Great importance the law of conservation of momentum has when considering jet propulsion.
Under jet propulsion understand the movement of a body that occurs when a certain part of it is separated at a certain speed relative to it, for example, when combustion products flow out of the nozzle of a jet aircraft. This gives rise to the so-called Reactive force pushing the body.
The peculiarity of the reactive force is that it arises as a result of the interaction between the parts of the system itself without any interaction with external bodies.
While the force imparting acceleration, for example, to a pedestrian, a ship or an airplane, arises only due to the interaction of these bodies with earth, water or air.
So the motion of the body can be obtained as a result of the outflow of a jet of liquid or gas.
In nature, jet propulsion inherent mainly in living organisms living in the aquatic environment.
In technology, jet propulsion is used in river transport (jet engines), in the automotive industry (racing cars), in military affairs, in aviation and astronautics.
All modern high-speed aircraft are equipped with jet engines, because. they are able to provide the required flight speed.
In outer space, it is impossible to use other engines, except for jet engines, since there is no support, starting from which one could get acceleration.
History of the development of jet technology
The creator of the Russian combat missile was the artillery scientist K.I. Konstantinov. With a weight of 80 kg, the range of the Konstantinov rocket reached 4 km.
The idea of using jet propulsion in an aircraft, the project of a jet aeronautical instrument, was put forward in 1881 by N.I. Kibalchich.
In 1903, the famous physicist K.E. Tsiolkovsky proved the possibility of flight in interplanetary space and developed the project of the first rocket plane with a liquid-propellant engine.
K.E. Tsiolkovsky designed a space rocket train, made up of a number of rockets that work in turn and fall off as fuel is used up.
Principles for the use of jet engines
The basis of any jet engine is the combustion chamber, in which, during the combustion of fuel, gases are formed that have a very high temperature and exert pressure on the walls of the chamber. Gases escape from the narrow nozzle of the rocket at high speed and create jet thrust. According to the law of conservation of momentum, the rocket gains speed in the opposite direction.
The momentum of the system (rocket-combustion products) remains equal to zero. Since the mass of the rocket is decreasing, even with constant speed the outflow of gases, its speed will increase, gradually reaching a maximum value.
Rocket motion is an example of the motion of a body with a variable mass. To calculate its speed, the law of conservation of momentum is used.
Jet engines are divided into rocket engines and jet engines.
rocket engines available in solid or liquid fuels.
In solid propellant rocket engines, a propellant containing both fuel and an oxidizer will be placed inside the combustion chamber of the engine.
AT liquid-propellant engines, designed to launch spacecraft, fuel and oxidizer are stored separately in special tanks and pumped into the combustion chamber. Kerosene, gasoline, alcohol, liquid hydrogen, etc. can be used as fuel in them, and liquid oxygen, nitric acid, etc., can be used as an oxidizing agent necessary for combustion.
Modern three-stage space rockets are launched vertically, and after passing through the dense layers of the atmosphere, they are transferred to a flight in a given direction. Each rocket stage has its own fuel tank and oxidizer tank, as well as its own jet engine. As the fuel burns, the spent rocket stages are discarded.
Air jet engines currently used mainly in aircraft. Their main difference from rocket engines is that the oxidizer for fuel combustion is the oxygen of the air entering the engine from the atmosphere.
Jet engines include turbocompressor engines with both axial and centrifugal compressors.
The air in such engines is sucked in and compressed by a compressor driven by a gas turbine. The gases leaving the combustion chamber create a thrust force and rotate the turbine rotor.
At very high flight speeds, the compression of gases in the combustion chamber can be carried out due to the oncoming air flow. The need for a compressor is eliminated.
Today, most people, of course, associate jet propulsion primarily with the latest scientific and technical developments. From textbooks on physics, we know that by "reactive" they mean the movement that occurs as a result of separation from an object (body) of any of its parts. A man wanted to rise into the sky to the stars, he strove to fly, but he could fulfill his dream only with the advent of jet aircraft and stepped spacecraft capable of traveling great distances, accelerating to supersonic speeds, thanks to modern jet engines installed on them. Designers and engineers developed the possibility of using jet propulsion in engines. Fantasts also did not stand aside, offering the most incredible ideas and ways to achieve this goal. Surprisingly, this principle of movement is widespread in wildlife. It is enough to look around, you can notice the inhabitants of the seas and land, among which there are plants, the basis of which is the reactive principle.
Story
Even in ancient times, scientists with interest studied and analyzed the phenomena associated with jet propulsion in nature. One of the first who theoretically substantiated and described its essence was Heron, a mechanic and theorist Ancient Greece who invented the first steam engine named after him. The Chinese were able to find a reactive method practical use. They were the first, taking as a basis the method of movement of cuttlefish and octopuses, back in the 13th century they invented rockets. They were used in fireworks, making a big impression, and also as flares, there may have been live rockets that were used as rocket artillery. Over time, this technology came to Europe.
N. Kibalchich became the discoverer of the new time, having invented a scheme for a prototype aircraft with a jet engine. He was an outstanding inventor and a convinced revolutionary, for which he was in prison. It was while in prison that he made history by creating his project. After his execution for active revolutionary activity and speaking out against the monarchy, his invention was forgotten on the archive shelves. Some time later, K. Tsiolkovsky was able to improve the ideas of Kibalchich, proving the possibility of exploring outer space through the jet movement of spacecraft.
Later, during the Great Patriotic War, the famous Katyushas, field rocket artillery systems, appeared. So affectionate name the people unofficially called the powerful installations that the forces of the USSR used. It is not known for certain, in connection with which, the weapon received this name. The reason for this was either the popularity of Blanter's song, or the letter "K" on the body of the mortar. Over time, the front-line soldiers began to give nicknames to other weapons, thus creating a new tradition. The Germans, on the other hand, called this combat rocket launcher "Stalin's organ" for its appearance, which resembled musical instrument and the shrill sound that came from launching rockets.
Vegetable world
Representatives of the fauna also use the laws of jet propulsion. Most plants with such properties are annuals and juveniles: prickly, petiolate garlic, heart touchy, double-cut pikulnik, three-veined mehringia.
Prickly, otherwise mad cucumber, belongs to the gourd family. This plant reaches large sizes, has a thick root with a rough stem and large leaves. It grows in the territory of Central Asia, the Mediterranean, the Caucasus, is quite common in the south of Russia and Ukraine. Inside the fruit, during the ripening period, the seeds are converted into mucus, which, under the influence of temperatures, begins to ferment and release gas. Closer to ripening, the pressure inside the fetus can reach 8 atmospheres. Then, with a light touch, the fruit breaks off from the base and the seeds with liquid fly out of the fruit at a speed of 10 m/s. Due to the ability to shoot at 12 m in length, the plant was called the "lady's gun".
The heart of the touchy is an annual widespread species. It is found, as a rule, in shady forests, along the banks along rivers. Once in the northeastern part of North America and in South Africa, settled down successfully. The touchy heart is propagated by seeds. The seeds at the touchy core are small, weighing no more than 5 mg, which are thrown to a distance of 90 cm. Thanks to this method of seed distribution, the plant got its name.
Animal world
Jet propulsion - interesting facts about the animal world. In cephalopods, reactive movement occurs through water exhaled through a siphon, which usually narrows to a small opening to obtain maximum exhalation velocity. Water passes through the gills before exhalation, fulfilling the dual purpose of respiration and locomotion. Sea hares, otherwise gastropods, use similar means movements, but without the complex neurological apparatus of cephalopods, they move more clumsily.
Some knightfish have also evolved jet propulsion by passing water over their gills to supplement their fin propulsion.
In dragonfly larvae, reactive power is achieved by displacing water from a specialized cavity in the body. Scallops and cardids, siphonophores, tunics (such as salps), and some jellyfish also use jet propulsion.
Most of the time, scallops lie quietly on the bottom, but in case of danger, they quickly close the valves of their shells, so they push out the water. This behavior mechanism also speaks of the use of the principle of jet displacement. Thanks to him, the scallops can float up and move a long distance using the shell opening-closing technique.
The squid also uses this method, absorbing water, and then pushing it through the funnel with great force, it moves at a speed of at least 70 km / h. Gathering the tentacles into one knot, the body of the squid forms a streamlined shape. Taking such a squid engine as a basis, the engineers designed a water cannon. The water in it is sucked into the chamber, and then thrown out through the nozzle. So the ship is heading for reverse side from the ejected jet.
Compared to squids, salps use the most efficient engines, spending an order of magnitude less energy than squids. When moving, the salpa launches water into the hole in front, and then enters a wide cavity where the gills are stretched. After a sip, the hole closes, and with the help of contracting longitudinal and transverse muscles that compress the body, water is ejected through the hole from behind.
The most unusual of all the mechanisms of movement boasts an ordinary cat. Marcel Desprez suggested that the body is able to move and change its position even with the help of internal forces alone (without repelling or relying on anything), from which it could be concluded that Newton's laws could be wrong. The proof of his assumption could serve as a cat that fell from a height. During the fall upside down, she will still land on all her paws, this has already become a kind of axiom. Having photographed in detail the movement of the cat, we were able to see everything that she was doing in the air frame by frame. We saw her movement with her paw, which caused a response of the body, turning in the opposite direction relative to the movement of the paw. Acting according to Newton's laws, the cat landed successfully.
In animals, everything happens at the level of instinct, a person, in turn, does it consciously. Professional swimmers, having jumped from the tower, have time to turn around three times in the air, and having managed to stop the rotation, they straighten up strictly vertically and dive into the water. The same principle applies to aerial circus gymnasts.
No matter how much a person tries to surpass nature by improving the inventions created by it, anyway, we have not yet reached that technological perfection when airplanes could repeat the actions of a dragonfly: hover in the air, instantly move back or move to the side. And all this happens at high speed. Perhaps a little more time will pass and the aircraft, thanks to corrections for the characteristics of aerodynamics and the reactive capabilities of dragonflies, will be able to make sharp turns and become less susceptible to external conditions. Having peeped from nature, a person can still improve a lot for the benefit of technical progress.
Multi-ton spaceships soar into the sky, and in sea waters transparent, gelatinous jellyfish, cuttlefish and octopuses deftly maneuver - what do they have in common? It turns out that in both cases, the principle of jet propulsion is used to move. It is this topic that our today's article is devoted to.
Let's look into history
Most The first reliable information about rockets dates back to the 13th century. They were used by Indians, Chinese, Arabs and Europeans in combat operations as military and signal weapons. Then followed centuries of almost complete oblivion of these devices.
In Russia, the idea of using a jet engine was revived thanks to the work of the Narodnaya Volya revolutionary Nikolai Kibalchich. Sitting in the royal dungeons, he developed the Russian project of a jet engine and an aircraft for people. Kibalchich was executed, and his project long years gathering dust in the archives of the tsarist secret police.
The main ideas, drawings and calculations of this talented and courageous person received further development in the works of K. E. Tsiolkovsky, who proposed using them for interplanetary communications. From 1903 to 1914, he published a number of works, where he convincingly proves the possibility of using jet propulsion to explore outer space and substantiates the feasibility of using multi-stage rockets.
Many scientific developments of Tsiolkovsky are still used in rocket science.
biological missiles
How did it come about the idea of moving by pushing off your own jet stream? Perhaps, closely watching the marine life, the inhabitants of the coastal zones noticed how this happens in the animal world.
For example, scallop moves due to the reactive force of the water jet ejected from the shell during the rapid compression of its valves. But he will never keep up with the fastest swimmers - squids.
Their rocket-shaped bodies rush tail forward, throwing out stored water from a special funnel. move according to the same principle, squeezing out water by contracting their transparent dome.
Nature endowed a "jet engine" and a plant called "squirting cucumber". When its fruits are fully ripe, in response to the slightest touch, it shoots out gluten with seeds. The fetus itself is thrown in the opposite direction at a distance of up to 12 m!
Neither marine life nor plants know the physical laws underlying this mode of locomotion. We'll try to figure this out.
Physical foundations of the principle of jet propulsion
Let's start with a simple experiment. Inflate a rubber ball and, without tying, we will let go into free flight. The rapid movement of the ball will continue as long as the stream of air flowing from it is strong enough.
To explain the results of this experience, we should turn to the third law, which states that two bodies interact with forces equal in magnitude and opposite in direction. Therefore, the force with which the ball acts on the jets of air escaping from it is equal to the force with which the air repels the ball from itself.
Let's transfer this reasoning to the rocket. These devices at great speed throw out some of their mass, as a result of which they themselves receive acceleration in the opposite direction.
From a physics point of view, this the process is clearly explained by the law of conservation of momentum. Momentum is the product of the body's mass and its velocity (mv) While the rocket is at rest, its velocity and momentum are zero. If a jet stream is ejected from it, then the remaining part, according to the law of conservation of momentum, must acquire such a speed that the total momentum is still equal to zero.
Let's look at the formulas:
m g v g + m p v p =0;
m g v g \u003d - m p v p,
where m g v g the momentum created by the jet of gases, m p v p the momentum received by the rocket.
The minus sign shows that the direction of movement of the rocket and the jet stream are opposite.
The device and principle of operation of a jet engine
In technology, jet engines propel aircraft, rockets, and put spacecraft into orbit. Depending on the purpose, they have a different device. But each of them has a supply of fuel, a chamber for its combustion and a nozzle that accelerates the jet stream.
The interplanetary automatic stations are also equipped with an instrument compartment and cabins with a life support system for astronauts.
Modern space rockets are complex, multi-stage aircraft that use the latest achievements in engineering. After launch, the fuel in the lower stage burns first, after which it separates from the rocket, reducing its total mass and increasing its speed.
Then the fuel is consumed in the second stage, and so on. Finally, the aircraft is brought to a given trajectory and begins its independent flight.
Let's dream a little
The great dreamer and scientist K. E. Tsiolkovsky gave future generations the confidence that jet engines will allow humanity to break out of the earth's atmosphere and rush into space. His prediction came true. The moon, and even distant comets, are successfully explored by spacecraft. 
In astronautics, liquid propellant engines are used. Using petroleum products as fuel, but the speeds that can be obtained with their help are insufficient for very long flights.
Perhaps you, our dear readers, will witness the flights of earthlings to other galaxies on vehicles with nuclear, thermonuclear or ion jet engines.
If this message was useful to you, I would be glad to see you
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 interaction forces 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 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 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 AD, China invented jet propulsion that 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 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. 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. Most different means science fiction writers, scientists, dreamers offered to achieve this goal. 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 apparatus 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 our shoulder feels, 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 speed of the exhaust gases of 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 formula of Tsiolkovsky for determining the speed of a space rocket is that in an airless space the rocket will develop the greater the speed, the greater the speed of the outflow of gases and the more number Tsiolkovsky.
"Physical foundations of the jet engine"
At the heart of modern powerful jet engines of various types is 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 dynamic 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.................
