For some special reason in the world great attention it is focused specifically on the speed of acceleration of the car from 0 to 100 km/h (in the USA from 0 to 60 mph). Experts, engineers, sports car enthusiasts, as well as ordinary car enthusiasts, with some kind of obsession, constantly monitor technical characteristics cars, which usually reveals the dynamics of car acceleration from 0 to 100 km/h. Moreover, all this interest is observed not only in sports cars for which the dynamics of acceleration from a standstill is very important, but also in completely ordinary economy class cars.
These days, most of the interest in acceleration dynamics is directed towards electric modern cars, which began to slowly displace sports supercars with their incredible acceleration speed from the auto niche. For example, just a few years ago it seemed simply fantastic that a car could accelerate to 100 km/h in just over 2 seconds. But today some modern ones have already come close to this indicator.
This naturally makes you wonder: What speed of acceleration of a car from 0 to 100 km/h is dangerous to human health? After all, the faster the car accelerates, the more load the driver who is (sitting) behind the wheel experiences.
Agree with us that the human body has its own certain limits and cannot withstand the endless increasing loads that act and exert on it during rapid acceleration vehicle, a certain impact. Let us find out together what the maximum acceleration of a car can theoretically and practically be withstood by a person.
Acceleration, as we all probably know, is a simple change in the speed of movement of a body per unit of time. The acceleration of any object on the ground depends, as a rule, on gravity. Gravity is a force acting on any material body that is close to the surface of the earth. The force of gravity on the surface of the earth consists of gravity and the centrifugal force of inertia, which arises due to the rotation of our planet.
If we want to be absolutely precise, then human overload of 1g sitting behind the wheel of a car is formed when the car accelerates from 0 to 100 km/h in 2.83254504 seconds.
And so, we know that when overloaded in 1g the person does not experience any problems. For example, a production Tesla Model S car (an expensive special version) can accelerate from 0 to 100 km/h in 2.5 seconds (according to the specification). Accordingly, the driver behind the wheel of this car will experience an overload of 1.13g.
This, as we see, is more than the overload that a person experiences in ordinary life and which arises due to gravity and also due to the movement of the planet in space. But this is quite a bit and the overload does not pose any danger to humans. But, if we get behind the wheel of a powerful dragster (sports car), then the picture here is completely different, since we are already seeing different overload figures.
For example, the fastest one can accelerate from 0 to 100 km/h in just 0.4 seconds. As a result, it turns out that this acceleration causes overload inside the car in 7.08g. This is already, as you see, a lot. Driving such a crazy vehicle you will not feel very comfortable, and all due to the fact that your weight will increase almost seven times compared to before. But despite this not very comfortable state with such acceleration dynamics, this (this) overload is not capable of killing you.
So how then does a car have to accelerate to kill a person (the driver)? In fact, it is impossible to answer this question unambiguously. The point here is the following. Each organism of any person is purely individual and it is natural that the consequences of exposure to certain forces on a person will also be completely different. Overload for some at 4-6g even for a few seconds it will already be (is) critical. Such an overload can lead to loss of consciousness and even death of that person. But usually such overload is not dangerous for many categories of people. There are known cases when overload in 100g allowed a person to survive. But the truth is, this is very rare.
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 associated coordinate system:
nx- longitudinal overload; nу- normal overload; nz- lateral overload.
Full overload is determined by the formula
Longitudinal overload nх occurs when engine thrust and drag change.
If the engine thrust is greater than the drag, then the overload is positive. If the magnitude of the drag is greater than the engine thrust, then the overload is negative.
Longitudinal overload is determined by the formula
Lateral overload nz occurs when the aircraft is flying in a sliding state. But in terms of magnitude, the lateral aerodynamic force Z is very small. Therefore, in 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 overloads.
Normal overload nу is called the ratio of 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 lifting force. In horizontal flight in a calm atmosphere, the lift force is equal to the weight of the aircraft, therefore, the overload will be equal to unity:
Rice. 6 The effect of centrifugal inertial force 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 overload will be greater than one.
When an airplane moves along a curved path, the centripetal force is, as already mentioned, lift, i.e., air pressure on the wings. In this case, the magnitude of the centripetal force is always accompanied by an equal, but opposite in direction, centrifugal force of inertia, which is expressed by the force of pressure of the wings on the air. Moreover, the centrifugal force acts like 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 the aircraft (pilot).
When overload occurs, the pilot feels as if his body has become heavier.
Normal overload is divided into positive and negative. When the overload presses the pilot into the seat, then this overload positive, if he separates him from the seat and holds him on the seat belts - negative (Fig. 6).
In the first case, the blood will flow 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 level - available overload.
From formula (11.7) it is clear that the amount of available overload is determined by the reserve of lift coefficients (margin of angles of attack) from those required for horizontal flight to its safe value (Su TR or Su CR).
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 is sharply (without a noticeable decrease in flight speed) brought to C y = 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 tailspin or spin rotation. For this reason, it is not recommended to sharply tilt the control stick toward you at high flight speeds, especially when exiting a dive. Therefore, the maximum possible or available overload is taken to be smaller in value in order to prevent the aircraft from entering the shaking mode. The formula for determining this overload has the form
(11.9)
For the Yak-52 and Yak-55 aircraft, graphical dependences of available overloads on 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.
Maximum permissible operational overload for the Yak-52 aircraft:
with wheeled chassis:
positive +7;
negative -5;
with ski chassis:
positive +5;
negative -3.
Maximum permissible operational overload for the Yak-55 aircraft:
in the training version:
positive +9;
negative -6;
in distillation version:
positive +5;
negative -3.
Exceeding these overloads in flight is prohibited, since residual deformations may appear in the aircraft structure.
When performing steady-state curved 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 throughout the entire maneuver.
Maximum overload for available thrust PR is 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 maximum overload for the available thrust depends on the speed and altitude of the flight, since the above factors affect the available thrust Рр and the aerodynamic quality K on the speed. To calculate the dependence of n at PREV it is necessary to have curves Рр (V) for different altitudes and a grid of polars.
For each speed value, the values of the available thrust are taken from the curve Pp (V), the value of the coefficient Cy is determined from the polar for the corresponding speed V, and calculated using formula (11.10).
When maneuvering in a horizontal plane with an overload less than available, but more than the maximum thrust, the aircraft will lose speed or flight altitude.
We've all heard the epic stories of people being shot in the head, falling from the 10th floor, or being lost at 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 or below sea level on Earth, 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 limits within which the average person can survive are fairly well defined. An example is the famous “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 rise before you suffocate? How much acceleration can your body withstand before it breaks apart?
Experiments conducted over decades have helped define the boundaries within which we live. Some of them were purposeful, some were accidental.
How long can we remain awake?
It is known that Air Force pilots, after three or four days of being awake, fell into such an uncontrollable state that they crashed their planes (falling asleep at the controls). Even one night without sleep affects a driver's ability 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 the fair scientific projects high school students in 1965. Before he fell asleep on the 11th day, he was essentially a plant with his eyes open.
But how long would it take for him to die?
In June this year, a 26-year-old Chinese man died after 11 days spent 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 establish the cause of death. But definitely not a single person died due to lack of sleep. And for obvious ethical reasons, scientists cannot determine this period in laboratory conditions.
But they were able to do it in rats. In 1999, sleep researchers at the University of Chicago placed rats on a spinning disk placed over a pool of water. They continuously recorded the rats' behavior using computer program capable of recognizing the onset of sleep. When the rat began to fall asleep, the disc would suddenly turn, waking it up, 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 body's resting metabolic rate 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) within 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 tries to repair itself during this time,” Caracappa explained.
By comparison, some workers at Japan's Fukushima nuclear power plant received between 0.4 and 1 Sv of radiation in an hour while confronting the accident last March. Although they survived, their risk of cancer was significantly increased, scientists say.
Even if nuclear accidents and supernova explosions are avoided, natural background radiation on Earth (from sources such as uranium in the soil, cosmic rays and medical devices) increases our chances of getting cancer in any year by 0.025 percent, Caracappa says. This sets a somewhat strange limit on human lifespan.
"The average person... exposed to an average dose of background radiation every year for 4,000 years, in the absence of other factors, will inevitably develop radiation-induced cancer," Caracappa says. In other words, even if we could defeat all diseases and turn off the genetic commands that control the aging process, we still would not live more than 4,000 years.
How much acceleration can we handle?
The ribcage protects our heart from strong impacts, but it is not a reliable protection against the jerks that have become possible today thanks to the development of technology. 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 space and air structures aircraft. (We don't want astronauts to lose consciousness 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 acting forces. According to a recent article published in the journal Popular Science, horizontal acceleration of 14 g can tear our organs apart from each other. 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 render you unconscious. (1 g is the force of gravity that we feel on the earth's surface; 14 g is the force of gravity on a planet 14 times more massive than ours.)
Acceleration directed forward or backward is most beneficial for the body, since the head and heart accelerate equally. The military's "human braking" experiments in the 1940s and 1950s (which essentially involved a rocket sled moving around Edwards Air Force Base in California) showed that we could brake at an acceleration of 45 g, and still be alive to tell the tale. With this kind of braking, when traveling at speeds above 600 mph, you can stop in a split second after traveling a few hundred feet. At 50 g of braking, experts estimate that we will probably turn into a bag of separate organs.
What environmental changes can we withstand?
Different people are able to withstand different changes in the usual atmospheric conditions, regardless of whether it is a change in temperature, pressure, or oxygen content in the air. The limits of survival are also related to how slowly environmental changes occur, since 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 of being in an extremely humid and hot environment (60 degrees Celsius). Establishing limits on death from chilling is more difficult. A person usually dies when their body temperature drops to 21 degrees Celsius. But how long this takes depends on how “used to the cold” a person is, and whether the mysterious, latent form of “hibernation” that is known to sometimes occur has manifested itself.
Survival boundaries are much better set for long-term comfort. According to a 1958 NASA report, humans can live indefinitely in environment, the temperature of which is between 4 and 35 degrees Celsius, provided that the latter temperature occurs in relative humidity no more than 50 percent. With lower humidity, the maximum temperature increases, since less moisture in the air facilitates the process of sweating, and thereby cooling the body.
As can be seen from science fiction films in which the astronaut's helmet opens outwards spaceship, we are unable to survive for long at very low levels of pressure or oxygen. At normal atmospheric pressure, air contains 21 percent oxygen. We will die from suffocation if the oxygen concentration drops below 11 percent. Too much oxygen also kills, gradually causing pneumonia over several days.
We pass out when our blood pressure drops below 57 percent atmospheric pressure, which corresponds to a rise to a height of 4500 meters. Climbers are able to climb higher mountains as their bodies gradually adapt to the reduced amount of oxygen, but no one can survive long enough without oxygen tanks at altitudes above 7,900 meters.
It's about 8 kilometers up. And there are still almost 46 billion light years left to the edge of the known universe.
Natalie Wolchover
"Life's Little Mysteries"
August 2012
Translation: Gusev Alexander Vladimirovich