In this article, a tutor in physics and mathematics talks about how to calculate the overload experienced by the body at the time of acceleration or deceleration. This material is very poorly considered at school, so students very often do not know how to implement overload calculation, but the corresponding tasks are found at the exam and the exam in physics. So read this article to the end or watch the attached video tutorial. The knowledge you gain will be useful to you on the exam.
Let's start with 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 is the force that acts from the side of the body on a support or suspension. Remember, weight is power! Therefore, weight is measured in newtons, and not in kilograms, as some believe.
Thus, overload is a dimensionless quantity (newtons are divided by newtons, nothing remains as a result). However, sometimes this quantity is expressed in free fall accelerations. They say, for example, that the overload is equal to, meaning that the weight of the body is twice the force of gravity.
Overload calculation examples
Let's show how to calculate the overload on specific examples. Let's start with the simplest examples and move on to more complex ones.
Obviously, a person standing on the ground does not experience any g-forces. Therefore, I want 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: gravity, which attracts the body to the earth, and reaction force, which opposes it from the earth's surface, directed upwards. 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 any point on the body. In the figure, it is laid off 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 3rd law, an equal and oppositely directed force acts on the person from the side of the support. So to find the weight of the body, we need to find the magnitude of the reaction force of the support.
Since a person stands still and does not fall through the ground, the forces that act on him are compensated. That is, and, respectively, . That is, the calculation of overload in this case gives the following result:
Remember this! In the absence of overloads, the overload is 1, not 0. Strange as it may sound.
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. Only in this way can they withstand the overload that 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 weight of the astronauts is equal to the magnitude of the reaction force of the support: . The difference will be that the reaction force of the support is no longer equal to the force of gravity, as it was last time, since the rocket is moving upwards with acceleration . With the same acceleration, cosmonauts accelerate synchronously with the rocket.
Then, in accordance with Newton's 2nd law in the projection onto the Y axis (see figure), we obtain the following expression: , whence . That is, the desired overload is equal to:
I must say that this is not the biggest overload that astronauts have to experience during a rocket launch. Overload can reach up to 7. Prolonged exposure to such overloads on the human body inevitably leads to death.
At the lower point of the "dead loop" two forces will act on the pilot: down - force , up, to the center of the "dead loop" - force (from the side of the seat in which the pilot sits):
The centripetal acceleration of the pilot will also be directed there, where km / h m / s is the speed of the aircraft, is the radius of the “dead loop”. Then again, in accordance with Newton's 2nd law in the projection on the axis directed vertically upwards, we obtain the following equation:
Then the weight is 
. So, the overload calculation 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, we calculate the overload that the driver of the car experiences during acceleration.
So, the final speed of the car is 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 car. Therefore, according to Newton's 2-law in the projection on the axis co-directed with the acceleration, the horizontal component of the support reaction force is equal to .
The value of the total reaction force of the support can be found by the Pythagorean theorem: 
. It will be equal to the modulus of weight. That is, the required overload will be equal to:
Today we learned how to calculate overload. Remember this material, it can be useful when solving tasks from the Unified State Exam or OGE in physics, as well as at various entrance exams and olympiads.
Prepared by Sergey Valerievich
Overload is the ratio of the resultant of all forces (except weight) acting on the aircraft to the weight of the aircraft.
Overloads are defined in the coupled coordinate system:
nx- longitudinal overload; nu- normal overload; nz- lateral overload.
Full overload is determined by the formula
Longitudinal overload nx occurs when the engine thrust and drag change.
If the thrust of the engine is greater than the drag, then the overload is positive. If the drag value is greater than the thrust force of the engine, then the overload is negative.
Longitudinal overload is determined by the formula
Lateral overload nz occurs during the flight of an aircraft with sliding. But the magnitude of the lateral aerodynamic force Z is very small. Therefore, in the calculations, the lateral overload is taken equal to zero. Lateral overload is determined by the formula
The performance of aerobatic maneuvers is mainly accompanied by the occurrence of large normal g-forces.
Normal overload nu called the ratio of the lift to the weight of the aircraft and is determined by the formula
Normal overload, as can be seen from formula (11.5), is created by a lifting force. In level flight with a calm atmosphere, the lift force is equal to the weight of the aircraft, therefore, the overload will be equal to one:
Rice. 6 The effect of the centrifugal force of inertia on the pilot a - with a sharp increase in the angle of attack, b - with a sharp decrease in the angle of attack
In curved flight, when the lift force becomes greater than the weight of the aircraft, the g-force will be greater than one.
When an aircraft moves along a curved path, the centripetal force is, as already mentioned, the lifting force, i.e., air pressure on the wings. With this value of the centripetal force, there is always an equal but opposite in direction centrifugal force of inertia, which is expressed by the pressure force of the wings on the air. Moreover, the centrifugal force acts like a weight (mass), and since it is always equal to the centripetal force, when the latter increases, it increases by the same amount. Thus, aerodynamic overload is similar to an increase in the weight of an aircraft (pilot).
When an overload occurs, it seems to the pilot that his body has become heavier.
Normal overload is divided into positive and negative. When an overload presses the pilot to the seat, then this overload positive if, however, he separates him from the seat and keeps him on the harness - negative (Fig. 6).
In the first case, the blood will drain from the head to the feet, in the second case, it will flow to the head.
As already mentioned, an increase in lift in curvilinear motion is equivalent to an increase in the weight of the aircraft by the same amount, then
(11.6)
(11.7)
where n ur - disposable overload.
From formula (11.7) it can be seen that the amount of available overload is determined by the reserve of lift coefficients (reserves of angles of attack) from that required for level flight to its safe value (Su TR or Su KR).
The maximum possible normal overload can be obtained when, in flight at a given speed and flight altitude, the aircraft's ability to create lift is fully utilized. This overload can be obtained in the case when the aircraft abruptly (without a noticeable decrease in flight speed) is brought to C y \u003d C y max:
(11.8)
However, it is undesirable to bring the aircraft to such an overload, as there will be a loss of stability and a stall into a spin or a spin. For this reason, at high flight speeds, especially when exiting a dive, it is not recommended to sharply deflect the control stick towards yourself. Therefore, the maximum possible or available overload is taken to be smaller in order to prevent the aircraft from entering the shaking mode. The formula for determining this overload is
(11.9)
For the Yak-52 and Yak-55 aircraft, the graphic dependences of the available overloads on the flight speed are shown in Fig. 7, Fig. 8. When performing flights on Yak-52 and Yak-55 aircraft, the available normal overload is mainly limited by the strength characteristics of the aircraft.
The maximum allowable operational overload for the Yak-52 aircraft:
with wheeled chassis:
positive +7;
negative -5;
with ski chassis:
positive +5;
negative -3.
The maximum allowable operational overload for the Yak-55 aircraft:
in training version:
positive +9;
negative -6;
in the distillation version:
positive +5;
negative -3.
Exceeding these overloads in flight is prohibited, since residual deformations in the aircraft structure may appear.
When performing steady curvilinear maneuvers, the overload depends on the thrust reserve of the power plant. The thrust reserve is determined from the condition of maintaining a given speed during the entire maneuver.
Limit overload for available thrust PREV called the greatest overload, at which the thrust of the power plant still balances the drag. It is determined by the formula
(11.10)
The limiting available thrust overload depends on the flight speed and altitude, since the above factors affect the available thrust Pp and the aerodynamic quality K on the speed.
For each speed value, the available thrust values are taken from the Pp (V) curve, the value of the coefficient Su is taken from the polar for the corresponding speed V, and calculated by formula (11.10).
When maneuvering in a horizontal plane with an overload less than available, but more than the limiting thrust, the aircraft will lose speed or flight altitude.
In aviation and space medicine, overload is considered to be an indicator of the magnitude of the acceleration that affects a person when he moves. It is the ratio of the resultant moving forces to the mass of the human body.
Overload is measured in units of multiples of body weight in terrestrial conditions. For a person on the earth's surface, the overload is equal to one. The human body is adapted to it, so it is invisible to people.
If an external force imparts an acceleration of 5 g to any body, then the overload will be equal to 5. This means that the weight of the body under these conditions has increased five times compared to the original.
During takeoff of a conventional airliner, passengers in the cabin experience an overload of 1.5 g. According to international standards, the maximum permissible value of overloads for civil aircraft is 2.5 g.
At the moment of opening the parachute, a person is subjected to the action of inertial forces, causing an overload that reaches 4 g. In this case, the overload indicator depends on the airspeed. For military paratroopers, 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 shifts (feeling of heaviness in the body, difficulty in movements, 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 body of pilots to accelerations in flight, anti-g and altitude-compensating suits are used, which, when overloaded, create pressure on the abdominal wall and lower limbs, 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 accelerations, training is carried out on a centrifuge, hardening of the body, breathing oxygen under high pressure.
During an ejection, a rough landing of an aircraft or a parachute landing, significant overloads occur, which can also cause organic changes in the internal organs and spine. To increase resistance to them, special chairs are used with deep headrests, and fixing the body with belts, limiters of displacement of the limbs.
Overloading is also a manifestation of gravity on board the spacecraft. If under terrestrial conditions the characteristic of gravity is the acceleration of free fall of bodies, then on board the spacecraft the overload characteristics also include the acceleration of free fall, which is equal in magnitude to the jet acceleration in the opposite direction. 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 speed and the lift force perpendicular to it. This resultant creates a non-gravitational acceleration, which determines the overload.
Its coefficient in the acceleration section is several units.
If a space rocket in Earth conditions moves with acceleration under the action of engines or experiencing environmental resistance, then there will be an increase in pressure on the support, which will cause an overload. If the movement occurs with the engines turned off in a void, then the pressure on the support will disappear and a state of weightlessness will come.
At the launch of the spacecraft on the astronaut, the value of which varies from 1 to 7 g. According to statistics, astronauts rarely experience g-forces exceeding 4 g.
The ability to endure overloads depends on the ambient temperature, the oxygen content in the inhaled air, the duration of the astronaut's stay in weightlessness before starting acceleration, etc. There are other more complex or less perceptible factors, the influence of which is not yet fully understood.
Under the action of an acceleration exceeding 1 g, the astronaut may experience visual impairment. Acceleration of 3 g in the vertical direction, which lasts more than three seconds, may cause serious impairment of peripheral vision. Therefore, it is necessary to increase the level of illumination in the compartments of the spacecraft.
With longitudinal acceleration, the astronaut has visual illusions. It seems to him that the object he is looking at is shifting in the direction of the resulting vector of acceleration and gravity. With angular accelerations, an apparent displacement of the object of vision in the plane of rotation occurs. This illusion is called circumgyral and is a consequence of the impact of overloads on the organs of the inner ear.
Numerous experimental studies, which were started by the scientist Konstantin Tsiolkovsky, showed that the physiological effect of overload depends not only on its duration, but also on the position of the body. When a person is in a vertical position, a significant part of the blood is shifted to the lower half of the body, which leads to disruption of the blood supply to the brain. Due to the increase in their weight, the internal organs are shifted downward and cause a strong tension in the ligaments.
To reduce 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 effective blood supply to the cosmonaut'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 integral value, deceleration corresponds to acceleration at start.
A spacecraft entering the dense layers of the atmosphere is oriented so that the deceleration g-forces have a horizontal direction. Thus, their impact on the astronaut is minimized, just as during the launch of the spacecraft.
The material was prepared on the basis of information from RIA Novosti and open sources
Aircraft. Overload is a dimensionless quantity, however, often the unit of overload is denoted in the same way as the acceleration of gravity, g. An overload of 1 unit (or 1g) means straight flight, 0 means free fall or weightlessness. If an aircraft turns at a constant altitude with a bank of 60 degrees, its structure experiences an overload of 2 units.
The permissible value of overloads for civil aircraft is 2.5. An ordinary person can withstand any overload up to 15G for about 3-5 seconds without shutting down, but a person can withstand large overloads from 20-30G or more without shutting down for no more than 1-2 seconds and depending on the size of the overload, for example 50G = 0.2 sec. Trained pilots in anti-g suits can tolerate g-forces from -3 ... -2 to +12. Resistance to negative, upward g-forces is much lower. Usually, at 7-8 G, the eyes “turn red” and the person loses consciousness due to a rush of blood to the head.
Overload is a vector quantity directed in the direction of speed change. For a living organism, this is essential. When overloaded, human organs tend to remain in the same state (uniform rectilinear motion or rest). With positive G-force (head-to-foot), blood flows from the head to the legs. The stomach goes down. When negative, the blood rises to the head. The stomach can turn out along with the contents. When another car crashes into a stationary car, the person sitting will experience back-chest overload. Such an overload is tolerated without much difficulty. Astronauts during takeoff endure the overload lying down. In this position, the vector is directed chest-back, which allows you to withstand several minutes. Cosmonauts do not use anti-G devices. They are a corset with inflatable hoses, inflated from the air system and hold the outer surface of the human body, slightly preventing the outflow of blood.
Notes
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See what "Overload (aviation)" is in other dictionaries:
G-force: G-force (aviation) lift-to-weight ratio G-force (technical) in accelerating objects G-force (chess) a chess situation where pieces (figure) are not able to cope with their tasks. Overload ... ... Wikipedia
1) P. at the center of mass is the ratio n of the resulting force R (the sum of thrust and aerodynamic force, see Aerodynamic forces and moments) to the product of the mass of the aircraft m and the acceleration of gravity g: n \u003d R / mg (when determining P. for ... … Encyclopedia of technology
The largest neymax and the smallest neymin allowable values of normal overload ny in terms of structural strength. The value of E. p. is determined on the basis of strength standards for various design cases, for example, for maneuver, flight during bumpy. By… … Encyclopedia of technology
We've all heard the epic stories of people surviving a bullet to the head, surviving a fall from a 10th floor, or roaming the sea for months. But it is enough to place a person anywhere in the known universe except for a thin layer of space extending a couple of miles above sea level on Earth, or below 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 can survive are fairly 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 test them (or don't test them at all). For example, how long can you stay awake before you die? How high can you get up before you suffocate? How much acceleration can your body withstand before it breaks apart?
Decades of experiments have helped define the boundaries within which we live. Some of them were purposeful, some were accidental.
How long can we stay awake?
It is known that 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 ability of the driver in the same way as intoxication. The absolute limit of voluntary sleep resistance is 264 hours (about 11 days). This record was set by 17-year-old Randy Gardner for a high school science project fair in 1965. Before he fell asleep on the 11th day, he was actually a plant with open eyes.
But how long would it take for him to die?
In June of this year, a 26-year-old Chinese man died after 11 days without sleep while trying to watch all the European Championship games. At the same time, he consumed alcohol and smoked, which makes it difficult to determine the exact cause of death. But just because of lack of sleep, definitely not a single person died. And for obvious ethical reasons, scientists cannot determine this period in the laboratory.
But they were able to do it on rats. In 1999, sleep researchers at the University of Chicago placed rats on a spinning disk above a pool of water. They continuously recorded the behavior of the rats using a computer program capable of recognizing the onset of sleep. As the rat began to fall asleep, the disc would suddenly turn, awakening it, throwing it against the wall and threatening to throw it into the water. The rats typically died after two weeks of this treatment. Before death, the rodents showed symptoms of hypermetabolism, a condition in which the resting metabolic rate of the body increases so much that all excess calories are burned, even when the body is completely immobile. Hypermetabolism is associated with lack of sleep.
How much radiation can we withstand?
Radiation is a long-term danger because 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 few minutes will destroy too many cells for the body to cope with. "The longer the dose accumulation period, the higher the chances of survival, as the body is trying to repair itself at this time," Caracappa explained.
By comparison, some workers at Japan's Fukushima nuclear power plant received 0.4 to 1 Sv of radiation in an hour while confronting the accident last March. Although they survived, their cancer risk is significantly increased, scientists say.
Even if nuclear accidents and supernova explosions are avoided, Earth's natural background radiation (from sources such as uranium in the soil, cosmic rays and medical devices) increases our chances of getting cancer in any given year by 0.025 percent, Caracappa says. This places a somewhat odd limit on human lifespan.
"The average person ... receiving an average dose of background radiation every year for 4,000 years, in the absence of other factors, will inevitably get cancer caused by radiation," Caracappa says. 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 beyond 4,000 years.
How much acceleration can we sustain?
The ribcage protects our heart from strong impacts, but it is not a reliable protection against jerks, which have become possible thanks to the development of technology today. What acceleration can this organ of ours withstand?
NASA and military researchers have run a series of tests in an attempt to answer this question. The purpose of these tests was the safety of structures of space and air vehicles. (We don't want astronauts to pass out when a rocket takes off.) Horizontal acceleration - a sideways jerk - has a negative effect on our insides, due to the asymmetry of the acting forces. According to a recent article published in the journal Popular Science, a horizontal acceleration of 14 g is capable of tearing our organs apart. Acceleration along the body towards the head can shift all the blood to the legs. Such a vertical acceleration of 4 to 8 g will make you unconscious. (1 g is the force of gravity that we feel on the earth's surface, at 14 g is this force of gravity on a planet 14 times more massive than ours.)
Acceleration directed forward or backward is the most favorable for the body, since in this case both the head and the heart are accelerated equally. Military "human braking" experiments in the 1940s and 1950s (essentially using rocket sleds moving all over Edwards Air Force Base in California) showed that we could brake at an acceleration of 45 g and still be alive to talk about it. With this kind of braking, moving at speeds above 1000 km per hour, you can stop in a split second, having traveled several hundred feet. When braking at 50 g, we are, according to experts, we are likely to turn into a bag of separate organs.
What environmental changes are we able to withstand?
Different people are able to withstand different changes in the usual atmospheric conditions, whether it be a change in temperature, pressure, or oxygen content in the air. Survival limits are also related to how slowly environmental changes occur, as our body is able to gradually adjust its oxygen intake and change 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 limits of death from freezing is more difficult. A person usually dies when their body temperature drops to 21 degrees Celsius. But how long this takes depends on how "accustomed to the cold" one is, and whether the mysterious, latent form of "hibernation" that is known to occasionally occur has emerged.
Survival boundaries are much better set for long-term comfort. According to a 1958 NASA report, humans can live indefinitely in an environment that is between 4 and 35 degrees Celsius, as long as the latter temperature is below 50 percent relative humidity. With less humidity, the maximum temperature increases, since less moisture in the air facilitates the process of sweating, and thereby cooling the body.
As you can tell from science fiction films in which an astronaut's helmet is opened outside of a spacecraft, we are not able to survive for long at very low levels of pressure or oxygen. At normal atmospheric pressure, air contains 21 percent oxygen. We will suffocate if the oxygen concentration drops below 11 percent. Too much oxygen also kills, gradually causing pneumonia over several days.
We lose consciousness when the pressure drops below 57 percent of atmospheric pressure, which corresponds to an ascent to a height of 4500 meters. Climbers are able to climb higher mountains as their bodies gradually adapt to the reduced oxygen supply, but no one can live long enough without oxygen tanks above 7,900 meters.
It's about 8 kilometers up. And there are still almost 46 billion light-years to the edge of the known universe.
Natalia Volchover (Natalie Wolchover)
"Little Mysteries of Life" (Life's Little Mysteries)
August 2012
Translation: Gusev Alexander Vladimirovich