Message on the topic of jet propulsion in physics. On the way to an outstanding discovery

Among the great technical and scientific achievements of the 20th century, one of the first places undoubtedly belongs to rockets and jet propulsion theory. The years of the Second World War (1941-1945) led to an unusually rapid improvement in the design of jet vehicles. Gunpowder rockets reappeared on the battlefields, but already on more high-calorie smokeless TNT gunpowder (“Katyusha”). Jet-powered aircraft, unmanned aircraft with pulsed air-jet engines ("V-1") and ballistic missiles with a range of up to 300 km ("V-2") were created.

Rocket technology is now becoming a very important and rapidly growing branch of industry. The development of the theory of flight of jet vehicles is one of the pressing problems of modern scientific and technological development.

K. E. Tsiolkovsky did a lot for knowledge fundamentals of the theory of rocket motion. He was the first in the history of science to formulate and investigate the problem of studying rectilinear motions of rockets based on the laws of theoretical mechanics. As we have pointed out, the principle of communicating motion with the help of reaction forces of ejected particles was recognized by Tsiolkovsky as early as 1883, but his creation of a mathematically rigorous theory of jet propulsion dates back to the end of the 19th century.

In one of his works, Tsiolkovsky wrote: “For a long time I looked at the rocket, like everyone else: from the point of view of entertainment and small applications. I don't remember well how it occurred to me to do the calculations related to the rocket. It seems to me that the first seeds of thought were planted by the famous visionary Jules Verne; he awakened my brain in a certain direction. Desires appeared, behind the desires the activity of the mind arose. ... The old sheet with the final formulas related to the jet device is marked with the date August 25, 1898.

“... I never claimed to have a complete solution of the issue. First inevitably come: thought, fantasy, fairy tale. They are followed by scientific calculation. And in the end, the execution crowns the thought. My work on space travel belongs to the middle phase of creativity. More than anyone, I understand the abyss that separates an idea from its implementation, because during my life I have not only thought and calculated, but also executed, also working with my hands. However, it is impossible not to be an idea: the execution is preceded by a thought, an exact calculation is a fantasy.

In 1903, the journal Nauchnoye Obozrenie published Konstantin Eduardovich's first article on rocket technology, which was called "Investigation of world spaces with jet devices." In this work, on the basis of the simplest laws of theoretical mechanics (the law of conservation of momentum and the law of independent action of forces), a theory of rocket flight was given and the possibility of using jet vehicles for interplanetary communications was substantiated (The creation of a general theory of the motion of bodies whose mass changes in the process of motion belongs to Professor I. V. Meshchersky (1859-1935)).

The idea of using a rocket to solve scientific problems, the use of jet engines to create the movement of grandiose interplanetary ships belong entirely to Tsiolkovsky. He is the founder of modern long-range liquid rockets, one of the creators of a new chapter in theoretical mechanics.

Classical mechanics, which studies the laws of motion and equilibrium of material bodies, is based on three laws of motion, clearly and strictly formulated by an English scientist back in 1687. These laws have been used by many researchers to study the motion of bodies whose mass did not change during the motion. Very important cases of motion were considered and a great science was created - the mechanics of bodies of constant mass. The axioms of the mechanics of bodies of constant mass, or Newton's laws of motion, were a generalization of all previous developments in mechanics. At present, the basic laws of mechanical motion are set forth in all physics textbooks for secondary schools. We will give here a summary of Newton's laws of motion, since the next step in science, which made it possible to study the motion of rockets, was a further development of the methods of classical mechanics.

Essay

Physics

On the topic of:

"Jet propulsion"

Completed by a student of the secondary school No. 5

G. Lobnya, 10 "B" class,

Stepanenko Inna Yurievna

Jet propulsion.

For many centuries, mankind has dreamed of space flights. Science fiction writers have proposed a variety of means to achieve this goal. In the 17th century, a story appeared by the French writer Cyrano de Bergerac about a flight to the moon. The hero of this story got to the moon in an iron wagon, over which he constantly threw a strong magnet. Attracted to him, the wagon rose higher and higher above the Earth until it reached the Moon. And Baron Munchausen said that he climbed to the moon on the stalk of a bean.

But not a single scientist, not a single science fiction writer for many centuries has been able to name the only means at the disposal of man, with the help of which one can overcome the force of gravity and fly into space. This was done by the Russian scientist Konstantin Eduardovich Tsiolkovsky (1857-1935). He showed that the only apparatus capable of overcoming gravity is a rocket, i.e. an apparatus with a jet engine using fuel and an oxidizer located on the apparatus itself.

A jet engine is an engine that converts the chemical energy of the fuel into the kinetic energy of a gas jet, while the engine acquires speed in the opposite direction. On what principles and physical laws is its action based?

Everyone knows that a shot from a gun is accompanied by recoil. If the weight of the bullet were equal to the weight of the gun, they would fly apart at the same speed. Recoil occurs because the discarded mass of gases creates a reactive force, due to which movement can be ensured both in air and in airless space. And the greater the mass and speed of the outflowing gases, the greater the recoil force felt by our shoulder, the stronger the reaction of the gun, the greater the reactive force. This can be easily explained from the momentum conservation law, which states that the geometric (i.e. vector) sum of the momenta of the bodies that make up a closed system remains constant for any movements and interactions of the bodies of the system, i.e.

K. E. Tsiolkovsky derived a formula that allows you to calculate the maximum speed that a rocket can develop. Here is the formula:

Here v max is the maximum speed of the rocket, v 0 is the initial speed, v r is the speed of the outflow of gases from the nozzle, m is the initial mass of the fuel, and M is the mass of the empty rocket. As can be seen from the formula, this maximum achievable speed depends primarily on the speed of the outflow of gases from the nozzle, which in turn depends primarily on the type of fuel and the temperature of the gas jet. The higher the temperature, the faster the speed. This means that for a rocket it is necessary to select the most high-calorie fuel that gives the greatest amount of heat. It also follows from the formula that this speed also depends on the initial and final masses of the rocket, i.e. on what part of its weight falls on fuel, and what part - on useless (in terms of flight speed) structures: hull, mechanisms, etc.

This formula of Tsiolkovsky is the foundation on which the entire calculation of modern missiles is based. The ratio of the mass of fuel to the mass of the rocket at the end of the engine operation (ie, essentially to the weight of an empty rocket) is called the Tsiolkovsky number.

The main conclusion from this formula is that in airless space, the rocket will develop the greater the speed, the greater the speed of the outflow of gases and the greater the Tsiolkovsky number.

Conclusion.

On my own behalf, I will add that the description of the operation of an intercontinental ballistic missile that I have given is outdated and corresponds to the level of development of science and technology of the 60s, but, due to limited access to modern scientific materials, I am not able to give an accurate description of the operation of a modern ultra-long-range intercontinental ballistic missile . However, I have highlighted the general properties inherent in all rockets, so I consider my task completed.

List of used literature:

Deryabin V. M. Conservation laws in physics. – M.: Enlightenment, 1982.

Gelfer Ya. M. Conservation laws. – M.: Nauka, 1967.

Body K. World without forms. – M.: Mir, 1976.

Children's encyclopedia. - M .: Publishing house of the USSR Academy of Sciences, 1959.

Essay on Physics On the topic: "Jet propulsion" Completed by a student of the secondary school No. 5 G. Lobnya, 10 "B" class, Stepanenko Inna Yurievna 2006. Reactive movement. For many centuries, mankind has dreamed of space

For many people, the very concept of “jet propulsion” is strongly associated with modern achievements in science and technology, especially physics, and images of jet aircraft or even spacecraft flying at supersonic speeds with the help of the notorious jet engines appear in their heads. In fact, the phenomenon of jet propulsion is much more ancient than even man himself, because it appeared long before us, people. Yes, jet propulsion is actively represented in nature: jellyfish, cuttlefish have been swimming in the depths of the sea for millions of years according to the same principle that modern supersonic jet aircraft fly today.

History of jet propulsion

Since ancient times, various scientists have observed the phenomena of jet propulsion in nature, as the ancient Greek mathematician and mechanic Heron wrote about it before anyone else, however, he never went beyond theory.

If we talk about the practical application of jet propulsion, then the inventive Chinese were the first here. Around the 13th century, they guessed to borrow the principle of movement of octopuses and cuttlefish in the invention of the first rockets, which they began to use both for fireworks and for military operations (as military and signal weapons). A little later, this useful invention of the Chinese was adopted by the Arabs, and from them the Europeans.

Of course, the first conditionally jet rockets had a relatively primitive design and for several centuries they practically did not develop in any way, it seemed that the history of the development of jet propulsion froze. A breakthrough in this matter occurred only in the 19th century.

Who discovered jet propulsion?

Perhaps, the laurels of the discoverer of jet propulsion in the "new time" can be awarded to Nikolai Kibalchich, not only a talented Russian inventor, but also a part-time revolutionary-People's Volunteer. He created his project of a jet engine and an aircraft for people while sitting in a royal prison. Later, Kibalchich was executed for his revolutionary activities, and his project remained gathering dust on the shelves in the archives of the tsarist secret police.

Later, the works of Kibalchich in this direction were discovered and supplemented by the works of another talented scientist, K. E. Tsiolkovsky. From 1903 to 1914, he published a series of papers that convincingly proved the possibility of using jet propulsion in the creation of spacecraft for space exploration. He also formed the principle of using multi-stage rockets. To this day, many of Tsiolkovsky's ideas are used in rocket science.

Examples of jet propulsion in nature

Surely, while swimming in the sea, you saw jellyfish, but you hardly thought that these amazing (and also slow) creatures move just the same thanks to jet propulsion. Namely, by reducing their transparent dome, they squeeze out water, which serves as a kind of “jet engine” for jellyfish.

The cuttlefish also has a similar mechanism of movement - through a special funnel in front of the body and through the side slit, it draws water into its gill cavity, and then vigorously throws it out through the funnel, directed back or to the side (depending on the direction of movement needed by the cuttlefish).

But the most interesting jet engine created by nature is found in squids, which can rightly be called "live torpedoes". After all, even the body of these animals in its form resembles a rocket, although in truth everything is exactly the opposite - this rocket copies the body of a squid with its design.

If the squid needs to make a quick throw, it uses its natural jet engine. Its body is surrounded by a mantle, a special muscle tissue, and half of the volume of the entire squid falls on the mantle cavity, into which it sucks water. Then he abruptly throws out the collected stream of water through a narrow nozzle, while folding all his ten tentacles over his head in such a way as to acquire a streamlined shape. Thanks to such perfect jet navigation, squids can reach an impressive speed of 60-70 km per hour.

Among the owners of a jet engine in nature there are also plants, namely the so-called "mad cucumber". When its fruits ripen, in response to the slightest touch, it shoots gluten with seeds

Law of jet propulsion

Squids, “crazy cucumbers”, jellyfish and other cuttlefish have been using jet propulsion since ancient times, without thinking about its physical essence, but we will try to figure out what the essence of jet propulsion is, what motion is called jet, to give it a definition.

To begin with, you can resort to a simple experiment - if you inflate an ordinary balloon with air and, without tying it, let it fly, it will fly rapidly until it runs out of air. This phenomenon explains Newton's third law, which says that two bodies interact with forces equal in magnitude and opposite in direction.

That is, the force of the impact of the ball on the air flows escaping from it is equal to the force with which the air repels the ball from itself. A rocket also works on a principle similar to a ball, which ejects part of its mass at great speed, while receiving strong acceleration in the opposite direction.

Law of conservation of momentum and jet propulsion

Physics explains the process of jet propulsion. Momentum is the product of a body's mass and its velocity (mv). When a rocket is at rest, its momentum and velocity are zero. When a jet begins to be ejected from it, then the rest, according to the law of conservation of momentum, must acquire such a speed at which the total momentum will still be equal to zero.

Jet propulsion formula

In general, jet propulsion can be described by the following formula:
m s v s +m p v p =0
m s v s =-m p v p

where m s v s is the momentum generated by the jet of gases, m p v p is the momentum received by the rocket.

The minus sign shows that the direction of the rocket and the force of the jet propulsion are opposite.

Jet propulsion in technology - the principle of operation of a jet engine

In modern technology, jet propulsion plays a very important role, as jet engines propel aircraft and spacecraft. The jet engine device itself may differ depending on its size and purpose. But one way or another, each of them has

fuel supply,
chamber, for combustion of fuel,
nozzle, the task of which is to accelerate the jet stream.

This is what a jet engine looks like.

Jet propulsion, video

And finally, an entertaining video about physical experiments with jet propulsion.

Jet propulsion in nature and technology

ABSTRACT ON PHYSICS

Jet propulsion- the movement that occurs when a part of it separates from the body at a certain speed.

The reactive force arises without any interaction with external bodies.

Application of jet propulsion in nature

Many of us in our lives have met while swimming in the sea with jellyfish. In any case, there are enough of them in the Black Sea. But few people thought that jellyfish also use jet propulsion to move around. In addition, this is how dragonfly larvae and some types of marine plankton move. And often the efficiency of marine invertebrates when using jet propulsion is much higher than that of technical inventions.

Jet propulsion is used by many mollusks - octopuses, squids, cuttlefish. For example, a sea scallop mollusk moves forward due to the reactive force of a jet of water ejected from the shell during a sharp compression of its valves.

Octopus

Cuttlefish

The cuttlefish, like most cephalopods, moves in the water in the following way. She takes water into the gill cavity through a lateral slit and a special funnel in front of the body, and then vigorously throws a stream of water through the funnel. The cuttlefish directs the funnel tube to the side or back and, rapidly squeezing water out of it, can move in different directions.

Salpa is a marine animal with a transparent body; when moving, it receives water through the front opening, and the water enters a wide cavity, inside which gills are stretched diagonally. As soon as the animal takes a large sip of water, the hole closes. Then the longitudinal and transverse muscles of the salpa contract, the whole body contracts, and water is pushed out through the rear opening. The reaction of the outflowing jet pushes the salpa forward.

Of greatest interest is the squid jet engine. Squid is the largest invertebrate inhabitant of the ocean depths. Squids have reached the highest level of excellence in jet navigation. They even have a body with its external forms that copies a rocket (or, better, a rocket copies a squid, since it has an indisputable priority in this matter). When moving slowly, the squid uses a large diamond-shaped fin, which periodically bends. For a quick throw, he uses a jet engine. Muscular tissue - the mantle surrounds the body of the mollusk from all sides, the volume of its cavity is almost half the volume of the body of the squid. The animal sucks water into the mantle cavity, and then abruptly ejects a jet of water through a narrow nozzle and moves backward with high speed. In this case, all ten tentacles of the squid are collected in a knot above the head, and it acquires a streamlined shape. The nozzle is equipped with a special valve, and the muscles can turn it, changing the direction of movement. The squid engine is very economical, it is able to reach speeds of up to 60 - 70 km / h. (Some researchers believe that even up to 150 km / h!) It is not for nothing that the squid is called a “living torpedo”. Bending the tentacles folded in a bundle to the right, left, up or down, the squid turns in one direction or another. Since such a steering wheel is very large in comparison with the animal itself, its slight movement is enough for the squid, even at full speed, to easily dodge a collision with an obstacle. A sharp turn of the steering wheel - and the swimmer rushes in the opposite direction. Now he has bent the end of the funnel back and is now sliding head first. He arched it to the right - and the jet thrust threw him to the left. But when you need to swim fast, the funnel always sticks out right between the tentacles, and the squid rushes with its tail forward, as a cancer would run - a runner endowed with the agility of a horse.

If there is no need to hurry, squids and cuttlefish swim, undulating their fins - miniature waves run through them from front to back, and the animal gracefully glides, occasionally pushing itself also with a jet of water thrown out from under the mantle. Then the individual shocks that the mollusk receives at the time of the eruption of water jets are clearly visible. Some cephalopods can reach speeds of up to fifty-five kilometers per hour. No one seems to have made direct measurements, but this can be judged by the speed and range of flying squids. And such, it turns out, there are talents in the relatives of the octopuses! The best pilot among molluscs is the squid stenoteuthis. English sailors call it - flying squid ("flying squid"). This is a small animal the size of a herring. He pursues fish with such swiftness that he often jumps out of the water, rushing over its surface like an arrow. He also resorts to this trick to save his life from predators - tuna and mackerel. Having developed maximum jet thrust in the water, the pilot squid takes off into the air and flies over the waves for more than fifty meters. The apogee of the flight of a living rocket lies so high above the water that flying squids often fall on the decks of ocean-going ships. Four or five meters is not a record height to which squids rise into the sky. Sometimes they fly even higher.

The English shellfish researcher Dr. Rees described in a scientific article a squid (only 16 centimeters long), which, having flown a fair distance through the air, fell on the bridge of the yacht, which towered almost seven meters above the water.

It happens that many flying squids fall on the ship in a sparkling cascade. The ancient writer Trebius Niger once told a sad story about a ship that allegedly even sank under the weight of flying squids that fell on its deck. Squids can take off without acceleration.

Octopuses can also fly. The French naturalist Jean Verany saw an ordinary octopus speed up in an aquarium and suddenly jump out of the water backwards. Describing in the air an arc about five meters long, he plopped back into the aquarium. Gaining speed for the jump, the octopus moved not only due to jet thrust, but also rowed with tentacles.
Baggy octopuses swim, of course, worse than squids, but in critical moments they can show a record class for the best sprinters. California Aquarium staff tried to photograph an octopus attacking a crab. The octopus rushed at prey with such speed that on the film, even when shooting at the highest speeds, there were always lubricants. So, the throw lasted hundredths of a second! Usually octopuses swim relatively slowly. Joseph Signl, who studied octopus migration, calculated that a half-meter octopus swims through the sea at an average speed of about fifteen kilometers per hour. Each jet of water thrown out of the funnel pushes it forward (or rather, back, as the octopus swims backwards) two to two and a half meters.

Jet motion can also be found in the plant world. For example, the ripened fruits of the “mad cucumber” at the slightest touch bounce off the stalk, and a sticky liquid with seeds is ejected with force from the hole formed. The cucumber itself flies in the opposite direction up to 12 m.

Knowing the law of conservation of momentum, you can change your own speed of movement in open space. If you are in a boat and you have some heavy rocks, then throwing rocks in a certain direction will move you in the opposite direction. The same will happen in outer space, but jet engines are used for this.

The use of jet propulsion in technology

At the end of the first millennium AD, China invented jet propulsion that powered rockets - bamboo tubes filled with gunpowder, they were also used as fun. One of the first car projects was also with a jet engine and this project belonged to Newton

The author of the world's first project of a jet aircraft designed for human flight was the Russian revolutionary N.I. Kibalchich. He was executed on April 3, 1881 for participating in the assassination attempt on Emperor Alexander II. He developed his project in prison after the death sentence. Kibalchich wrote: “While in prison, a few days before my death, I am writing this project. I believe in the feasibility of my idea, and this belief supports me in my terrible position ... I will calmly face death, knowing that my idea will not die with me.

The idea of using rockets for space flights was proposed at the beginning of our century by the Russian scientist Konstantin Eduardovich Tsiolkovsky. In 1903, an article by a teacher of the Kaluga gymnasium K.E. Tsiolkovsky "Research of world spaces by jet devices". This work contained the most important mathematical equation for astronautics, now known as the “Tsiolkovsky formula”, which described the motion of a body of variable mass. Subsequently, he developed a scheme for a liquid-fuel rocket engine, proposed a multi-stage rocket design, and expressed the idea of the possibility of creating entire space cities in near-Earth orbit. He showed that the only apparatus capable of overcoming gravity is a rocket, i.e. an apparatus with a jet engine using fuel and an oxidizer located on the apparatus itself.

Jet engine- this is an engine that converts the chemical energy of the fuel into the kinetic energy of the gas jet, while the engine acquires speed in the opposite direction.

The idea of K.E. Tsiolkovsky was carried out by Soviet scientists under the guidance of Academician Sergei Pavlovich Korolev. The first artificial Earth satellite in history was launched by a rocket in the Soviet Union on October 4, 1957.

The principle of jet propulsion finds wide practical application in aviation and astronautics. In outer space there is no medium with which the body could interact and thereby change the direction and modulus of its velocity; therefore, only jet aircraft, i.e., rockets, can be used for space flights.

Rocket device

Rocket motion is based on the law of conservation of momentum. If at some point in time a body is thrown from the rocket, then it will acquire the same momentum, but directed in the opposite direction

In any rocket, regardless of its design, there is always a shell and fuel with an oxidizer. The rocket shell includes a payload (in this case, a spacecraft), an instrument compartment and an engine (combustion chamber, pumps, etc.).

The main mass of the rocket is fuel with an oxidizer (the oxidizer is needed to keep the fuel burning, since there is no oxygen in space).

Fuel and oxidizer are pumped into the combustion chamber. Fuel, burning, turns into a gas of high temperature and high pressure. Due to the large pressure difference in the combustion chamber and in outer space, the gases from the combustion chamber rush out in a powerful jet through a specially shaped bell, called a nozzle. The purpose of the nozzle is to increase the speed of the jet.

Before a rocket launches, its momentum is zero. As a result of the interaction of the gas in the combustion chamber and all other parts of the rocket, the gas escaping through the nozzle receives some impulse. Then the rocket is a closed system, and its total momentum must be equal to zero after launch. Therefore, the shell of the rocket, whatever is in it, receives an impulse equal in absolute value to the impulse of the gas, but opposite in direction.

The most massive part of the rocket, designed to launch and accelerate the entire rocket, is called the first stage. When the first massive stage of a multi-stage rocket exhausts all fuel reserves during acceleration, it separates. Further acceleration is continued by the second, less massive stage, and to the speed previously achieved with the help of the first stage, it adds some more speed, and then separates. The third stage continues to increase its speed to the required value and delivers the payload into orbit.

The first person to fly in outer space was Yuri Alekseevich Gagarin, a citizen of the Soviet Union. April 12, 1961 He circled the globe on the Vostok satellite ship

Soviet rockets were the first to reach the Moon, circled the Moon and photographed its invisible side from the Earth, were the first to reach the planet Venus and delivered scientific instruments to its surface. In 1986, two Soviet spacecraft "Vega-1" and "Vega-2" studied Halley's Comet at close range, approaching the Sun once every 76 years.

The concept of jet propulsion and jet thrust

Jet propulsion (from the point of view, examples in nature)- the movement that occurs when a part of it separates from the body at a certain speed.

The principle of jet propulsion is based on the law of conservation of momentum of an isolated mechanical system of bodies:

That is, the total momentum of a system of particles is a constant value. In the absence of external influences, the momentum of the system is zero and it is possible to change it from the inside due to jet thrust.

Jet thrust (from the point of view, examples in nature)- the reaction force of the separating particles, which is applied at the point of the center of the outflow (for a rocket - the center of the cut of the engine nozzle) and is directed opposite to the velocity vector of the separating particles.

Mass of the working fluid (rockets)

General acceleration of the working body

Expiration rate of separated particles (gases)

Every second fuel consumption

Examples of jet propulsion in inanimate nature

Jet motion can also be found in the plant world. In the southern countries (and here on the Black Sea coast too) a plant called "mad cucumber" grows.

The Latin name of the genus Ecballium comes from the Greek word with the meaning - I throw out, according to the structure of the fruit that throws out the seeds.

The fruits of a mad cucumber are bluish-green or green, juicy, oblong or oblong-ovate, 4–6 cm long, 1.5–2.5 wide, bristly, blunt at both ends, multi-seeded (Fig. 1). Seeds are elongated, small, compressed, smooth, narrowly bordered, about 4 mm long. When the seeds ripen, the tissue surrounding them turns into a slimy mass. At the same time, a lot of pressure is formed in the fruit, as a result of which the fruit is separated from the stalk, and the seeds, together with the mucus, are thrown out with force through the hole formed. The cucumbers themselves fly off in the opposite direction. Shoots a mad cucumber (otherwise it is called a "lady's pistol") more than 12 m (Fig. 2).

Examples of jet propulsion in the animal kingdom

Sea creatures

Many marine animals use jet propulsion to move around, including jellyfish, scallops, octopuses, squids, cuttlefish, salps, and some types of plankton. All of them use the reaction of an ejected jet of water, the difference lies in the structure of the body, and therefore in the method of intake and ejection of water.

The sea scallop mollusk (Fig. 3) moves due to the reactive force of the water jet ejected from the shell during a sharp compression of its valves. He applies this kind of movement in case of danger.

Cuttlefish (Figure 4) and octopuses (Figure 5) take water into the gill cavity through a lateral slit and a special funnel in front of the body, and then vigorously eject a stream of water through the funnel. The cuttlefish directs the funnel tube to the side or back and, rapidly squeezing water out of it, can move in different directions. Octopuses, folding their tentacles over their heads, give their body a streamlined shape and can thus control their movement, changing its direction.

Octopuses can even fly. The French naturalist Jean Verany saw an ordinary octopus speed up in an aquarium and suddenly jump out of the water backwards. Describing in the air an arc about five meters long, he plopped back into the aquarium. Gaining speed for the jump, the octopus moved not only due to jet thrust, but also rowed with tentacles.

Salpa (Fig. 6) is a marine animal with a transparent body; when moving, it receives water through the front opening, and the water enters a wide cavity, inside which the gills are stretched diagonally. As soon as the animal takes a large sip of water, the hole closes. Then the longitudinal and transverse muscles of the salpa contract, the whole body contracts and water is pushed out through the rear opening.

Squid (Figure 7). Muscular tissue - the mantle surrounds the body of the mollusk from all sides, the volume of its cavity is almost half the volume of the body of the squid. The animal sucks water into the mantle cavity, and then abruptly ejects a jet of water through a narrow nozzle and moves backward with high speed. In this case, all ten tentacles of the squid are collected in a knot above the head, and it acquires a streamlined shape. The nozzle is equipped with a special valve, and the muscles can turn it, changing the direction of movement. The squid engine is very economical and is capable of speeds up to 60 - 70 km / h. Bending the tentacles folded in a bundle to the right, left, up or down, the squid turns in one direction or another. Since such a steering wheel is very large in comparison with the animal itself, its slight movement is enough for the squid, even at full speed, to easily dodge a collision with an obstacle. But when you need to swim fast, the funnel always sticks out right between the tentacles, and the squid rushes with its tail forward.

Engineers have already created an engine similar to a squid engine. It's called a water jet. In it, water is sucked into the chamber. And then it is thrown out of it through a nozzle; the vessel moves in the direction opposite to the direction of jet ejection. Water is sucked in using a conventional petrol or diesel engine (see Appendix).

The best pilot among mollusks is the squid stenoteuthis. Sailors call it - "flying squid". He pursues fish with such swiftness that he often jumps out of the water, rushing over its surface like an arrow. He also resorts to this trick to save his life from predators - tuna and mackerel. Having developed maximum jet thrust in the water, the pilot squid takes off into the air and flies over the waves for more than fifty meters. The apogee of the flight of a living rocket lies so high above the water that flying squids often fall on the decks of ocean-going ships. Four or five meters is not a record height to which squids rise into the sky. Sometimes they fly even higher.

Insects

Dragonfly larvae also move in a similar way. And not all, but long-bellied, actively swimming larvae of stagnant (family Rocker) and flowing (family Cordulegaster) waters, as well as short-bellied crawling larvae of stagnant waters. The larva uses jet movement mainly in a moment of danger in order to quickly move to another place. This method of movement does not provide for precise maneuvering and is not suitable for chasing prey. But the rocker larvae do not chase anyone - they prefer hunting from an ambush.

The hindgut of the dragonfly larva, in addition to its main function, also performs the role of an organ of movement. Water fills the hindgut, then it is thrown out with force, and the larva moves according to the principle of jet propulsion by 6-8 cm.

jet propulsion nature technique

Application