In aviation and space medicine, overload is considered to be an indicator of the magnitude of the acceleration that a person experiences while moving. It represents the ratio of the resultant of the displacement forces to the mass of the human body.

Overload is measured in multiples of body weight in terrestrial conditions. For a person on the earth's surface, the overload is equal to unity. The human body is adapted to it, therefore it is invisible to people.

If an external force imparts an acceleration of 5 g to any body, then the overload will be 5. This means that the body weight under these conditions has increased five times compared to the initial one.

During takeoff of a conventional airliner, passengers in the cabin experience an overload of 1.5 g. According to international standards, the maximum allowable overload value for civil aircraft is 2.5 g.

At the moment of opening the parachute, a person is exposed to the action of inertial forces, causing an overload of up to 4 g. In this case, the overload indicator depends on the airspeed. For military parachutists, it can range from 4.3 g at a speed of 195 kilometers per hour to 6.8 g at a speed of 275 kilometers per hour.

The response to overloads depends on their magnitude, the rate of increase and the initial state of the organism. Therefore, both minor functional changes (a feeling of heaviness in the body, difficulty in movement, etc.) and very serious conditions can occur. These include complete loss of vision, dysfunction of the cardiovascular, respiratory and nervous systems, as well as loss of consciousness and the occurrence of pronounced morphological changes in tissues.

In order to increase the resistance of the pilot's body to accelerations in flight, anti-g-load and altitude-compensating suits are used, which, when overload, create pressure on the abdominal wall and lower extremities, which leads to a delay in the outflow of blood to the lower half of the body and improves blood supply to the brain.

To increase resistance to acceleration, centrifuge training, hardening of the body, oxygen breathing under high pressure are carried out.

During ejection, rough landing of an aircraft or landing on a parachute, significant overloads occur, which can also cause organic changes in the internal organs and the spine. To increase resistance to them, special chairs are used that have in-depth headrests, and that fix the body with belts, limb displacement limiters.

Overload is also the manifestation of gravity on board a spacecraft. If in terrestrial conditions the characteristic of gravity is the acceleration of gravity of bodies, then on board the spacecraft, the acceleration of gravity, which is equal in magnitude to the reactive acceleration in the opposite direction, is also among the characteristics of the overload. The ratio of this value to the value is called the "overload factor" or "overload".

In the acceleration section of the launch vehicle, the overload is determined by the resultant of non-gravitational forces - the thrust force and the aerodynamic drag force, which consists of the drag force directed opposite to the velocity and the lift force perpendicular to it. This resultant creates a non-gravitational acceleration that determines the overload.

Its coefficient in the acceleration section is several units.

If a space rocket under Earth conditions moves with acceleration under the action of engines or experiencing resistance from the environment, then there will be an increase in the pressure on the support, which will cause an overload. If the movement takes place with the engines turned off in the void, then the pressure on the support will disappear and a state of weightlessness will come.

At the launch of the spacecraft to the cosmonaut, the magnitude of which varies from 1 to 7 g. According to statistics, astronauts rarely experience overloads exceeding 4 g.

The ability to withstand overload depends on the ambient temperature, the oxygen content in the inhaled air, the duration of the astronaut's stay in zero gravity before acceleration, etc. There are other more complex or less perceptible factors, the influence of which has not yet been fully elucidated.

Under the influence of acceleration exceeding 1 g, the astronaut may develop visual impairments. Acceleration of 3 g in the vertical direction for more than three seconds can cause severe peripheral visual impairment. Therefore, in the compartments of the spacecraft, it is necessary to increase the level of illumination.

With longitudinal acceleration, the astronaut develops visual illusions. It seems to him that the object he is looking at is displaced in the direction of the resulting vector of acceleration and gravity. With angular accelerations, an apparent displacement of the object of sight occurs in the plane of rotation. This illusion is called peri-gross illusion and is a consequence of the effect of overload on the organs of the inner ear.

Numerous experimental studies, which were started by the scientist Konstantin Tsiolkovsky, have shown that the physiological effect of overload depends not only on its duration, but also on the position of the body. When a person is upright, a significant part of the blood is displaced into the lower half of the body, which leads to a violation of the blood supply to the brain. Due to the increase in their weight, the internal organs move downward and cause a strong tension in the ligaments.

To weaken the effect of high accelerations, the astronaut is placed in the spacecraft in such a way that the G-forces are directed along the horizontal axis, from the back to the chest. This position provides an efficient blood supply to the astronaut's brain at accelerations up to 10 g, and for a short time even up to 25 g.

When the spacecraft returns to Earth, when it enters the dense layers of the atmosphere, the astronaut experiences deceleration overloads, that is, negative acceleration. In terms of the integral value, the braking corresponds to the acceleration at the start.

The spacecraft entering the dense layers of the atmosphere is oriented so that the deceleration overloads have a horizontal direction. Thus, their impact on the astronaut is minimized, just like during the launch of the spacecraft.

The material was prepared on the basis of information from RIA Novosti and open sources

To increase resistance to acceleration, centrifuge training, hardening of the body, oxygen breathing under high pressure are carried out.

Its coefficient in the acceleration section is several units.

At the launch of the spacecraft to the cosmonaut, the magnitude of which varies from 1 to 7 g. According to statistics, astronauts rarely experience overloads exceeding 4 g.

The material was prepared on the basis of information from RIA Novosti and open sources

In this article, a physics and math tutor talks about how to calculate the overload that a body experiences when accelerating or decelerating. This material is very poorly considered at school, so students very often do not know how to carry out overload calculation, and after all, the corresponding tasks are found on the exam and the exam in physics. So read this article to the end or watch the accompanying video tutorial. The knowledge you gain will help you on the exam.

Let's start with the definitions. Overload called the ratio of the weight of a body to the magnitude of the force of gravity acting on this body at the surface of the earth. Body weight- This is the force that acts from the side of the body on a support or suspension. Pay attention, weight is exactly strength! Therefore, weight is measured in newtons, and not in kilograms, as some believe.

Thus, overload is a dimensionless quantity (newtons are divided by newtons, as a result, nothing is left). However, sometimes this value is expressed in the acceleration of gravity. For example, they say that the overload is equal, meaning that the weight of the body is twice the force of gravity.

Overload calculation examples

Let's show how to calculate the overload using specific examples. Let's start with the simplest examples and move on to more complex ones.

It is obvious that a person standing on the ground does not experience any overload. Therefore, I would like to say that its overload is zero. But let's not jump to conclusions. Let's draw the forces acting on this person:

Two forces are applied to a person: the force of gravity, which attracts the body to the ground, and the reaction force opposing it from the side of the earth's surface, directed upward. In fact, to be precise, this force is applied to the soles of a person's feet. But in this particular case, it does not matter, so it can be postponed from anywhere on the body. In the figure, it is plotted from the center of mass of a person.

The weight of a person is applied to the support (to the surface of the earth), in response, in accordance with Newton's third law, an equal in magnitude and oppositely directed force acts on the person from the support. So, to find the body weight, we need to find the value of the support reaction force.

Since a person stands still and does not fall through the ground, the forces that act on him are compensated. That is, and, accordingly,. That is, calculating the overload in this case gives the following result:

Remember this! In the absence of overloads, the overload is 1, not 0. As strange as it sounds.

Let us now determine what the overload of a person who is in free fall is equal to.

If a person is in a state of free fall, then only gravity acts on him, which is not balanced by anything. There is no support reaction force, just as there is no body weight. A person is in the so-called state of weightlessness. In this case, the overload is 0.

The astronauts are in a horizontal position in the rocket during its launch. This is the only way they can withstand the overload they experience without losing consciousness. Let's depict this in the figure:

In this state, two forces act on them: the reaction force of the support and the force of gravity. As in the previous example, the modulus of the astronauts' weight is equal to the value of the support reaction force:. The difference will be that the reaction force of the support is no longer equal to the force of gravity, as last time, since the rocket is moving upward with acceleration. Astronauts are also accelerated with the same acceleration synchronously with the rocket.

Then, in accordance with Newton's 2nd law in projection onto the Y-axis (see figure), we get the following expression:, whence. That is, the required overload is:

I must say that this is not the greatest overload that cosmonauts have to experience during the launch of a rocket. The overload can be up to 7. Prolonged exposure to such overloads on the human body inevitably leads to death.

At the bottom point of the "dead loop", two forces will act on the pilot: downward - force, upward toward the center of the "dead loop" - force (from the side of the seat in which the pilot sits):

The pilot's centripetal acceleration will also be directed there, where km / h m / s is the aircraft speed, is the radius of the "loop". Then again, in accordance with Newton's second law, in projection onto an axis directed vertically upward, we obtain the following equation:

Then the weight is ... So, calculating the overload gives the following result:

A very significant overload. The only thing that saves the pilot's life is that it does not last very long.

And finally, let's calculate the overload experienced by the driver of the car during acceleration.

So, the final speed of the car is equal to km / h m / s. If the car accelerates to this speed from rest in c, then its acceleration is equal to m / s 2. The car moves horizontally, therefore, the vertical component of the support reaction force is balanced by gravity, that is. In the horizontal direction, the driver accelerates with the vehicle. Consequently, according to Newton's 2-law, in projection onto an axis co-directed with acceleration, the horizontal component of the support reaction force is equal to.

The value of the total reaction force of the support is found by the Pythagorean theorem: ... It will be equal to the modulus of the weight. That is, the required overload will be equal to:

Today we have learned how to calculate congestion. Remember this material, it can be useful when solving tasks from the exam or OGE in physics, as well as in various entrance exams and olympiads.

Prepared by Sergey Valerievich

The force applied to the body, in SI units, is measured in newtons (1 N = 1 kg m / s 2). In technical disciplines, the kilogram-force is traditionally used as a unit of measure of force (1 kgf, 1 kg) and similar units: gram-force (1 rs, 1 G), ton-force (1 mf, 1 T). 1 kilogram-force is defined as the force imparting to a body of mass 1 kg normal acceleration equal by definition to 9.80665 m / s 2(this acceleration is approximately equal to the acceleration of gravity). Thus, according to Newton's second law, 1 kgf = 1 kg 9.80665 m / s 2 = 9,80665 N... We can also say that a body of mass 1 kg resting on the support has weight 1 kgf Often, for the sake of brevity, kilogram-force is simply called “kilogram” (and ton-force, respectively, “ton”), which sometimes gives rise to confusion among people who are not used to using different units.

Russian rocketry terminology traditionally uses “kilograms” and “tons” (more precisely, kilogram-force and ton-force) as the units of thrust for rocket engines. Thus, when they talk about a rocket engine with a thrust of 100 tons, they mean that this engine develops a thrust of 10 5 kg 9.80665 m / s 2$ \ approx $ 10 6 N.

A common mistake

Confusing newtons and kilogram-forces, some believe that a force of 1 kilogram-force imparts an acceleration of 1 to a body weighing 1 kilogram. m / s 2, that is, they write the erroneous "equality" 1 kgf / 1 kg = 1 m / s 2... At the same time, it is obvious that in fact 1 kgf / 1 kg = 9,80665 N / 1 kg = 9,80665 m / s 2- thus, an error of almost 10 times is allowed.

Example

<…>Accordingly, the force that presses on the particles within the weighted average radius will be equal to: 0.74 Gs / mm 2 · 0.00024 = 0.00018 Gs / mm 2 or 0.18 mG / mm 2. Accordingly, a force of 0.0018 mG will press on a middle particle with a cross section of 0.01 mm 2.
This force will give the particle an acceleration equal to its ratio to the mass of the average particle: 0.0018 mG / 0.0014 mG = 1.3 m / s 2. <…>

(Highlighting apollofacts.) Of course, a force of 0.0018 milligram-forces would impart an acceleration to a particle with a mass of 0.0014 milligrams almost 10 times more than what Mukhin counted: 0.0018 milligram-forces / 0.0014 milligrams = 0.0018 mg 9.81 m / s 2 / 0.0014 mg $ \ approx $ 13 m / s 2. (You can see that with the correction of this error alone, the depth of the crater calculated by Mukhin, which supposedly should have formed under the lunar module during landing, will immediately fall from 1.9 m required by Mukhin, up to 20 cm; however, the rest of the calculation is so absurd that this amendment cannot correct it).

Body weight

A-priory, body weight there is the force with which the body presses on the support or suspension. The weight of a body resting on a support or suspension (i.e., motionless relative to the Earth or other celestial body) is equal to

(1)

\ begin (align) \ mathbf (W) = m \ cdot \ mathbf (g), \ end (align)

where $ \ mathbf (W) $ is the weight of the body, $ m $ is the mass of the body, $ \ mathbf (g) $ is the acceleration of gravity at a given point. At the Earth's surface, acceleration due to gravity is close to normal acceleration (often rounded to 9.81 m / s 2). Body mass 1 kg has a weight of $ \ approx $ 1 kg 9.81 m / s 2$ \ approx $ 1 kgf... On the surface of the Moon, the acceleration of gravity is about 6 times less than on the surface of the Earth (more precisely, close to 1.62 m / s 2). Thus, on the Moon, bodies are about 6 times lighter than on Earth.

A common mistake

Body weight and mass are confused. The mass of the body does not depend on the celestial body, it is constant (if we neglect the relativistic effects) and is always equal to the same value - both on the Earth and on the Moon, and in zero gravity

Example

In the newspaper Duel, No. 20, 2002, the author describes the suffering that astronauts of the lunar module must experience when landing on the moon, and insists on the impossibility of such a landing:

Cosmonauts<…>are experiencing prolonged overload, the maximum value of which is 5. The overload is directed along the spine (the most dangerous overload). Ask military pilots if you can stay on the plane for 8 minutes. with a five-fold overload and even manage it. Imagine that after three days of being in the water (three days of flying to the Moon in zero gravity) you got out on land, you were placed in the Lunar cabin, and your weight became 400 kg (overload 5), your overalls were 140 kg, and your backpack behind the back - 250 kg. To prevent you from falling, you are held with a rope attached to the belt for 8 minutes, and then another 1.5 minutes. (no chairs, no lodgements). Do not bend your legs, lean on the armrests (hands should be on the controls). Has the blood drained from the head? Eyes hardly see? Don't die or faint<…>
it’s really bad to make the astronauts control the landing in the “standing” position with a prolonged 5-fold overload - it is simply IMPOSSIBLE.

However, as already shown, at the beginning of the descent, the astronauts experienced an overload of $ \ approx $ 0.66 g - that is, noticeably less than their normal earth weight (and they did not have any backpack behind them - they were directly connected to the ship's life support system) ... Before landing, the thrust of the engine almost balanced the weight of the spacecraft on the Moon, so the associated acceleration is $ \ approx $ 1/6 g - thus, during the entire landing, they experienced less stress than when they were simply standing on the ground. In fact, one of the tasks of the described cable system was precisely to help the astronauts stay on their feet. in conditions of reduced weight.

We've all heard epic stories of people who survived a bullet in the head, survived a fall from the 10th floor, or wandered at sea for months. But it is enough to place a person anywhere in the known universe with the exception of a thin layer of space, extending a couple of miles above sea level on Earth, or under it, and the death of a person is inevitable. No matter how strong and elastic our body may seem in some situations, in the context of the cosmos as a whole, it is frighteningly fragile.

Many of the boundaries within which the average person is able to survive are well defined. An example is the well-known "rule of threes", which determines how long we can go without air, water and food (approximately three minutes, three days, and three weeks, respectively). Other limits are more controversial because people rarely check them (or don't check them at all). For example, how long can you stay awake before you die? How high can you climb before choking? How much acceleration can your body withstand before it rips apart?

Experiments over the course of decades have helped define the boundaries within which we live. Some of them were purposeful, some were random.

How long can we stay awake?

It is known that the Air Force pilots, after three or four days of wakefulness, fell into such an uncontrollable state that they crashed their planes (falling asleep at the helm). Even one night without sleep affects the driver's ability in the same way as drunkenness. The absolute limit for voluntary sleep resistance is 264 hours (about 11 days). That record was set by 17-year-old Randy Gardner for the 1965 High School Science Projects Fair. Before he fell asleep on the 11th day, he is, in fact, a plant with open eyes.

But after what time would he die?

In June this year, a 26-year-old Chinese man died after 11 days without sleep trying to watch all the games of the European Championship. At the same time, he consumed alcohol and smoked, which makes it difficult to accurately determine the cause of death. But just because of lack of sleep, most certainly not a single person died. And for obvious ethical reasons, scientists cannot determine this period in laboratory conditions.

But they were able to do it on rats. In 1999, sleep researchers at the University of Chicago placed rats on a spinning disc above a pool of water. They continuously recorded the behavior of the rats using a computer program capable of recognizing the onset of sleep. When the rat began to fall asleep, the disc suddenly turned, waking it up, throwing it against the wall and threatening to throw it into the water. Rats typically died after two weeks of this treatment. Before death, the rodents showed symptoms of hypermetabolism, a condition in which the body's metabolic rate at rest increases so much that all excess calories are burned, even when the body is completely immobile. Hypermetabolism is associated with a lack of sleep.

How much radiation can we withstand?

Radiation is a long-term hazard as it causes DNA mutations, changing the genetic code in a way that leads to cancerous cell growth. But what dose of radiation will kill you immediately? According to Peter Caracappa, a nuclear engineer and radiation safety specialist at Rensler Polytechnic Institute, a dose of 5-6 sieverts (Sv) in a matter of minutes will destroy too many cells for the body to cope with. "The longer the dose accumulation period, the higher the chances of survival, since the body is trying to heal itself at this time," explained Caracappa.

By comparison, some workers at Japan's Fukushima nuclear power plant received 0.4 to 1 Sv of radiation in an hour while confronting an accident last March. Although they survived, their risk of cancer is significantly increased, scientists say.

Even if nuclear power plant accidents and supernova explosions are avoided, the natural background radiation on Earth (from sources such as uranium in the soil, cosmic rays and medical devices) increases our chances of getting cancer by 0.025 percent any year, Caracappa says. This sets a somewhat strange limit to human life span.

"The average person ... receiving an average dose of background radiation each year for 4,000 years, in the absence of other factors, will inevitably get radiation-induced cancer," says Caracappa. In other words, even if we can defeat all diseases and turn off the genetic commands that control the aging process, we still won't live more than 4,000 years.

How much acceleration can we sustain?

The rib cage protects our heart from violent beats, but it is not a reliable protection against the jerking that technology has made possible today. What acceleration can this organ of ours withstand?

NASA and military researchers have conducted a series of tests in an attempt to answer this question. The purpose of these tests was the safety of structures of space and airborne vehicles. (We don't want the astronauts to faint when the rocket takes off.) Horizontal acceleration - a jerk to the side - has a negative effect on our insides, due to the asymmetry of the forces acting. According to a recent article in Popular Science, a horizontal acceleration of 14 g can tear our organs apart. Acceleration along the body towards the head can displace all the blood towards the legs. This vertical acceleration of 4 to 8 g will knock you unconscious. (1 g is the force of gravity that we feel on the earth's surface, at 14 g is the force of gravity on a planet 14 times more massive than ours.)

Forward or backward acceleration is most beneficial for the body, since the head and heart are accelerated in the same way. The military's 1940s and 1950s "human braking" experiments (which essentially used rocket sleds propelled across the entire Edwards Air Force Base in California) showed that we can brake at an acceleration of 45 g, and still be alive to talk about it. With such braking, traveling at speeds in excess of 1000 km per hour, you can stop in a split second, having traveled several hundred feet. When braking at 50 g, we are estimated by experts, we are likely to turn into a bag of individual organs.

What environmental changes are we able to withstand?

Different people are able to withstand various changes in the usual atmospheric conditions, regardless of whether it is a change in temperature, pressure, or the oxygen content of the air. Survival limits are also related to how slowly environmental changes occur, as our bodies are able to gradually adjust oxygen consumption, and alter metabolism in response to extreme conditions. But, nevertheless, we can roughly estimate what we are able to withstand.

Most people begin to suffer from overheating after 10 minutes in an extremely humid and hot environment (60 degrees Celsius). Determining the boundaries of death from chilling is more difficult. A person usually dies when their body temperature drops to 21 degrees Celsius. But how long it takes depends on how "accustomed to the cold" a person is, and whether the mysterious latent form of "hibernation", which, as you know, sometimes occurs, has manifested itself.

Survival boundaries are much better set for long-term comfort. According to a 1958 NASA report, humans can live indefinitely in environments with temperatures ranging from 4 to 35 degrees Celsius, provided that the latter is at or below 50 percent relative humidity. With lower humidity, the maximum temperature increases, as less moisture in the air makes it easier to sweat and thereby cool the body.

As you can tell from science fiction films in which the astronaut's helmet is opened outside the spacecraft, we cannot survive for long at very low pressure or oxygen levels. At normal atmospheric pressure, air contains 21 percent oxygen. We will die of suffocation if the oxygen concentration drops below 11 percent. Too much oxygen also kills, gradually causing pneumonia over several days.

We pass out when the pressure drops below 57 percent of atmospheric pressure, which equates to an ascent of 4500 meters. Climbers are able to climb higher mountains as their bodies gradually adapt to the decrease in oxygen, but no one can survive long enough without oxygen tanks at an altitude of over 7900 meters.

It is about 8 kilometers up. And to the border of the known universe is still almost 46 billion light years away.

Natalie Wolchover

Life's Little Mysteries

august 2012

Translation: Gusev Alexander Vladimirovich