of Lake Michigan. After 20 minutes in ice water, his body cooled to 27 °. Nevertheless, after 1.5 hours of intensive care, the boy was returned to life. Three years later, seven-year-old Vita Bludnitsky from the Grodno region had to stay under the ice for half an hour. After thirty minutes of cardiac massage and artificial respiration, the first breath was recorded. Another case. In January 1987, a two-year-old boy and a four-month-old girl, having fallen in a car into a Norwegian fjord to a depth of 10 m, were also brought back to life after a quarter of an hour under water.

In April 1975, 60-year-old American biologist Warren Churchill conducted a fish census on a lake covered with floating ice. His boat capsized, and he was forced to stay in cold water at a temperature of + 5 ° C for 1.5 hours. By the time the doctors arrived, Churchill was no longer breathing, all turned blue. His heart was barely audible, and the temperature of his internal organs dropped to 16 ° C. Nevertheless, this person survived.

An important discovery was made in our country by Professor A. S. Konikova. In experiments on rabbits, she established that if, no later than 10 minutes after death, the body of an animal is quickly cooled, then after an hour it can be successfully revived. Probably, this can explain the amazing cases of people reviving after a long stay in cold water.

In the literature, there are often sensational reports about human survival after a long stay under a block of ice or snow. It is difficult to believe in this, but a person is still able to endure short-term hypothermia.

A vivid example of this is the case of the famous Soviet traveler G.L. Travin, who in 1928-1931. solo on a bicycle traveled along the borders of the Soviet Union (including the ice of the Arctic Ocean). In the early spring of 1930, he settled for the night as usual, right on the ice, using ordinary snow instead of a sleeping bag. At night, a crack formed in the ice next to his overnight stay, and the snow that covered the brave traveler turned into an ice shell. Leaving a part of his clothes frozen in the ice, GL Travin with frozen hair and an "ice hump" on his back reached the nearest Nenets plague. A few days later, he continued his cycling journey across the ice of the Arctic Ocean.

It has been repeatedly noticed that a freezing person can fall into oblivion, during which it seems to him that he is in a very heated room, in a hot desert, etc. In a semi-conscious state, he can throw off his boots, outerwear and even underwear. There was a case when a criminal case of robbery and murder was initiated against a frozen man who was found naked. But the investigator found that the victim undressed himself.

But what an extraordinary story happened in Japan with the driver of a refrigerated car Masaru Saito. On a hot day, he decided to relax in the back of his refrigerator. In the same body there were blocks of "dry ice", which were frozen carbon dioxide. The door of the van slammed shut, and the driver was left alone with the cold (-10 ° С) and the CO 2 concentration rapidly increasing as a result of the evaporation of "dry ice". It was not possible to establish the exact time during which the driver was in these conditions. In the case of a wreath, when he was pulled out of the body, he was already frozen, nevertheless, a few hours later the victim was revived in the nearest hospital.

It must be said that very high concentrations of carbon dioxide are required to obtain such an effect. We had to observe two volunteers who were at zero air temperature in the same swimming trunks for about an hour and all this time breathed a gas mixture containing 8% oxygen and 16% carbon dioxide. One of them did not feel cold at the same time, did not tremble and cooled down on average every 5 minutes by 0.1 °. However, the other person continued to shiver from the cold all this time, thereby increasing the formation of heat in the body. As a result, his body temperature remained almost unchanged.

At the time of the onset of a person's clinical death from hypothermia, the temperature of his internal organs usually decreases to 26 - 24 ° C. But there are also known exceptions to this rule.

In February 1951, a 23-year-old black woman was brought to a hospital in the American city of Chicago, who lay in very light clothes for 11 hours in the snow with air temperature fluctuations from -18 to -26 ° C. The temperature of her internal organs at the time of admission to the hospital was 18 ° C. Even surgeons rarely decide to cool a person to such a low temperature during complex operations, because it is considered the limit below which irreversible changes can occur in the cerebral cortex.

First of all, the doctors were surprised by the fact that with such a pronounced cooling of the body, the woman was still breathing, although rarely (3-5 breaths per minute). Her pulse was also very rare (12-20 beats per minute), irregular (pauses between heartbeats reached 8 s). The victim managed to save her life. True, her frostbitten feet and fingers were amputated.

A little later, a similar case was registered in our country. On a frosty March morning in 1960, a frozen man, found by workers of a construction site on the outskirts of the village, was delivered to one of the hospitals in the Aktobe region. At the first medical examination of the victim, the protocol was written: “A numb body in icy clothes, without a headdress and shoes. The limbs are bent at the joints and it is not possible to straighten them. When tapping on the body, a dull sound, as from striking a tree. The body surface temperature is below 0 ° C. The eyes are wide open, the eyelids are covered with an icy edge, the pupils are dilated, cloudy, and there is an ice crust on the sclera and iris. The signs of life - heartbeat and breathing - are not detected. Diagnosed with general freezing, clinical death. "

It is difficult to say what motivated the doctor P. S. Abrahamyan, whether professional intuition, or professional unwillingness to come to terms with death, but he still put the victim in a hot bath. When the body was freed from the ice cover, they began a special complex of resuscitation measures. After 1.5 hours, weak breathing and a barely perceptible pulse appeared. By the evening of the same day, the patient regained consciousness.

Questioning helped to establish that V.I.Kharin, born in 1931, lay in the snow without boots and headgear for 3-4 hours. The consequence of his freezing was bilateral croupous pneumonia and pleurisy, as well as frostbite of the fingers, which had to be amputated. In addition, for four years after freezing, V.I.Kharin retained functional disorders of the nervous system. Nevertheless, the "frozen" remained alive.

If Kharin had been brought in our time to the specialized city clinical hospital No. 81 in Moscow, it would probably have done even without amputation of the fingers. Frozen people are saved there not by immersion in a hot bath, but by injecting drugs into the central vessels of the icy areas of the body that thin the blood and prevent its cells from sticking together. Warm streams slowly but surely break through the vessels in all directions. Cell by cell awaken from deadly sleep and immediately receive a life-saving "sip" of oxygen and nutrients.

Here's another interesting example. In 1987, in Mongolia, M. Munkhzai's child lay for 12 hours in a field in 34-degree frost. His body was stiff. However, after half an hour of resuscitation, a barely discernible pulse appeared (2 beats in 1 min). A day later, he moved his hands, after two - he woke up, and a week later he was discharged with the conclusion: "There are no pathological changes."

At the heart of such an amazing phenomenon lies the body's ability to respond to cooling without activating the mechanism of muscle tremors. The fact is that the activation of this mechanism, designed at any cost to maintain a constant body temperature under cooling conditions, leads to the "combustion" of the main energy materials - fats and carbohydrates. Obviously, it is more profitable for the body not to fight for a few degrees, but to slow down and synchronize the processes of life, to make a temporary retreat to the 30-degree mark - this way, forces are preserved in the subsequent struggle for life.

There are cases when people with a body temperature of 32-28 ° C were able to walk and talk. Recorded preservation of consciousness in chilled people at a body temperature of 30-26 ° C and meaningful speech even at 24 ° C.

Is it possible to increase the body's resistance to cooling? Yes, you can use hardening. Hardening is necessary primarily to increase the resistance of the human body to factors that cause colds. Indeed, 40% of patients with temporary disability lose it precisely because of the common cold. Colds, according to the calculations of the State Planning Committee of the USSR, cost the country more expensive than all other diseases combined (up to 6 billion rubles a year!). And the fight against them must be started from early childhood.

Many parents believe that colds in children are inevitable in urban settings. But is it? More than twenty years of experience of a large family of teachers Nikitin showed that children can live without getting sick, provided they are properly trained. Many families picked up the Nikitinskaya baton. Let's take a look at one of them - the Moscow family of Vladimir Nikolaevich and Elena Vasilievna Kozitsky. Elena Vasilievna - teacher, mother of 8 children. In the "pre-Nikitin era" all of them often suffered from colds, and one child even had bronchial asthma. But in one, and then in another room of a three-room apartment, children's sports complexes appeared. Shorts have become the usual clothes for children at home. Regular hardening was complemented by pouring cold water and walking barefoot, even in the snow. Each child was given the opportunity to sleep on the balcony at any time of the year. Nutrition has also changed.

From the products, the children were given everything they wanted, and gradually all of them, except for the oldest child, who was already 11 years old, lost their taste for meat food. Fresh vegetable and dairy products have become the basis of children's nutrition.

As a result of this complex of health-improving measures, the incidence of children has dropped sharply. Now only occasionally did one of them catch a slight cold, while losing their appetite. The parents knew that loss of appetite in case of a cold is a natural defense reaction of the body, and in such cases they did not force-feed the children. Appetite returned to them, as a rule, after one or two days, along with normal health.

The example of the Kozitsky family turned out to be contagious. Neighbors and acquaintances began to bring their children to them "for re-education." A kind of home health kindergarten was formed. And this case is not isolated. In Moscow, there is a special parent club for the so-called non-standard parenting. More recently, a similar club was created in Leningrad. Members of these clubs are parents who strive to master the art of being healthy and teach this art to their children.

Interestingly, in the GDR there were children's winter swimming sections for boys and girls 10-12 years old. Preliminary preparation for winter swimming in these sections is carried out within 7 weeks:

1st week - rubdown with cool water, gymnastics at open windows or outdoors;

2nd week - cold shower;

3rd week - rubdown with snow;

4-6 weeks - entering the ice water up to the thighs;

7th week - full immersion in ice water.

In our country, in the Moscow club "Healthy Family" and the Leningrad club "Nevskie morzhata" children are bathed in ice water even at infancy: they usually do no more than three immersions of the baby with his head under the water for up to 4 seconds. Such "walruses" do not get sick with anything. One of us (A. Yu. Katkov) was convinced of this by the example of his own sons.

A person can withstand single combat with a 50-degree frost, almost without resorting to warm clothes. Exactly this possibility was demonstrated in 1983 by a group of climbers after climbing the summit of Elbrus. Wearing only swimming trunks, socks, mittens and masks, they spent half an hour in a thermobaric chamber - in a severe cold and rarefied atmosphere, corresponding to the height of the peak of Communism. The first 1-2 minutes, the 50-degree frost was quite tolerable. Then a strong shiver began to beat from the cold. There was a feeling that the body was covered with an ice shell. In half an hour, it cooled down by almost a degree.

"Our strengthening frost is useful for Russian health ..." - A. Pushkin once wrote. Today, the healing power of frost is recognized far beyond the borders of our country.

So, in 100 cities of the Soviet Union not so long ago there were about 50 thousand winter swimming lovers, or "walruses". Approximately the same number of "walruses" ended up in the German Democratic Republic.

Physiologist Yu. N. Chusov studied the reaction to cold of Leningrad "walruses" during their winter swimming in the Neva. The studies carried out led to the conclusion that winter bathing causes an increase in oxygen consumption by the body by 6 times. This increase is due to both involuntary muscle activity (cold muscle tone and tremors) and voluntary (warm-up before bathing, swimming). After bathing in winter, in almost all cases, there is a visible tremor. The time of its occurrence and intensity depend on the duration of the "winter swimming". Body temperature while staying in ice water begins to decrease after about 1 minute of bathing. In long-term swimming "walruses" it decreases to 34 ° С. The recovery of temperature to its original normal level usually occurs within 30 minutes after the end of the single combat with ice water.

A study of the heart rate in "walruses" showed that after 30 seconds in ice water without active muscle movements, it decreases on average from 71 to 60 beats per minute.

Under the influence of cold hardening in "walruses" the heat production of the body increases. And it not only increases, but also becomes more economical due to the predominance of free oxidation processes in the body. During free oxidation, the released energy does not accumulate in the form of reserves of adenosine triphosphoric acid (ATP), but is immediately converted into heat. A hardened organism even allows itself such a luxury as the expansion of peripheral vessels adjacent directly to the skin. This, of course, leads to an increase in heat loss, but additional heat loss is successfully compensated by an increase in heat generation in the body due to free oxidation. But due to the rush to the surface tissues of the body through the arterial vessels of oxygen-rich "hot" blood, the likelihood of frostbite decreases.

Interestingly, when the fingers are cooled, due to the narrowing of the capillaries, the thermal insulating properties of the skin can be increased by 6 times. But the capillaries of the scalp (with the exception of the facial part) do not have the ability to narrow under the influence of cold. Therefore, at a temperature of -4 ° C, about half of all the heat produced by the body at rest is lost through the cooled head if it is not covered. But immersion of the head in ice water for more than 10 seconds in untrained people can cause a spasm of the vessels supplying the brain.

All the more surprising is the incident that took place in the winter of 1980 in the village of Novaya Tura (Tatar Autonomous Soviet Socialist Republic). In the 29-degree frost, 11-year-old Vladimir Pavlov did not hesitate to dive into the wormwood of the lake. He did this in order to save a four-year-old boy who had gone under the ice. And he saved him, although for this he had to dive three times under the ice to a depth of 2 m.

Swimming in ice water can be used for medicinal purposes if the dosage is correct. For example, in the 1st city hospital of Kaluga, neuropathologist Ya. A. Petkov recommends winter bathing in the Oka to eliminate headaches and heartaches of neurotic origin, as well as attacks of bronchial asthma. Probably, this method of treatment is based, as IP Pavlov said, "shaking up the nerve cells," that is, the positive effect of excessively cold water on the central nervous system.

On the southern coast of Crimea in the Yalta sanatorium named after SM Kirov, for a number of years, sea bathing in winter has been used to treat patients with functional disorders of the central nervous system. Before plunging into the cold sea waves (the water temperature is usually not lower than 6 ° C), patients undergo a special hardening complex during the first week: air baths in the ward, night sleep on the verandas, daily washing their feet at night with cold water, walking, morning exercises in the open air, close tourism. Then they gradually begin to take sea baths lasting up to 3-4 minutes. Thus, neurasthenia and stage I hypertension are well cured.

The hardening of the body has no absolute contraindications. When used correctly, it can help the body "scramble" out of very serious ailments. An illustrative example is the personal experience of Yuri Vlasov. This is how he writes about it in his book "Concourse of Difficult Circumstances": "The first walks ... eight - twelve minutes of stomping near the entrance. There was no strength for more. I got wet and started to feel sick. During these first weeks my wife and daughter accompanied me. They carried spare things with them - all of a sudden I would feel chilled or the wind would sweep over me. Yes, yes, I was pathetic and ridiculous. I was like that, but not my determination.

I stubbornly stomped along the winter paths and chanted spells against colds. Gradually, I got into a fairly quick step without shortness of breath and sweat. This gave me confidence, and already in February I gave up the coat. Since that time, I only wear jackets and every year in more and more light ones.

I am done away with, so to speak, with the power of the plaid and the woolen shirt. Let the night fevers plague - I will get up and change the sheets, but just not pamper myself with a blanket! Due to the microclimate under the woolen shirt, I was susceptible to any cooling. If before there was a need for such underwear, now I will get rid of it. There is nothing more pampering and therefore dangerous from clothes. I have forever given up on sweaters with blind collars for a good part of my neck and scarves. Here in the city and our climate there are no conditions that would justify such clothes. Feeliness makes us susceptible to colds. I have generally revised and thoroughly lightened the wardrobe. Turning unnecessarily to unnecessarily warm things, we derail our defenses, make ourselves vulnerable to colds, and, consequently, more serious illnesses. "

The later years of Yuri Vlasov's life are also convincing of the correctness of these words: today he is practically healthy and creatively active.

It has now been established that, when used correctly under medical supervision, winter swimming can be a good helper in normalizing the following health abnormalities:

cardiovascular diseases without circulatory disorders - stage I hypertension, atherosclerotic cardiosclerosis and myocardial dystrophy without compensation violations, arterial hypotension without severe weakness, neurocirculatory dystonia;

lung diseases - inactive forms of tuberculosis in the phase of compaction and stable compensation, focal pneumosclerosis in the phase of remission;

diseases of the central nervous system - moderate forms of neurasthenia;

diseases of the peripheral nervous system - radiculitis, plexitis (without violation of compensation), with the exception of the period of exacerbation;

diseases of the gastrointestinal tract: chronic gastritis, enteritis and colitis with a satisfactory general condition and the absence of pronounced spastic phenomena;

some metabolic disorders.

In recent years, speed swimming competitions in ice water have become more and more popular. In our country, such competitions are held in two age groups at a distance of 25 and 50 m.For example, the winner of one of the recent competitions of this type was the 37-year-old Muscovite Evgeny Oreshkin

swam in icy water a 25-meter distance in 12.2 seconds. In Czechoslovakia, winter swimming competitions are held at distances of 100, 250 and 500 m. The super-hardened ones make a swim even 1000 m, staying in ice water continuously for up to 30 minutes.

In addition to "winter swimming" there is such a harsh method of hardening as running in shorts in frosty weather. The familiar to us Kiev engineer Mikhail Ivanovich Oliyevsky, in this uniform, ran a distance of 20 km in 20-degree frost. In 1987, one of us (A. Yu. Katkov) joined Olievsky in such a race in a frost of 26 ° pa for half an hour. Fortunately, there was no frostbite thanks to regular hardening by other methods (swimming in an ice hole, light clothing in winter).

"Walruses", of course, are a seasoned people. But their resistance to cold is far from the limit of human capabilities. The natives of central Australia and Tierra del Fuego (South America), as well as the Bushmen of the Kalahari Desert (South Africa), are even more immune to cold.

The high resistance to cold of the indigenous inhabitants of Tierra del Fuego was observed by Charles Darwin during his journey on the Beagle. He was surprised that completely naked women and children did not pay any attention to the thickly falling snow that was melting on their bodies.

In 1958-1959 American physiologists studied the cold resistance of the aborigines of central Australia. It turned out that they are sleeping naked on the bare ground between fires quite calmly at an air temperature of 5-0 ° C, sleeping without the slightest signs of trembling and increased gas exchange. At the same time, the body temperature of the Australians remains normal, but the temperature of the skin drops on the body to 15 °, and on the limbs - even to 10 ° C. With such a pronounced decrease in skin temperature, ordinary people would experience sensations of almost unbearable pain, while Australians sleep peacefully and do not feel pain or cold.

How can one explain that acclimatization to the cold among the listed peoples proceeds in such a peculiar way?

It seems that the whole point here is forced malnutrition and intermittent starvation. The body of a European responds to cooling by increasing heat production by increasing the level of metabolism and, accordingly, increasing the consumption of oxygen by the body. This way of adaptation to cold is possible only, firstly, with short-term cooling, and secondly, with normal nutrition.

The peoples of which we are talking are forced to be in cold conditions without clothes for a long time and inevitably experience an almost constant lack of food. In such a situation, there is practically only one way to adapt to the cold - limiting heat transfer from the body due to narrowing of peripheral vessels and, accordingly, reducing the temperature of the skin. At the same time, the Australians and many other natives in the process of evolution developed an increased resistance of body surface tissues to oxygen starvation, which arises from the narrowing of the blood vessels feeding them.

This hypothesis is supported by the fact that resistance to cold increases after multi-day metered fasting. This feature is noted by many "starvationists". And it can be explained simply: during starvation, both heat production and heat transfer from the body decrease. After starvation, heat production as a result of an increase in the intensity of oxidative processes in the body increases, but heat transfer can remain the same: after all, the tissues of the body surface, as less important for the body, get used to the lack of oxygen during prolonged fasting and, as a result, become more resistant to cold.

In our country, an interesting system of cold hardening was promoted by P.K. Ivanov. He has been hardening for more than 50 years (starting after 30) and has achieved amazing results. In any frost, he walked barefoot in the snow in only shorts, and not for minutes, but hours, and did not feel any cold at the same time. P.K. Ivanov combined cold hardening with dosed fasting and self-hypnosis of insensitivity to cold. He lived for about 90 years, and even the last years were not overshadowed by ill health.

We know that the young geologist V.G. Trifonov resorts to the same methods of increasing the body's resistance to cold. In Kamchatka, he was shocked by the news of the death from freezing of two of his comrades - practically healthy men. They could not stand the fight with the cold, although the deer accompanying them survived and safely reached their dwelling. VG Trifonov performed a number of Cold experiments on himself. The results allowed him to draw the same conclusion that the courageous "Robinsons" of the Atlantic - the Frenchman A. Bombard and the German H. Lindemann - came to before him: most often a person dies not from the cold, but from fear of him.

In the literature, there is a report about the American Bullison, who lived at the beginning of this century, who for 30 years ate exclusively raw plant foods, periodically starved for 7 weeks and wore the same "bathing cloak" all year round in any weather.

On March 26, 1985, the newspaper Trud reported about 62-year-old A. Maslennikov, who spent 1.5 hours in the snow barefoot, without clothes and without a hat. Thanks to 35 years of hardening experience, including "winter swimming", this person did not even get a cold.

Another example of the heroic single combat of a person with the cold. In February 1977, Komsomolskaya Pravda wrote about the extraordinary willpower of the young Air Force pilot Yuri Kozlovsky. In flight, during the test of the aircraft, an emergency occurred. He catapulted over the Siberian taiga from a dying plane. When landing on sharp stones, he received open fractures of both legs. The frost was 25-30 ° C, but the ground was bare, without a snowflake. Overcoming terrible pain, cold, thirst, hunger and fatigue, the pilot crawled for three and a half days until he was picked up by a helicopter. At the time of delivery to the hospital, the temperature of his internal organs was 33.2 ° C, he lost 2.5 liters of blood. The legs were frostbitten.

And yet, Yuri Kozlovsky survived. He survived because he had a goal and a duty: to tell about the plane that he experienced, so that the accident would not happen again with those who should fly after him.

The case with Yuri Kozlovsky involuntarily brings us back to the years of the Great Patriotic War, when Alexey Maresyev found himself in a similar situation, who later became a Hero of the Soviet Union. Yuri also had both legs amputated, and he was operated on twice due to severe gangrene. In the hospital, he developed a perforated duodenal ulcer, renal failure, and his hands were inactive. Doctors saved his life. And he disposed of it with dignity: he lives full-bloodedly and actively. In particular, having shown extraordinary willpower, he learned to walk on prostheses the way he walked on his own legs before his misfortune.

Doctor L.I. Krasov lives in Moscow. This man received a serious injury - a fracture of the spine with damage to the spinal cord in the lumbar region. As a result, atrophy of the gluteal muscles, paralysis of both legs. Friends-surgeons patted him as best they could, but they did not hope that he would survive. And he "spite all deaths" restored the damaged spinal cord. The main role, he believes, was played by the combination of cold hardening with dosed fasting. Of course, all this would hardly have helped if this person did not have extraordinary willpower.

What is willpower? In fact, this is not always conscious, but a very strong self-hypnosis.

Self-hypnosis also plays an important role in the cold hardening of one of the peoples living in the mountainous regions of Nepal and Tibet. In 1963, a case of extreme cold resistance of a 35-year-old mountaineer named Man Bahadur was described, who spent 4 days on a high-mountain glacier (5-5.3 thousand m) at an air temperature of minus 13-15 ° C barefoot, in poor clothes, no food. Almost no significant violations were found on him. Studies have shown that with the help of self-hypnosis, he could increase his energy exchange in the cold by 33-50% through "non-contractive" thermogenesis, i.e. without any manifestations of "cold tone" and muscle tremors. This ability saved him from hypothermia and frostbite.

But perhaps the most surprising is the observation of the famous explorer of Tibet, Alexandra Da-vid-Nel. In her book "Magicians and Mystics of Tibet" she described the contest, which is held at the holes cut in the ice of a high-mountain lake, naked to the waist, yoga-spas. Frost under 30 °, but steam comes down from the respawns. And no wonder - they compete, how many sheets, pulled out of the icy water, each will dry on his own back. To do this, they cause in their body a state when almost all the energy of vital activity is spent on generating heat. The respawns have certain criteria for assessing the degree of thermal energy management of their body. The student sits in the lotus position in the snow, slows down breathing (as a result of the accumulation of carbon dioxide in the blood, the superficial blood vessels expand and the body's heat release increases) and imagines that the flame is growing stronger along his spine. At this time, the amount of snow melted under the seated person and the radius of melting around him are determined.

How can you explain such a physiological phenomenon that seems downright incredible? The answer to this question is given by the research results of the Alma-Ata scientist A.S. Romen. In his experiments, volunteers arbitrarily increased their body temperature by 1-1.5 ° C in just 1.5 minutes. And they achieved this again with the help of active self-hypnosis, imagining themselves somewhere in a steam room on the uppermost shelf. Roughly the same technique is used by yoga-respas, bringing the ability of an arbitrary increase in body temperature to amazing perfection.

Cold can promote longevity. It is no coincidence that the third place in the percentage of centenarians in the USSR (after Dagestan and Abkhazia) is occupied by the center of longevity in Siberia - the Oymyakon region of Yakutia, where frosts sometimes reach 60-70 ° С. Residents of another center of longevity, the Hunza Valley in Pakistan, bathe in icy water even in winter when it is 15 degrees below zero. They are very frost-resistant and only heat their stoves to cook food. The rejuvenating effect of cold against the background of rational nutrition is reflected there primarily in women. At 40, they are considered quite young, almost like our girls, at 50-60 they retain their slimness and gracefulness, at 65 they can give birth to children.

Some nationalities have a tradition of accustoming the body to the cold from infancy. “The Yakuts,” wrote the Russian academician IR Tarkhanov at the end of the last century in his book “On the hardening of the human body,” “rub their newborns with snow, and the Ostyaks, like the Tungus, immerse the babies in snow, pour ice water over them and then wrap them in deer skins ".

Of course, a modern city dweller should not resort to such risky methods of hardening children. But many people like such a simple and effective way of hardening, like walking barefoot.

To begin with, this technique was the only way for our ancestors to walk on the earth. Even in the last century, children from Russian villages had only one pair of boots per family, so they had to temper their legs from early spring to late autumn.

Walking barefoot as a local hardening technique was one of the first to suggest at the end of the 19th century. German scientist Sevastian Kneip. He put forward hygienic slogans that were bold for that time: "The best footwear is no footwear," "Every barefoot step is an extra minute of life," etc. Kneipp's views are shared by many doctors in our time. For example, in some sanatoriums of the German Democratic Republic, Germany, Austria, Finland, barefoot walking on the so-called contrasting paths is widely used, different parts of which are heated in different ways - from cold to hot.

I must say that the foot is a special part of our body; there is a rich field of nerve endings-receptors here. According to the ancient Greek legend, it was through the feet of Antey that he received an influx of new forces from mother earth to fight Hercules. And there is probably some truth in this. After all, the rubber sole isolates us from the negatively charged earth, and the positively charged atmosphere steals some of the negative ions from a person. When walking barefoot, we may receive, like Antaeus, the negative ions we lack, and with them electrical energy. However, this assumption needs experimental verification.

Academician I. R. Tarkhanov believed that “by artificially pampering the legs, we brought the matter to the point that the parts, naturally least sensitive to temperature fluctuations, were the most sensitive to colds. This trait is so widely recognized that polar explorers, when recruiting people, are guided, among other things, by the endurance of their soles to the cold, and for this purpose they are forced to stand with their bare soles on the ice to see how long they can endure it. "

In the United States, a similar technique was used when selecting astronauts for the Mercury program. To test willpower and endurance, the astronaut candidate was asked to keep both feet in ice water for 7 minutes.

An interesting annual plan of measures for local hardening of legs was recently developed by the Voronezh specialists V.V. Krylov, Z. E. Krylova and V. E. Aparin. It begins in April with barefoot walking around the room. The daily duration of such walking by the end of May should be 2 hours. At the end of May, you should also start walking or running barefoot on the ground and grass, increasing the daily duration of this procedure to 1 hour during the summer season. do contrasting cold-hot foot baths. Finally, as soon as the first snow falls, you need to start walking on it, gradually increasing the duration to 10 minutes. The authors of this complex argue that everyone who has mastered it is insured against colds. This is explained by a direct reflex connection between the state of the upper respiratory tract and the degree of cooling of the feet, especially pronounced in the winter-spring period.

In 1919, the Komsomol members of Petrograd, at the call of the hygienist Professor V.V. Gorinevsky, who argued that walking barefoot was healthier in the rear, donated their shoes to the Red Army and really walked barefoot all summer.

Interesting results were obtained when examining the health group of the Voronezh central stadium "Trud", where in the second year of hardening they practiced barefoot running on ice and snow for 15 minutes, regardless of the weather. When a leg was immersed in ice water, the veterans of the group experienced an increase in skin temperature on the other leg by 1-2 °, and the temperature was kept at this level for all 5 minutes of cooling. In newcomers, the skin temperature on the control leg after a short-term increase by half a degree fell sharply below the initial level.

Observations made during one of the last US-New Zealand expeditions to the Himalayas testify to what perfection and endurance can be achieved with local cold hardening of the legs. Some of the Sherpa guides made many kilometers along the rocky mountain paths, along the zone of eternal snow ... barefoot. And this is in 20-degree frost!