For many people, the very concept of “jet propulsion” is strongly associated with modern achievements in science and technology, especially physics, and images appear in their heads jet aircraft or even spacecraft flying at supersonic speeds with the help of the proverbial jet engines. 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 practical application jet propulsion, 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 pioneer 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. Your jet engine project and aircraft for people he created while sitting in the 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 ejects 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, “mad 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, spaceships. 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.

The use of jet propulsion in nature Many of us in our lives have met while swimming in the sea with jellyfish. But few people thought that jellyfish also use jet propulsion to move around. And often the efficiency of marine invertebrates when using jet propulsion is much higher than that of techno inventions.

Cuttlefish 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.

Squid The squid is the largest invertebrate inhabitant of the ocean depths. It moves according to the principle of jet propulsion, absorbing water into itself, and then pushing it with great force through a special hole - a "funnel", and at high speed (about 70 km / h) moves back in jolts. In this case, all ten tentacles of the squid are collected in a knot above the head and it acquires a streamlined shape.

Flying squid This is a small animal about 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. 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.

Octopus 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.

Crazy Cucumber In the southern countries (and here on the Black Sea coast too) a plant called "Crazy Cucumber" grows. One has only to lightly touch the ripe fruit, similar to a cucumber, as it bounces off the stalk, and liquid with seeds flies out of the fruit at a speed of up to 10 m / s through the hole formed. Shoots a mad cucumber (otherwise it is called a "lady's pistol") more than 12 m.

The logic of nature is the most accessible and most useful logic for children.

Konstantin Dmitrievich Ushinsky(03/03/1823–01/03/1871) - Russian teacher, founder of scientific pedagogy in Russia.

BIOPHYSICS: JET PROMOTION IN LIVING NATURE

I suggest readers of the green pages to look into the fascinating world of biophysics and get to know the main principles of jet propulsion in wildlife. Today's program: jellyfish cornerot- the largest jellyfish in the Black Sea, scallops, enterprising dragonfly larva, delicious squid with its unrivaled jet engine and wonderful illustrations by the Soviet biologist and animal painter Kondakov Nikolai Nikolaevich.

According to the principle of jet propulsion in wildlife, a number of animals move, for example, jellyfish, scallops, larvae of the rocker dragonfly, squid, octopus, cuttlefish ... Let's get to know some of them better ;-)

Jet way of moving jellyfish

Jellyfish are one of the most ancient and numerous predators on our planet! The body of a jellyfish is 98% water and is largely composed of watered connective tissue - mesoglea functioning like a skeleton. The basis of mesoglea is the protein collagen. The gelatinous and transparent body of a jellyfish is shaped like a bell or an umbrella (in diameter from a few millimeters up to 2.5 m). Most jellyfish move reactive way pushing water out of the cavity of the umbrella.

Jellyfish Cornerota(Rhizostomae), a detachment of coelenterates of the scyphoid class. Jellyfish ( up to 65 cm in diameter) are devoid of marginal tentacles. The edges of the mouth are elongated into oral lobes with numerous folds that grow together to form many secondary oral openings. Touching the mouth lobes can cause painful burns due to the action of stinging cells. About 80 species; They live mainly in tropical, less often in temperate seas. In Russia - 2 types: Rhizostoma pulmo common in the Black and Azov seas, Rhopilema asamushi found in the Sea of ​​Japan.

Jet escape sea scallop clams

Sea shellfish scallops, usually lying quietly at the bottom, when their main enemy approaches them - a delightfully slow, but extremely insidious predator - starfish- sharply squeeze the valves of their shell, pushing water out of it with force. Thus using jet propulsion principle, they float up and, continuing to open and close the shell, can swim a considerable distance. If, for some reason, the scallop does not have time to escape with its jet flight, starfish grabs it with her hands, opens the shell and eats it ...

Scallop(Pecten), a genus of marine invertebrates in the class of bivalves (Bivalvia). The scallop shell is rounded with a straight hinge edge. Its surface is covered with radial ribs diverging from the top. The shell valves are closed by one strong muscle. Pecten maximus, Flexopecten glaber live in the Black Sea; in the Sea of ​​Japan and the Sea of ​​Okhotsk - Mizuhopecten yessoensis ( up to 17 cm in diameter).

Rocker dragonfly jet pump

temperament dragonfly larvae, or ashny(Aeshna sp.) no less predatory than its winged relatives. For two, and sometimes four years, she lives in the underwater kingdom, crawls along the rocky bottom, tracking down small aquatic inhabitants, with pleasure including rather large-caliber tadpoles and fry in her diet. In moments of danger, the larva of the dragonfly-rocker takes off and jerks forward, driven by the work of a wonderful jet pump. Taking water into the hindgut and then abruptly throwing it out, the larva jumps forward, driven by the recoil force. Thus using jet propulsion principle, the larva of the rocker dragonfly hides from the threat pursuing it with confident jerks and jerks.

Reactive impulses of the nervous "freeway" of squids

In all the above cases (principles of the jet propulsion of jellyfish, scallops, larvae of the rocker dragonfly), pushes and jerks are separated from each other by significant intervals of time, therefore, a high speed of movement is not achieved. To increase the speed of movement, in other words, number of reactive impulses per unit time, needed increased nerve conduction that excite muscle contraction, serving a living jet engine. Such a large conductivity is possible with a large diameter of the nerve.

It is known that squid have the largest nerve fibers in the animal kingdom. On average, they reach 1 mm in diameter - 50 times larger than most mammals - and they conduct excitation at a speed 25 m/s. And a three-meter squid dosidicus(he lives off the coast of Chile) the thickness of the nerves is fantastically large - 18 mm. Nerves as thick as ropes! The signals of the brain - the causative agents of contractions - rush along the nervous "freeway" of the squid at a speed passenger car – 90 km/h.

Thanks to squid, research on the vital activity of nerves has advanced rapidly since the early 20th century. "And who knows, writes the British naturalist Frank Lane, maybe there are now people who owe the squid that their nervous system is in a normal state ... "

The speed and maneuverability of the squid is also explained by the excellent hydrodynamic forms animal body, why squid and nicknamed "live torpedo".

squids(Teuthoidea), a suborder of cephalopods of the decapod order. The size is usually 0.25-0.5 m, but some species are the largest invertebrates(squids of the genus Architeuthis reach 18 m, including the length of the tentacles).
The body of squids is elongated, pointed at the back, torpedo-shaped, which determines the high speed of their movement as in water ( up to 70 km/h), and in the air (squids can jump out of the water to a height up to 7 m).

Squid jet engine

Jet propulsion , now used in torpedoes, aircraft, rockets and space projectiles, is also characteristic cephalopods - octopus, cuttlefish, squid. Of greatest interest to technicians and biophysicists is squid jet engine. Pay attention to how simply, with what minimal material consumption, nature solved this complex and still unsurpassed task ;-)

In essence, the squid has two fundamentally different engines ( rice. 1a). When moving slowly, it uses a large diamond-shaped fin, periodically bending in the form of a traveling wave along the body. The squid uses a jet engine to throw itself quickly.. The basis of this engine is the mantle - muscle tissue. It surrounds the body of the mollusk from all sides, making up almost half of the volume of its body, and forms a kind of reservoir - mantle cavity - the "combustion chamber" of a living rocket into which water is periodically sucked. The mantle cavity contains the gills and internal organs of the squid ( rice. 1b).

With a jet way of swimming the animal sucks water through the wide open mantle fissure into the mantle cavity from the boundary layer. The mantle gap is tightly “fastened” with special “button cufflinks” after the “combustion chamber” of a living engine is filled with sea water. The mantle gap is located near the middle of the squid body, where it has the greatest thickness. The force that causes the movement of the animal is created by ejecting a jet of water through a narrow funnel, which is located on the abdominal surface of the squid. This funnel, or siphon, - "nozzle" of a living jet engine.

The "nozzle" of the engine is equipped with a special valve and the muscles can turn it. By changing the installation angle of the funnel-nozzle ( rice. 1c), the squid swims equally well both forward and backward (if it swims backward, the funnel extends along the body, and the valve is pressed against its wall and does not interfere with the water jet flowing from the mantle cavity; when the squid needs to move forward, the free end of the funnel somewhat elongates and bends in the vertical plane, its outlet is folded and the valve assumes a bent position). Jet thrusts and the suction of water into the mantle cavity follow one after another with imperceptible speed, and the squid rockets through the blue of the ocean like a rocket.

Squid and its jet engine - figure 1

1a) squid - live torpedo; 1b) squid jet engine; 1c) the position of the nozzle and its valve when the squid moves back and forth.

The animal spends fractions of a second on the intake of water and its expulsion. By sucking water into the mantle cavity in the stern part of the body during periods of slow motion by inertia, the squid thereby performs suction of the boundary layer, thus preventing flow separation during unsteady flow around. By increasing the portions of ejected water and increasing the contraction of the mantle, the squid easily increases the speed of movement.

The squid jet engine is very economical, so that it can reach the speed 70 km/h; some researchers believe that even 150 km/h!

Engineers have already created engine similar to squid jet engine: this is water cannon operating with a conventional gasoline or diesel engine. Why squid jet engine still attracts the attention of engineers and is the object of careful research by biophysicists? For work under water, it is convenient to have a device that works without access to atmospheric air. The creative search of engineers is aimed at creating a design hydrojet engine, similar air-jet…

Based on great books:
"Biophysics at physics lessons" Cecilia Bunimovna Katz,
and "Primates of the Sea" Igor Ivanovich Akimushkina

Kondakov Nikolai Nikolaevich (1908–1999) – Soviet biologist, animal painter, candidate of biological sciences. His main contribution to biological science was his drawings of various representatives of the fauna. These illustrations have been included in many publications, such as Great Soviet Encyclopedia, Red Book of the USSR, in animal atlases and teaching aids.

Akimushkin Igor Ivanovich (01.05.1929–01.01.1993) – Soviet biologist, writer - popularizer of biology, author of popular science books about animal life. Laureate of the All-Union Society "Knowledge" award. Member of the Writers' Union of the USSR. The most famous publication of Igor Akimushkin is a six-volume book "Animal world".

The materials of this article will be useful to apply not only in physics lessons and biology but also in extracurricular activities.
Biophysical material is extremely beneficial for mobilizing the attention of students, for turning abstract formulations into something concrete and close, affecting not only the intellectual, but also the emotional sphere.

Literature:
§ Katz Ts.B. Biophysics at physics lessons

§ § Akimushkin I.I. Primates of the sea
Moscow: publishing house "Thought", 1974
§ Tarasov L.V. Physics in nature
Moscow: Enlightenment publishing house, 1988

Ministry of Education and Science of the Russian Federation
FGOU SPO "Perevozsky Construction College"
abstract
discipline:
Physics
topic: Jet propulsion

Completed:
Student
Groups 1-121
Okuneva Alena
Checked:
P.L. Vineaminovna

City Perevoz
2011
Content:

Introduction: What is Jet Propulsion…………………………………………………………………………………………………………..3
Law of conservation of momentum…………………………………………………………………….4
Application of jet propulsion in nature…………………………..….…....5
The use of jet propulsion in technology…….…………………...…..….….6
Jet propulsion "Intercontinental missile"…………..………...…7
The physical basis of the jet engine..................... .................... 8
Classification of jet engines and features of their use……………………………………………………………………….………….…….9
Features of the design and creation of an aircraft…..…10
Conclusion………………………………………………………………………………………………….11
List of used literature…………………………………………………………..12

"Jet propulsion"
Jet motion - the movement of a body due to the separation from it with a certain speed of some part of it. Jet motion is described based on the law of conservation of momentum.
Jet propulsion, which is now used in airplanes, rockets and space projectiles, is characteristic of octopuses, squids, cuttlefish, jellyfish - all of them, without exception, use the reaction (recoil) of an ejected jet of water to swim.
Examples of jet propulsion can also be found in the plant world.
In southern countries, a plant called "mad cucumber" grows. One has only to lightly touch the ripe fruit, similar to a cucumber, as it bounces off the stalk, and through the hole formed from the fruit, liquid with seeds flies out at a speed of up to 10 m / s.

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.

"Law of Conservation of Momentum"
In a closed system, the vector sum of the impulses of all bodies included in the system remains constant for any interactions of the bodies of this system with each other.
This fundamental law of nature is called the law of conservation of momentum. It is a consequence of Newton's second and third laws. Consider two interacting bodies that are part of a closed system.
The forces of interaction between these bodies will be denoted by and According to Newton's third law If these bodies interact during time t, then the impulses of the interaction forces are identical in absolute value and directed in opposite directions: Let's apply Newton's second law to these bodies:

This equality means that as a result of the interaction of two bodies, their total momentum has not changed. Considering now all possible pair interactions of bodies included in a closed system, we can conclude that the internal forces of a closed system cannot change its total momentum, i.e., the vector sum of the momenta of all bodies included in this system. A significant reduction in the launch mass of the rocket can be achieved by usingmulti-stage rocketswhen the rocket stages separate as the fuel burns out. Masses of containers containing fuel, spent engines, control systems, etc. are excluded from the process of subsequent rocket acceleration. It is along the path of creating economical multi-stage rockets that modern rocket science is developing.

"Application of jet propulsion in nature"
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
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 takes 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. 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 that copies a rocket with its external forms. 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.

"Application of jet propulsion in technology"
At the end of the first millennium of our era, jet propulsion was invented in China, which powered rockets - bamboo tubes filled with gunpowder, they were also used as fun. One of the first car designs 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 rocket engine on liquid fuel, proposed a multi-stage rocket design, 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. 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.

Jet propulsion "Intercontinental missile"
Mankind has always dreamed of traveling into space. A variety of means to achieve this goal were offered by writers - science fiction, scientists, dreamers. But for many centuries, not a single scientist, not a single science fiction writer could invent the only means at the disposal of man, with the help of which it is possible to overcome the force of gravity and fly into space. K. E. Tsiolkovsky is the founder of the theory of space flights.
For the first time, the dream and aspirations of many people for the first time could be brought closer to reality by the Russian scientist Konstantin Eduardovich Tsiolkovsky (1857-1935), who showed that the only device capable of overcoming gravity is a rocket, he first presented scientific proof of the possibility of using a rocket to fly into outer space , beyond the earth's atmosphere and to other planets solar system. Tsoilkovsky called a rocket an apparatus with a jet engine that uses the fuel and oxidizer on it.
As you know from the course of physics, a shot from a gun is accompanied by recoil. According to Newton's laws, a bullet and a gun would scatter in different directions with the same speed if they had the same mass. The discarded mass of gases creates a reactive force, due to which movement can be ensured both in air and in airless space, this is how recoil occurs. The greater the recoil force felt by our shoulder, the greater the mass and speed of the outflowing gases, and, consequently, the stronger the reaction of the gun, the greater the reactive force. These phenomena are explained by the law of conservation of momentum:
the vector (geometric) sum of the impulses of the bodies that make up a closed system remains constant for any movements and interactions of the bodies of the system.
The presented formula of Tsiolkovsky is the foundation on which the entire calculation of modern missiles is based. The Tsiolkovsky number is the ratio of the mass of fuel to the mass of the rocket at the end of engine operation - to the weight of an empty rocket.
Thus, it was found that the maximum achievable speed of the rocket depends primarily on the speed of the outflow of gases from the nozzle. And the rate of outflow of gases from the nozzle, in turn, depends on the type of fuel and the temperature of the gas jet. So the higher the temperature, the faster the speed. Then for a real rocket you need to choose the most high-calorie fuel that gives the greatest amount of heat. The formula shows that, among other things, the speed of a rocket depends on the initial and final mass of the rocket, on what part of its weight falls on fuel, and what part - on useless (in terms of flight speed) structures: body, mechanisms, etc. d.
The main conclusion from this Tsiolkovsky formula for determining the speed of a space rocket 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 number of Tsiolkovsky.

"Physical foundations of the jet engine"
At the heart of modern powerful jet engines different types lies the principle of direct reaction, i.e. the principle of creating a driving force (or thrust) in the form of a reaction (recoil) of a jet of "working substance" flowing out of the engine, usually hot gases. In all engines, there are two processes of energy conversion. First, the chemical energy of the fuel is converted into thermal energy of the combustion products, and then the thermal energy is used to perform mechanical work. Such engines include reciprocating engines of automobiles, diesel locomotives, steam and gas turbines of power plants, etc. After hot gases have formed in the heat engine, containing large thermal energy, this energy must be converted into mechanical energy. After all, the purpose of the engines is to perform mechanical work, to "move" something, to put it into action, it doesn't matter whether it is a dynamo at the request to supplement the drawings of a power plant, a diesel locomotive, a car or an airplane. In order for the thermal energy of gases to be converted into mechanical energy, their volume must increase. With such an expansion, the gases do the work for which their internal and thermal energy is expended.
The jet nozzle can have various shapes, and, moreover, a different design, depending on the type of engine. The main thing is the speed with which the gases flow out of the engine. If this outflow velocity does not exceed the speed with which sound waves propagate in the outflowing gases, then the nozzle is a simple cylindrical or narrowing pipe section. If the outflow velocity must exceed the speed of sound, then the nozzle is given the shape of an expanding pipe or, first, narrowing, and then expanding (Love's nozzle). Only in a tube of such a shape, as theory and experience show, is it possible to disperse the gas to supersonic speeds, to step over the "sonic barrier".

"Classification of jet engines and features of their use"
However, this mighty trunk, the principle of direct reaction, gave life to a huge crown of the "family tree" of the family of jet engines. To get acquainted with the main branches of its crown, crowning the "trunk" of the direct reaction. Soon, as can be seen from the figure (see below), this trunk is divided into two parts, as if split by a lightning strike. Both new trunks are equally decorated with mighty crowns. This division occurred due to the fact that all "chemical" jet engines are divided into two classes, depending on whether they use ambient air for their work or not.
In a compressorless engine of another type, a ramjet, there is not even this valve grid and the pressure in the combustion chamber rises as a result of the velocity pressure, i.e. deceleration of the oncoming air flow entering the engine in flight. It is clear that such an engine is able to work only when the aircraft is already flying at a sufficiently high speed, it will not develop thrust in the parking lot. But on the other hand, at a very high speed, 4-5 times the speed of sound, a ramjet develops very high thrust and consumes less fuel than any other "chemical" jet engine under these conditions. That's why ramjet motors.
etc.................