Jet propulsion in technology. Jet engines
Questions.
1. Based on the law of conservation of momentum, explain why a balloon moves in the opposite direction to the stream of compressed air coming out of it.
2. Give examples of the reactive motion of bodies.
In nature, an example is the reactive movement of plants: the ripened fruits of a crazy cucumber; and animals: squid, octopus, jellyfish, cuttlefish, etc. (animals move by throwing out the water they absorb). In technology, the simplest example of jet propulsion is segner wheel, more complex examples are: the movement of rockets (space, gunpowder, military), water vehicles with a jet engine (hydrocycles, boats, motor ships), air vehicles with an air-jet engine (jet airplanes).
3. What is the purpose of rockets?
Rockets are used in various fields of science and technology: in military affairs, scientific research, astronautics, sports and entertainment.
4. Using Figure 45, list the main parts of any space rocket.
Spacecraft, instrument compartment, oxidizer tank, fuel tank, pumps, combustion chamber, nozzle.
5. Describe the principle of operation of a rocket.
In accordance with the law of conservation of momentum, a rocket flies due to the fact that gases with a certain momentum are pushed out of it at high speed, and the rocket is given an impulse of the same magnitude, but directed in the opposite direction. Gases are ejected through a nozzle in which the fuel burns, reaching high temperatures and pressures. The nozzle receives fuel and oxidizer, which are forced there by pumps.
6. What does the speed of a rocket depend on?
The speed of the rocket depends primarily on the speed of gas flow and the mass of the rocket. The rate of gas flow depends on the type of fuel and the type of oxidizer. The mass of the rocket depends, for example, on what speed they want to impart to it or on how far it should fly.
7. What is the advantage of multi-stage rockets over single-stage ones?
Multistage rockets are capable of reaching higher speeds and flying further than single-stage rockets.
8. How is a spacecraft landed?
The landing of the spacecraft is carried out in such a way that its speed decreases as it approaches the surface. This is achieved by using a braking system, which can be either a parachute braking system or braking can be carried out using a rocket engine, while the nozzle is directed downward (towards the Earth, the Moon, etc.), due to which the speed is reduced.
Exercises.
1. From a boat moving at a speed of 2 m/s, a person throws an oar with a mass of 5 kg at a horizontal speed of 8 m/s opposite to the movement of the boat. At what speed did the boat begin to move after the throw, if its mass together with the mass of the person is 200 kg?
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2. What speed will the rocket model get if the mass of its shell is 300 g, the mass of gunpowder in it is 100 g, and gases escape from the nozzle at a speed of 100 m/s? (Consider the gas outflow from the nozzle to be instantaneous).
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3. On what equipment and how is the experiment shown in Figure 47 carried out? What physical phenomenon is being demonstrated in this case, what does it consist of, and what physical law underlies this phenomenon?
Note: the rubber tube was positioned vertically until water began to flow through it.
A funnel with a rubber tube attached to it from below with a curved nozzle at the end was attached to the tripod using a holder, and a tray was placed below. Then they began to pour water from the container from above into the funnel, while the water poured from the tube into the tray, and the tube itself shifted from a vertical position. This experiment illustrates reactive motion based on the law of conservation of momentum.
4. Perform the experiment shown in Figure 47. When the rubber tube deviates from the vertical as much as possible, stop pouring water into the funnel. While the water remaining in the tube flows out, observe how it changes: a) the flight distance of the water in the stream (relative to the hole in the glass tube); b) position of the rubber tube. Explain both changes.
a) the flight range of water in the stream will decrease; b) as water flows out, the tube will approach a horizontal position. These phenomena are due to the fact that the water pressure in the tube will decrease, and therefore the impulse with which the water is ejected.
Reactivity and movement through this is a fairly widespread phenomenon in nature. Well, scientists and inventors “spied” it and used it in their technical developments. Examples of jet propulsion can be seen everywhere. Often we ourselves do not pay attention to the fact that this or that object - a living being, a technical mechanism - moves with the help of this phenomenon.
What is jet propulsion?
In living nature, reactivity is a movement that can occur in the event of separation of any particle from the body at a certain speed. In technology, a jet engine uses the same principle - the law of conservation of impulses. Examples of jet propulsion of technology: in a rocket consisting of a shell (which also includes an engine, control devices, a useful area for moving cargo) and fuel with an oxidizer, the fuel burns, turning into gases that burst out through the nozzles in a powerful jet, giving the entire structure speed in the opposite direction.
Examples of jet propulsion in nature
Quite a few living creatures use this principle of movement. It is characteristic of the larvae of some species of dragonflies, jellyfish, mollusks - scallops, cuttlefish, octopuses, squids. And in the plant world - the flora of the Earth - there are also species that use this phenomenon for insemination.
"Squirting cucumber"
Flora provides us with examples of jet propulsion. Only in appearance this plant with a strange nickname is similar to the cucumbers we are used to. And it acquired the epithet “mad” because of the unusual way of spreading its seeds. When ripe, the fruits of the plant bounce off the stalks. This creates a hole through which the cucumber shoots a liquid containing seeds suitable for propagation using reactivity. And the fruit itself can fly up to 12 meters in the direction opposite to the shot.
How does a cuttlefish move?
Examples of jet propulsion are quite widely represented in the fauna. The cuttlefish is a cephalopod with a special funnel located in the front part of the body. Through it (and through an additional side slit) water enters the animal’s body, into the gill cavity. Then the liquid is sharply thrown out through a funnel, and the cuttlefish can direct a special tube to the side or back. The resulting reverse force provides movement in different directions. 
Salpa
These animals from the tunicate family are striking examples of jet propulsion in nature. They have translucent cylindrical bodies of small size and live in the surface waters of the world's oceans. When moving, the animal draws in water through a hole located in the front of the body. The liquid is placed in a wide cavity of its body, in which the gills are located diagonally. The salpa takes a sip of water, and at the same time the hole closes tightly, and the muscles of the body - transverse and longitudinal - contract. As a result, the entire body of the salpa contracts, and the water is sharply pushed out of the rear hole. Thus, salps use the principle of reactivity in their movement in the water element. 
Jellyfish, mollusks, plankton
There are still inhabitants in the sea that move in a similar way. Everyone has probably seen various types of jellyfish in the water at least once while relaxing on the coast. But they also move using reactivity. Marine plankton, more precisely, some of its species, mollusks and scallops - they all move this way.
Examples of jet motion of bodies. Squid
The squid has a unique body structure. In fact, its structure contains a powerful jet engine with excellent efficiency. This representative of the fauna of the seas and oceans sometimes lives at great depths and reaches enormous sizes. Even the animal’s body resembles a rocket in its shape. More precisely, this modern rocket invented by scientists imitates the forms of squid created by nature. Moreover, for leisurely movements in the aquatic environment, a fin is used, but if a jerk is needed, then the principle of reactivity! 
If you are asked to give examples of jet propulsion in nature, then first of all we can talk about this mollusk. Its muscular mantle surrounds a cavity located in the body. Water is sucked in from the outside and then thrown out quite sharply through a narrow nozzle (reminiscent of a rocket). Result: the squid moves jerkily in the opposite direction. This feature allows the animal to move at fairly high speeds, overtaking its prey or escaping from pursuit. It can reach speeds comparable to a well-equipped modern vessel: up to 70 kilometers per hour. And some scientists who study the phenomenon in detail talk about speeds reaching 150 km/h! In addition, this representative of the ocean has good maneuverability due to the tentacles, folded in a bunch, bending when moving in the right directions.
This turntable can be called the world's first steam jet turbine.
Chinese rocket
Even earlier, many years before Heron of Alexandria, China also invented jet engine a slightly different device, now called fireworks rocket. Fireworks rockets should not be confused with their namesakes - signal rockets, which are used in the army and navy, and are also launched on national holidays under the roar of artillery fireworks. Flares are simply bullets compressed from a substance that burns with a colored flame. They are fired from large-caliber pistols - rocket launchers.
Flares are bullets compressed from a substance that burns with a colored flame. Chinese rocket It is a cardboard or metal tube, closed at one end and filled with a powder composition. When this mixture is ignited, a stream of gases escaping at high speed from the open end of the tube causes the rocket to fly in the direction opposite to the direction of the gas stream. Such a rocket can take off without the help of a rocket launcher. A stick tied to the rocket body makes its flight more stable and straight.
Fireworks using Chinese rockets Sea inhabitants
In the animal world:
Jet propulsion is also found here. Cuttlefish, octopuses and some other cephalopods have neither fins nor a powerful tail, but swim no worse than others sea inhabitants. These soft-bodied creatures have a fairly capacious sac or cavity in their body. Water is drawn into the cavity, and then the animal pushes this water out with great force. The reaction of the ejected water causes the animal to swim in the direction opposite to the direction of the stream.
The octopus is a sea creature that uses jet propulsion Falling cat
But the most interesting way of movement was demonstrated by the ordinary cat.
About a hundred and fifty years ago, a famous French physicist Marcel Depres stated:
But you know, Newton's laws are not entirely true. The body can move with the help of internal forces, without relying on anything or pushing away from anything.
Where is the evidence, where are the examples? - the listeners protested.
Want proof? If you please. A cat accidentally falling off a roof is proof! No matter how the cat falls, even head down, it will definitely stand on the ground with all four paws. But a falling cat does not rely on anything and does not push away from anything, but turns over quickly and deftly. (Air resistance can be neglected - it is too insignificant.)
Indeed, everyone knows this: cats, falling; always manage to get back on their feet.
Cats do this instinctively, but humans can do the same consciously. Swimmers who jump from a platform into the water know how to perform a complex figure - a triple somersault, that is, turn over three times in the air, and then suddenly straighten up, stop the rotation of their body and dive into the water in a straight line.
The same movements, without interaction with any foreign object, can be observed in the circus during the performance of acrobats - aerial gymnasts.
Performance of acrobats - aerial gymnasts The falling cat was photographed with a film camera and then on the screen they examined, frame by frame, what the cat does when it flies in the air. It turned out that the cat was quickly twirling its paw. The rotation of the paw causes a response movement of the entire body, and it turns in the direction opposite to the movement of the paw. Everything happens in strict accordance with Newton's laws, and it is thanks to them that the cat gets on its feet.
The same thing happens in all cases where a living creature, without any apparent reason, changes its movement in the air.
Jet boat
The inventors had an idea, why not adopt their swimming method from cuttlefish. They decided to build a self-propelled ship with jet engine. The idea is definitely feasible. True, there was no confidence in success: the inventors doubted whether such a thing would turn out jet boat better than a regular screw. It was necessary to do an experiment.
Jet boat - self-propelled vessel with a jet engine They selected an old tug steamer, repaired its hull, removed the propellers, and installed a water jet pump in the engine room. This pump pumped sea water and through a pipe pushed it behind the stern with a strong jet. The steamer floated, but it still moved slower than the screw steamer. And this is explained simply: an ordinary propeller rotates behind the stern, unconstrained, with only water around it; The water in the water-jet pump was driven by almost exactly the same screw, but it no longer rotated on the water, but in a tight pipe. Friction of the water jet against the walls occurred. Friction weakened the pressure of the jet. A steamship with a water-jet propulsion sailed slower than a screw-propelled one and consumed more fuel.
However, they did not abandon the construction of such steamers: they had important advantages. A boat equipped with a propeller must sit deep in the water, otherwise the propeller will uselessly foam the water or spin in the air. Therefore, screw steamers are afraid of shallows and riffles; they cannot sail in shallow water. And water-jet steamers can be built shallow-draft and flat-bottomed: they don’t need depth - where the boat goes, the water-jet steamer will go.
The first water-jet boats in the Soviet Union were built in 1953 at the Krasnoyarsk shipyard. They are designed for small rivers where ordinary steamboats cannot navigate.
Engineers, inventors and scientists began to study jet propulsion especially diligently when firearms. The first guns - all kinds of pistols, muskets and self-propelled guns - hit a person hard in the shoulder with each shot. After several dozen shots, the shoulder began to hurt so much that the soldier could no longer aim. The first cannons - squeaks, unicorns, culverins and bombards - jumped back when fired, so that it happened that the gunners-artillerymen were crippled if they did not have time to dodge and jump to the side.
The recoil of the gun interfered with accurate shooting, because the gun flinched before the cannonball or grenade left the barrel. This threw off the lead. The shooting turned out to be aimless.
Shooting with firearms Ordnance engineers began combating recoil more than four hundred and fifty years ago. First, the carriage was equipped with a coulter, which crashed into the ground and served as a strong support for the gun. Then they thought that if the gun was properly supported from behind, so that there was nowhere for it to roll away, then the recoil would disappear. But it was a mistake. The law of conservation of momentum was not taken into account. The guns broke all the supports, and the carriages became so loose that the gun became unsuitable for combat work. Then the inventors realized that the laws of motion, like any laws of nature, cannot be remade in their own way, they can only be “outwitted” with the help of science - mechanics.
They left a relatively small opener at the carriage for support, and placed the cannon barrel on a “sled” so that only one barrel rolled away, and not the entire gun. The barrel was connected to a compressor piston, which moves in its cylinder in the same way as a steam engine piston. But in the cylinder of a steam engine there is steam, and in a gun compressor there is oil and a spring (or compressed air).
When the gun barrel rolls back, the piston compresses the spring. At this time, the oil is forced through small holes in the piston on the other side of the piston. Strong friction occurs, which partially absorbs the movement of the rolling barrel, making it slower and smoother. Then the compressed spring straightens and returns the piston, and with it the gun barrel, to its original place. The oil presses on the valve, opens it and flows freely back under the piston. During rapid fire, the gun barrel moves almost continuously back and forth.
In a gun compressor, recoil is absorbed by friction.
Muzzle brake
When the power and range of the guns increased, the compressor was not enough to neutralize the recoil. It was invented to help him muzzle brake.
The muzzle brake is just a short steel pipe mounted on the end of the barrel and serves as its continuation. Its diameter is larger than the diameter of the barrel, and therefore it does not in any way interfere with the projectile flying out of the barrel. Several oblong holes are cut around the circumference of the tube walls.
Muzzle brake - reduces firearm recoil Powder gases flying out of the gun barrel following the projectile immediately diverge to the sides, and some of them fall into the holes of the muzzle brake. These gases hit the walls of the holes with great force, are repelled from them and fly out, but not forward, but slightly askew and backward. At the same time, they press forward on the walls and push them, and with them the entire barrel of the gun. They help the fire monitor because they tend to cause the barrel to roll forward. And while they were in the barrel, they pushed the gun back. The muzzle brake significantly reduces and dampens recoil.
Other inventors took a different path. Instead of fighting reactive movement of the barrel and try to extinguish it, they decided to use the gun's rollback to good effect. These inventors created many types of automatic weapons: rifles, pistols, machine guns and cannons, in which the recoil serves to eject the spent cartridge case and reload the weapon.
Rocket artillery
You don’t have to fight recoil at all, but use it: after all, action and reaction (recoil) are equivalent, equal in rights, equal in magnitude, so let reactive action of powder gases, instead of pushing the gun barrel back, sends the projectile forward towards the target. This is how it was created rocket artillery. In it, a jet of gases hits not forward, but backward, creating a forward-directed reaction in the projectile.
For rocket gun the expensive and heavy barrel turns out to be unnecessary. A cheaper, simple iron pipe works perfectly to direct the flight of the projectile. You can do without a pipe at all, and make the projectile slide along two metal slats.
In its design, a rocket projectile is similar to a fireworks rocket, it is only larger in size. In its head part, instead of a composition for a colored sparkler, an explosive charge of great destructive power is placed. The middle of the projectile is filled with gunpowder, which, when burned, creates a powerful stream of hot gases that pushes the projectile forward. In this case, the combustion of gunpowder can last a significant part of the flight time, and not just the short period of time while an ordinary projectile advances in the barrel of an ordinary gun. The shot is not accompanied by such a loud sound.
Rocket artillery is no younger than ordinary artillery, and perhaps even older: ancient Chinese and Arabic books written more than a thousand years ago report on the combat use of rockets.
In descriptions of battles of later times, no, no, and there will be a mention of combat missiles. When British troops conquered India, Indian rocket warriors, with their fire-tailed arrows, terrified the British invaders who enslaved their homeland. For the British at that time, jet weapons were a novelty.
Rocket grenades invented by the general K. I. Konstantinov, the courageous defenders of Sevastopol in 1854-1855 repelled the attacks of the Anglo-French troops.
Rocket
The huge advantage over conventional artillery - there was no need to carry heavy guns - attracted the attention of military leaders to rocket artillery. But an equally major drawback prevented its improvement.
The fact is that the propelling charge, or, as they used to say, the force charge, could only be made from black powder. And black powder is dangerous to handle. It happened that during production missiles the propellant exploded and the workers died. Sometimes the rocket exploded upon launch, killing the gunners. Making and using such weapons was dangerous. That's why it hasn't become widespread.
The work that began successfully, however, did not lead to the construction of an interplanetary spacecraft. The German fascists prepared and unleashed a bloody world war.
Missile
The shortcomings in the production of rockets were eliminated by Soviet designers and inventors. During the Great Patriotic War they gave our army excellent rocket weapons. Guards mortars were built - "Katyusha" and RS ("eres") were invented - rockets.
Missile In terms of quality, Soviet rocket artillery surpassed all foreign models and caused enormous damage to enemies.
Defending the Motherland, the Soviet people were forced to put all the achievements of rocket technology into the service of defense.
In fascist states, many scientists and engineers, even before the war, were intensively developing projects for inhumane weapons of destruction and mass murder. This they considered the purpose of science.
Self-driving aircraft
During the war, Hitler's engineers built several hundred self-driving aircraft: V-1 projectiles and V-2 rockets. These were cigar-shaped shells, 14 meters long and 165 centimeters in diameter. The deadly cigar weighed 12 tons; of which 9 tons are fuel, 2 tons are casing and 1 ton are explosives. "V-2" flew at speeds of up to 5,500 kilometers per hour and could rise to a height of 170-180 kilometers.
These means of destruction did not differ in hit accuracy and were only suitable for firing at such large targets as large and densely populated cities. The German fascists produced the V-2 200-300 kilometers from London in the belief that the city was large - it would hit somewhere!
It is unlikely that Newton could have imagined that his witty experience and the laws of motion he discovered would form the basis of weapons created by bestial anger towards people, and entire blocks of London would turn into ruins and become the graves of people captured by the raid of the blind “FAU”.
Spaceship
For many centuries, people have cherished the dream of flying in interplanetary space, of visiting the Moon, mysterious Mars and cloudy Venus. Many science fiction novels, novellas and short stories have been written on this topic. Writers sent their heroes into the sky on trained swans, in hot air balloons, in cannon shells, or in some other incredible way. However, all these methods of flight were based on inventions that had no support in science. People only believed that they would someday be able to leave our planet, but did not know how they would be able to do this.
Wonderful scientist Konstantin Eduardovich Tsiolkovsky in 1903 for the first time gave the scientific basis to the idea of space travel. He proved that people can leave the globe and a rocket will serve as a vehicle for this, because a rocket is the only engine that does not need any external support for its movement. That's why rocket capable of flying in airless space.
Scientist Konstantin Eduardovich Tsiolkovsky proved that people can leave the globe on a rocket In terms of its structure, the spacecraft should be similar to a rocket, only in its head there will be a cabin for passengers and instruments, and the rest of the space will be occupied by a supply of combustible mixture and an engine.
To give the ship the required speed, the right fuel is required. Gunpowder and other explosives are by no means suitable: they are both dangerous and burn too quickly, not providing long-term movement. K. E. Tsiolkovsky recommended using liquid fuel: alcohol, gasoline or liquefied hydrogen, burning in a stream of pure oxygen or some other oxidizing agent. Everyone recognized the correctness of this advice, because they did not know the best fuel at that time.
The first rocket with liquid fuel, weighing sixteen kilograms, was tested in Germany on April 10, 1929. The experimental rocket took off into the air and disappeared from view before the inventor and everyone present were able to trace where it flew. It was not possible to find the rocket after the experiment. The next time, the inventor decided to “outsmart” the rocket and tied a rope four kilometers long to it. The rocket took off, dragging its rope tail behind it. She pulled out two kilometers of rope, broke it and followed her predecessor in an unknown direction. And this fugitive also could not be found.
