Human mechanical parameters definition. Digest - industrial safety
Elective course
"Human Physics"
Explanatory note 2
Main course content 3-4
Thematic course planning 5
References 6
Explanatory note
In the physics course studied in modern schools, practically no attention is paid to the physical parameters that characterize a person. However, in connection with the study of psychological issues in school, modeling of processes occurring in living organisms, in technology, and the development of such a science as bionics, students are increasingly showing increased interest in the study of human physics.
While studying this course, students will not only satisfy their educational needs, but also gain research skills, become familiar with research methods in physics and biology, and receive brief information about medical and biological equipment. The skills acquired while working with measuring instruments, performing practical work and setting up experiments will be useful in further scientific and technical activities. An explanation of individual processes occurring in living organisms on the basis of physical laws will help them establish cause-and-effect relationships that exist in living and inanimate nature, and will generate interest not only in physics, but also in biology.
The course program is practice-oriented with elements of research activities.
Studying the elective course is designed for 17 hours, of which 7.3 hours (43%) for studying theoretical issues, 9.7 hours (57%) for practical classes (solving problems, performing laboratory work).
Main objectives of the course:
Show students the unity of the laws of nature, the applicability of the laws of physics to a living organism, the promising development of science and technology, and also show in which areas of professional activity the knowledge gained in the special course will be useful to them.
Create conditions for the formation and development of intellectual and practical skills among students in the field of physical experimentation.
Develop cognitive activity and independence, the desire for self-development and self-improvement.
Course objectives:
To promote the formation of cognitive interest in physics and the development of creative abilities in students.
Develop students' intellectual competence.
Develop skills in performing practical work and conducting research activities.
Improve skills in working with reference and popular science literature.
Upon completion of the course, students must know:
What physical laws can be used to explain the processes occurring in the human body.
Features of your body from the point of view of the laws of physics. be able to:
Work with various sources of information.
Observe and study phenomena, describe the results of observations.
Model phenomena, select the necessary instruments, perform measurements, present measurement results in the form of tables, graphs, set research problems.
MAIN COURSE CONTENT
The content of the course is qualitatively different from the basic physics course. In lessons, the laws of physics are discussed mainly in inanimate objects. However, it is very important that students gradually develop the conviction that the cause-and-effect relationship of phenomena is universal in nature and that all phenomena occurring in the world around us are interconnected. The course examines issues aimed at developing interest in physics, experimental activities, and developing the ability to work with reference literature. Upon completion of the course, students draw up a “Physical Passport of a Person.”
Human mechanical parameters 9h.
Physics. Human. Environment. Linear dimensions of various parts of the human body, their mass. Density of liquids and solid tissues that make up a person. Pressure force and pressure in living organisms.
Velocity of nerve impulses. Laws of blood movement in the human body. The body's natural defense against acceleration.
The manifestation of friction force in the human body, natural lubrication.
Maintaining balance by living organisms. Center of gravity of the human body. Levers in the human body. Walking man. Types of joints. Deformation of bones, tendons, muscles. Strength of biological materials. The structure of bones from the point of view of the possibility of greatest deformation.
The human body in the gravitational field of the Earth. Conditions for long-term human existence on a space station. Measures to protect pilots and astronauts from acceleration. Weightlessness and overload.
Work and power developed by a person in different types of activities. "Energy" and human development. Application of the law of conservation of energy to certain types of human movement.
Laboratory works.
1. Determining the volume and density of your body.
2. Determine the average speed of movement.
3. Determination of human reaction time.
4. Calibration of the dynamometer and determination of a person’s back strength.
5. Determination of the coefficients of friction of human shoe soles on various surfaces.
6. Determination of the power developed by a person.
Vibrations and waves in living organisms 2 hours.
Oscillations and man. Origin of biorhythms. Heart and sounds accompanying the work of the heart and lungs, their recording. Stethoscope and phonendoscope. Tapping is one of the ways to determine the size of internal organs and their condition. Radio waves and people.
Sound as a means of perception and transmission of information. Organ of hearing. Ultrasound and infrasound. Sound audibility range. Human vocal apparatus. Characteristics of the human voice. Hearing aid.
Laboratory work.
7. Study of the properties of the ear.
Thermal phenomena 2 hours.
Thermoregulation of the human body. The role of atmospheric pressure in human life. Osmotic pressure. Changes in blood pressure in the capillaries. Humidity. Respiratory system.
Thermal processes in the human body. Man is like a heat engine. Entropy and the human body. The second law of thermodynamics and the ability to self-organize.
Laboratory work.
8. Determination of the tidal volume of human lungs.
9. Determination of human blood pressure.
Electricity and magnetism 2 hours.
Electrical properties of the human body. Bioelectricity. Bacteria are the Earth's first electricians. Photoreceptors, electroreceptors, sleep bioelectricity. Electrical resistance of human organs to direct and alternating current. Magnetic field and living organisms.
Laboratory work.
10. Determination of human tissue resistance to direct and alternating electric current.
Human optical parameters 1 hour.
The structure of the human eye. The power of accommodation of the eye. Optical power. Visual defects and ways to correct them. Features of human vision. Resolution power of the human eye. How is it that we see. Gramophone record and eye. Why do we need two eyes? Spectral and energy sensitivity of the eye.
Laboratory work.
11. Observation of some psychophysiological features of human vision.
12. Determination of characteristic parameters of human vision.
Student Assessment System . After completing the course, credit is given if the following conditions are met:
1. Active participation in the preparation and conduct of seminars, conferences, publication of newspapers, and production of models.
2. Completion of at least half of the laboratory work.
3. Completion of at least one experimental task of a research or design nature.
4. Drawing up a “Physical Passport of a Person”.
THEMATIC COURSE PLANNING
Lesson topic
Number of hours
Total
theory
practice
HUMAN MECHANICAL PARAMETERS (9 H)
Physics. Human. Environment.
Kinematics and the human body.
Newton's laws in human life.
Man in conditions of weightlessness and
overloads
Upright posture and the human musculoskeletal system.
Manifestation of friction force in the human body.
Work and power developed by a person in different types of activities.
Statics in the human body.
Pressure and the human body.
VIBRATIONS AND WAVES IN LIVING ORGANISMS (2 hours)
Oscillations and man.
THERMAL PHENOMENA (1 H)
Thermal processes in the human body.
Second law of thermodynamics.
ELECTRICITY AND MAGNETISM. (2 hours)
Electrical properties of the human body
Magnetic field and living organisms.
OPTICAL PARAMETERS OF HUMAN (1 H)
Eye and vision
Conference.
Total:
BIBLIOGRAPHY
1. Agadzhanyan N.A. Rhythm of life and health. - M.: Knowledge, 1975.
2. Bezdenezhnykh E.A., Brickman I.S. Physics in wildlife and medicine. - Kyiv, 1976.
3. Bogdanov K.Yu. A physicist visiting a biologist. - M., 1986.
5. Berkinblit M.B. and others. Electricity in living organisms. - M.: Nauka, 1988.
6. Boyarova O. et al. From head to toe. - M.: Children's literature, 1967.
7. Bulat V.A. Optical phenomena in nature. - M.: Education, 1974.
8. Galperstein L. Hello physics! - M.: Education, 1973.
9. Gazenko O.G., Human safety and reliability in space flights. // Science and Life. -1984 No. 3.
10. Enochovich A.S. Handbook of Physics. - M.: Education, 1991.
11. Elkin V.I. Unusual educational materials in physics. - M.: Shkola-Press, 2001.
12.. Ilchenko V.R. Crossroads of physics, chemistry, biology. - M.: Education, 1986.
13. Katz Ts.B. Biophysics in physics lessons. - M.: Education, 1988.
14. Lanina I.Ya. Extracurricular work in physics. - M.: Education, 1977.
15. Lanina I.Ya. Not just a lesson. - M.: Education, 1991.
16. Manoilov V.E. Electricity and man. -L: Energoatomizdat, 1988.
17. Marion J.B. General physics with biological examples. - M., 1986.
18. Popular medical encyclopedia. - M., 1979.
19. Rydnik V.I. About modern acoustics. - M.: Education, 1979.
20. Sergeev B.A. Entertaining physiology. - M.: Education, 1977.
21. Silin A.A. Friction and us. - M., 1987.
22. Sinichkin V.P. Sinichkina O.P. Extracurricular work in physics. - Saratov: Lyceum, 2002.
23. Swarts Kl.E. Extraordinary physics of ordinary phenomena, - M., 1986.
24. Khutorskoy A.V., Khutorskaya L.N. Fascinating physics. - M.: ARKTI, 2000.
25. Khripkova A.G. Human physiology. - M.: Education, 1971.
26. I explore the world: Children's encyclopedia: Physics. - M.: AST, 1998.
27. World of physics. Entertaining stories about the laws of physics. St. Petersburg "MiM-Express". 1995
28. O.P. Spiridonov. LIGHT. Physics, information, life. M. "Enlightenment". 1993
To evaluate the performance properties of products and determine the physical and mechanical characteristics of materials, various instructions, GOSTs and other regulatory and advisory documents are used. Methods for testing the destruction of a whole series of products or similar material samples are also recommended. This is not a very economical method, but it is effective.
Definition of characteristics
The main characteristics of the mechanical properties of materials are as follows.
1. Temporary resistance or tensile strength is the stress force that is recorded at the highest load before the sample fails. Mechanical characteristics of strength and plasticity of materials describe the properties of solids to resist irreversible changes in shape and destruction under the influence of external loads.
2. The conditional stress is when the residual deformation reaches 0.2% of the length of the sample. This is the lowest stress while the sample continues to deform without a noticeable increase in loads.
3. The long-term strength limit is the maximum stress that, at a given temperature, causes destruction of the sample over a certain time. Determination of the mechanical characteristics of materials is guided by the ultimate units of long-term strength - destruction occurs at 7,000 degrees Celsius in 100 hours.
4. The conditional creep limit is the stress that causes a given elongation in the sample at a given temperature for a certain time, as well as the creep rate. The limit is considered to be metal deformation in 100 hours at 7,000 degrees Celsius by 0.2%. Creep is a certain rate of deformation of metals under constant loading and high temperature for a long time. Heat resistance is the resistance of a material to fracture and creep.
5. The endurance limit is the highest value of the cycle stress when fatigue failure does not occur. The number of loading cycles can be specified or arbitrary, depending on how the mechanical tests of the materials are planned. Mechanical properties include fatigue and endurance of the material. Under the influence of loads in the cycle, damage accumulates and cracks form, leading to destruction. This is fatigue. And the property of resistance to fatigue is endurance.
Tension and compression
Materials used in engineering practice are divided into two groups. The first is ductile, for which significant residual deformations must appear to fail, the second is brittle, which collapses at very small deformations. Naturally, such a division is very arbitrary, because each material, depending on the conditions created, can behave both as brittle and as ductile. This depends on the nature of the stress state, on temperature, on the rate of deformation and other factors.
The mechanical characteristics of materials under tension and compression are eloquent for both ductile and brittle ones. For example, low-carbon steel is tested in tension, and cast iron is tested in compression. Cast iron is brittle, steel is ductile. Brittle materials have greater resistance to compression, but less resistance to tensile deformation. Plastic materials have approximately the same mechanical characteristics under compression and tension. However, their threshold is still determined by stretching. It is through these methods that the mechanical characteristics of materials can be more accurately determined. The tension and compression diagram is presented in the illustrations for this article.
Fragility and ductility
What is ductility and fragility? The first is the ability not to collapse, receiving residual deformations in large quantities. This property is decisive for the most important technological operations. Bending, drawing, drawing, stamping and many other operations depend on the plasticity characteristics. Ductile materials include annealed copper, brass, aluminum, mild steel, gold, and the like. Bronze and duralumin are much less ductile. Almost all alloy steels are very weakly ductile.
The strength characteristics of plastic materials are compared with the yield strength, which will be discussed below. The properties of brittleness and ductility are greatly influenced by temperature and loading rate. Fast tension imparts brittleness to the material, while slow tension imparts ductility. For example, glass is a fragile material, but it can withstand prolonged exposure to load if the temperature is normal, that is, it shows plasticity properties. It is plastic, but under a sharp shock load it appears as a brittle material.
Oscillation method
The physical and mechanical characteristics of materials are determined by the excitation of longitudinal, bending, torsional and other, even more complex ones, depending on the size of the samples, shapes, types of receiver and exciter, methods of fastening and schemes for applying dynamic loads. Large-sized products are also subject to testing using this method, if the application method is significantly changed in the methods of applying load, exciting vibrations and recording them. The same method is used to determine the mechanical characteristics of materials when it is necessary to evaluate the rigidity of large structures. However, when locally determining material characteristics in a product, this method is not used. The practical application of the technique is possible only when the geometric dimensions and density are known, when it is possible to fix the product on supports, and on the product itself - converters, certain temperature conditions are needed, etc.
For example, when temperature conditions change, one change or another occurs, and the mechanical characteristics of materials become different when heated. Almost all bodies expand under these conditions, which affects their structure. Any body has certain mechanical characteristics of the materials from which it consists. If these characteristics do not change in all directions and remain the same, such a body is called isotropic. If the physical and mechanical characteristics of materials change - anisotropic. The latter is a characteristic feature of almost all materials, just to varying degrees. But there are, for example, steels where the anisotropy is very insignificant. It is most clearly expressed in natural materials such as wood. In production conditions, the mechanical characteristics of materials are determined through quality control, where various GOSTs are used. The heterogeneity estimate is obtained from statistical processing when the test results are summed up. Samples must be numerous and cut from a specific structure. This method of obtaining technological characteristics is considered quite labor-intensive.
Acoustic method
There are quite a lot of acoustic methods for determining the mechanical properties of materials and their characteristics, and they all differ in the methods of input, reception and recording of vibrations in sinusoidal and pulsed modes. Acoustic methods are used to study, for example, building materials, their thickness and stress state, and during flaw detection. The mechanical characteristics of structural materials are also determined using acoustic methods. Numerous different electronic acoustic devices are now being developed and mass-produced, which make it possible to record elastic waves and their propagation parameters in both sinusoidal and pulsed modes. On their basis, the mechanical characteristics of the strength of materials are determined. If low-intensity elastic vibrations are used, this method becomes absolutely safe.
The disadvantage of the acoustic method is the need for acoustic contact, which is not always possible. Therefore, this work is not very productive if there is an urgent need to obtain mechanical characteristics of the strength of materials. The result is greatly influenced by the condition of the surface, the geometric shapes and dimensions of the product being tested, as well as the environment where the tests are carried out. To overcome these difficulties, a specific problem must be solved using a strictly defined acoustic method or, on the contrary, using several of them at once, it depends on the specific situation. For example, fiberglass plastics lend themselves well to such research, since the propagation speed of elastic waves is good, and therefore through sounding is widely used, when the receiver and emitter are located on opposite surfaces of the sample.
Flaw detection
Flaw detection methods are used to control the quality of materials in various fields of industry. There are non-destructive and destructive methods. Non-destructive ones include the following.
1. To determine cracks on surfaces and lack of penetration, it is used magnetic flaw detection. Areas that have such defects are characterized by scattering fields. They can be detected with special devices or simply by applying a layer of magnetic powder to the entire surface. In areas of defects, the location of the powder will change even during application.
2. Flaw detection is also carried out using ultrasound. The directed beam will be reflected (scattered) differently if there are any discontinuities even deep inside the sample.
3. Defects in the material are clearly shown radiation research method, based on the difference in radiation absorption by media of different densities. Gamma flaw detection and X-ray are used.
4. Chemical flaw detection. If the surface is etched with a weak solution of nitric, hydrochloric acid or a mixture of them (regia vodka), then in places where there are defects, a mesh in the form of black stripes appears. You can use a method in which sulfur prints are removed. In places where the material is heterogeneous, the sulfur should change color.
Destructive methods
Destructive methods have already been partially discussed here. Samples are tested for bending, compression, tension, that is, static destructive methods are used. If the product is tested with variable cyclic loads on impact bending, the dynamic properties are determined. Macroscopic methods paint a general picture of the structure of a material in large volumes. For such a study, specially ground samples are needed that are etched. Thus, it is possible to identify the shape and location of grains, for example, in steel, the presence of deformed crystals, fibers, cavities, bubbles, cracks and other inhomogeneities of the alloy.
Microscopic methods are used to study the microstructure and identify the smallest defects. The samples are pre-ground, polished and then etched in the same way. Further testing involves the use of electrical and optical microscopes and X-ray diffraction analysis. The basis of this method is the interference of rays that are scattered by atoms of matter. The characteristics of the material are monitored by X-ray diffraction analysis. The mechanical characteristics of materials determine their strength, which is the main thing for building structures that are reliable and safe to use. Therefore, the material is tested carefully and using different methods in all states that it can accept without losing a high level of mechanical characteristics.
Control methods
To carry out non-destructive testing of the characteristics of materials, the correct choice of effective methods is of great importance. The most accurate and interesting in this regard are flaw detection methods - defect control. Here it is necessary to know and understand the differences between the methods of implementing flaw detection methods and methods for determining physical and mechanical characteristics, since they are fundamentally different from each other. If the latter are based on monitoring physical parameters and their subsequent correlation with the mechanical characteristics of the material, then flaw detection is based on the direct conversion of radiation that is reflected from a defect or passes through a controlled environment.
The best thing, of course, is comprehensive control. Complexity lies in determining the optimal physical parameters, which can be used to identify the strength and other physical and mechanical characteristics of the sample. And also, an optimal set of means for controlling structural defects is simultaneously developed and then implemented. And finally, an integral assessment of this material appears: its performance is determined according to a whole set of parameters that helped determine non-destructive methods.
Mechanical tests
With the help of such tests, the mechanical properties of materials are checked and evaluated. This type of control appeared a long time ago, but has not yet lost its relevance. Even modern high-tech materials are criticized quite often and fiercely by consumers. This suggests that examinations should be carried out more carefully. As already mentioned, mechanical tests can be divided into two types: static and dynamic. The former check the product or sample for torsion, tension, compression, bending, and the latter check for hardness and impact strength. Modern equipment helps to perform these not very simple procedures efficiently and identify all the performance properties of a given material.
A tensile test can determine the resistance of a material to the effects of applied constant or increasing tensile stress. The method is old, tried and true, used for a very long time and is still widely used. The sample is stretched along the longitudinal axis by means of a device in the testing machine. The rate of stretching of the sample is constant, the load is measured by a special sensor. At the same time, the elongation is monitored, as well as its compliance with the applied load. The results of such tests are extremely useful if new structures need to be created, since no one yet knows how they will behave under load. Only identifying all the elasticity parameters of the material can give a hint. Maximum stress - yield strength determines the maximum load that a given material can withstand. This will help calculate the safety factor.
Hardness test
The stiffness of a material is calculated by The combination of fluidity and hardness helps determine the elasticity of the material. If the technological process involves operations such as drawing, rolling, pressing, then it is simply necessary to know the magnitude of possible plastic deformation. With high plasticity, the material can take any shape under appropriate load. A compression test can also be used to determine the safety factor. Especially if the material is fragile.
Hardness is tested using an identifier, which is made of a much harder material. Most often it is carried out using the Brinell method (a ball is pressed in), Vickers (a pyramid-shaped identifier) or Rockwell (a cone is used). An identifier is pressed into the surface of the material with a certain force for a certain period of time, and then the imprint remaining on the sample is examined. There are other fairly widely used tests: impact strength, for example, when the resistance of a material is assessed at the moment a load is applied.
With your feet resting on the globe,
I hold the ball of the sun in my hands.
I am like a bridge between the Earth and the Sun,
And for me the Sun descends to Earth,
And the Earth rises towards the Sun.
So I stand...I, Man.
E. Mezhelaitis
Many sciences study man: philosophy, history, anthropology, biochemistry... etc. But only by considering the human phenomenon holistically will we be able to formulate an answer to the question: “What is a person?”
How does our body work?
How does he work?
What's good for your health?
What is life-threatening?
Let's try to rummage through the literature and figure it out!
Do you know about the interesting features of our body?
Human DNA contains about 80,000 genes.
In ancient Rome, people lived on average no more than 23 years, and in the 19th century in the United States, the average life expectancy did not exceed 40 years.
Men are considered dwarfs if their height is below 130 cm, women - below 120 cm.
The human body consists of 639 muscles.
When a person smiles, 17 muscles “work.”
In the human spine 33 or 34 vertebrae.
At birth, a child’s body contains about 300 bones; by adulthood, only 206 remain.
Almost half of all human bones are found in the wrists and feet.
Fingernails grow approximately 4 times faster, than on your feet.
Human bones are 50% water.
Each human finger bends approximately 25 million times during a lifetime.
The human body contains only 4 minerals: apatite, aragonite, calcite and cristobalite.
Children are born without kneecaps. They appear only at the age of 2-6 years.
The human eye is capable of distinguishing 10,000,000 shades of color.
The phenomenon in which a person loses the ability to see due to strong light is called “snow blindness.”
On average, you secrete 5 milliliters of tears - that's a large bottle in a year.
By blinking 20 times a minute, you moisturize your eyes. This amounts to more than 10 million muscular contractions per year.
It is impossible to sneeze with your eyes open.
Women blink approximately 2 times more often than men.
Men are about 10 times more likely than women to suffer from color blindness.
People with blue eyes more sensitive to pain than everyone else.
A person blinks on average every 6 seconds, which means that throughout our lives we lower and raise our eyelids about 250 million times.
On average, human hair grows at a rate of 12 mm per month.
Blondes grow a beard faster than brunettes.
Human hair is approximately 5,000 times thicker than soap film.
At rest, you inhale and exhale 16 times per minute, during which time 8 liters of air pass through your lungs. In a year, this amount of air could fill two balloons.
The surface of the lungs is about 100 square meters.
The right lung of a person holds more air than the left.
An adult takes approximately 23,000 breaths (and exhalations) per day.
The surface area of human lungs is approximately equal to tennis court area.
The strongest muscle in the human body is the tongue.
There are about 2000 taste buds in the human body.
There are about 40,000 bacteria in the human mouth. The average human brain weighs about 1.3 kg.
The human brain generates more electrical impulses per day than all the world's phones combined.
From the moment of birth, there are already 14 billion cells in the human brain, and this number does not increase until death. On the contrary, after 25 years it decreases by 100 thousand per day.
In the minute you spend reading a page, about 70 cells die.
After 40 years, brain degradation accelerates sharply, and after 50, neurons (nerve cells) dry out and brain volume decreases.
In the human brain, 100,000 chemical reactions occur in one second.
Man is the only representative of the animal world capable of drawing straight lines.
The length of hair on the head grown by the average person over the course of a lifetime is 725 kilometers.
You can lose 150 calories per hour by hitting your head against a wall.
Small blood vessels-capillaries are 50 times thinner than the thinnest human hair.
The average capillary diameter is approximately 0.008mm.
Young skin contains an incredible amount of water - 8 liters.
Every day you lose up to 2 liters through your skin. Since the process of skin cell death takes 120 days, this means you change your skin three times in a year.
During a lifetime, a person's skin changes approximately 1000 times.
Your heart beats 80 times per minute at rest, pumping 5 liters of blood.
In a year, the heart makes 42 million contractions and pumps enough blood to fill several swimming pools.
36,800,000 - the number of heartbeats in a person in one year.
The size of a person's heart is approximately equal to the size of his fist.
The weight of an adult human heart is 220-260 g. Nerve impulses in the human body move at a speed of approximately 90 meters per second.
There are about 75 kilometers (!) of nerves in the adult human body.
Human gastric juice contains 0.4% hydrochloric acid(HCl).
Humans have approximately 2 million sweat glands. The average adult loses 540 calories with every liter of sweat.
Men sweat about 40% more than women.
During life, the human small intestine is about 2.5 meters long.
After his death, when the muscles of the intestinal wall relax, its length reaches 6 meters.
The total weight of bacteria living in the human body is 2 kilograms.
A person is able to recognize only five odors: floral, specific (lemon, apple, etc.), burnt (coffee, etc.), rotten (rotten eggs, cheese, etc.) and ethereal (gasoline, alcohol) .
A person who gets lost during thick fog or a blizzard almost always walks in a circle, which is explained by the asymmetry of our body, that is, the lack of complete balance between the right and left halves of the human body.
A person, it turns out, trembles only to keep warm.
A person who smokes a pack of cigarettes a day drinks half a cup of tar a year.
How does a person tolerate different altitudes above sea level?
The death zone is more than 8 km: a person can stay at this altitude without a breathing apparatus for only a short time - 3 minutes, and at an altitude of 16 km - 9 seconds, after which death occurs.
Critical zone - from 6 to 8 km: serious functional disorders of the body.
Zone of incomplete compensation - from 4 to 5 km: deterioration in general well-being.
The zone of full compensation is from 2 to 4 km: some disturbances in the activity of the heart, sensory organs and other systems, thanks to the mobilization of the body's reserve forces, quickly disappear.
The safe zone is from 1.5 to 2 km: there are no significant disruptions in the functioning of the human body.
Temperatures that are critical for the human body
(at normal pressure and relative humidity)
Normal temperature for most people is from 36.3 to 37C
Critical temperature accompanied by loss of consciousness - above 42C
Lethal temperature - above 43C
Temperature leading to a slowdown in brain processes - below 34C
Critical temperature accompanied by loss of consciousness - below 30C
Lethal temperature, cardiac fibrillation occurs, blood circulation stops - below 27C
Basic physical parameters of blood.
All parameters are given for body temperature - 37C
Density - 1050 kg/cub.m
Viscosity - 0.004 Pa.s
Blood plasma viscosity - 0.0015 Pa.s
Hemoglobin diffusion coefficient in water - 0.00000000007 sq.m.
Surface tension 0.058 N/m
Freezing (melting) temperature - minus 0.56C
Specific heat capacity - 3000 J/kg.K
Electrical characteristics of human body tissues
Resistivity:
...muscles - 1.5 Ohm.m
...blood - 1.8 Ohm.m
...leather - №№0000 Ohm.m
...bone - 1000000 Ohm.m
...blood -85.5
...skin - from 40 to 50
...bone - from 6 to 10
Heat transfer from the human body
Loss of energy from the total balance:
...for respiration and evaporation of water - 13%
...on the work of internal organs and systems - 1.87%
...for heating exhaled air - 1.55%
...for the evaporation of water from the surface of the skin - 20.7%
...for heating the surrounding space - 30.2%
... for radiation - 43.8%
Human mechanical parameters
The average density of a person is 1036 kg cubic m
Average blood speed:
...in arteries - from 0.2 to 0.5 m s
...in the veins - from 0.1 to 0.2 m s
The speed of spread of irritation along the nerves is from 400 to 1000 m s
Force developed by the beating heart:
...in the initial phase of contraction - 90 N
...in the final phase of contraction - 70N
Heart work per day - 86400 J
Mass of blood ejected by the heart per day - 5200 kg
Power developed during fast walking - 200 W
Human electrical parameters
Specific resistance of body tissues:
...top layer of dry skin - 330000 Ohm.m
...blood - 1.8 Ohm.m
...muscles - 1.5 Ohm.m
The dielectric constant:
...dry skin - from 40 to 50
...blood - 85
Human resistance from the end of one hand to the end of the other (with dry skin) - 15000 Ohms
Current flow through the human body:
...safe - less than 0.001 A
... life-threatening - more than 0.05 A
Safe electrical voltage:
...dry room - less than 12 V
...damp room - less than 36 V
Human optical parameters
Duration of retention of visual sensation by the eye - 0.14 s
The diameter of the eyeball of an adult is 25 mm
Refractive index of the lens - 1.4
Optical power:
...lens - from 19 to 33 diopters
...total eyes - 60 diopters
Pupil diameter:
...in daylight - 2 mm
...in night lighting - from 6 to 8 mm
Intraocular pressure - 104 kPa (780 mm Hg)
The number of rods in the retina is 130 million
The number of cones in the retina is 7 million
The minimum size of the image on the retina at which two points of an object are perceived separately is 0.002 mm
The wavelength of light to which the eye is most sensitive is 555 mm
Human radiation parameters
Permissible radiation dose - up to 0.25 Gy
Radiation dose causing radiation sickness - from 1 to 6 Gy
Lethal dose of radiation - from 6 to 10 Gy
“All bodies, the firmament, the stars, the Earth and its kingdoms cannot be compared with the lowest of minds, for the mind carries within itself the knowledge of all this, but the bodies know nothing.”
Introduction…………………………………………………………… .
I.Human physics
1.1. Simple mechanisms in the human body…………………
1.2. Deformations in the human body…………………………..
1.3. Human circulatory system………………………….
1.4. Diffusion in the human body……………………………..
1.5. Human adaptation to different temperatures……….
1.6. Air humidity and its role in the human body………..
1.7. The law of conservation and transformation of energy in the human body ……………………………………………………….
1.8. Electrical phenomena in the human body……………...
1.9. Fluctuations in the human body…………………………….
1.10. Electromagnetic radiation in the human body………
II.Research part
Conclusion…………………………………………………………
Literature
INTRODUCTION
When studying a physics course, we, for the most part, consider inanimate nature, and talk about living nature in passing. But, at the same time, living nature is so unique and all the laws of mechanics, electrostatics, optics, acoustics, thermodynamics and nuclear physics apply in it.
So a bee sat on a flower and accidentally touched the stamen, the anther of which hit it on the back and the pollen spilled out. A biologist will see in this example the process of pollination of a plant, while a physicist will pay attention to the nature of the movement of the bee, the sound it makes, the action of the lever - the stamen and the free fall of pollen.
And what can we say about the human body itself! There are so many physical phenomena here, such a field of activity!
Here the choir is singing a song. The musician will immediately pay attention to the notes produced by the singers, the pitch of the voices, the volume and harmony of the song. The physicist will see in this the oscillatory movement of the vocal cords, the propagation of sound waves in the medium and their interference, as well as the vibration of the eardrum in the listener’s ear.
In my work, I just wanted to look at the human body through the eyes of a physicist, and also to study myself, as far as possible within the framework of a school physics laboratory. In addition to physics, my work will be closely related to a number of school subjects: biology, chemistry, physical education and music.
I. HUMAN PHYSICS
1.1. SIMPLE MECHANISMS IN THE HUMAN BODY
In the human body, all bones that have some freedom of movement are levers. For example, the bones of the limbs, the lower jaw, the skull (the fulcrum is the first spine), the phalanges of the fingers. Skeletal linkages are usually designed to gain speed at a loss of strength. The ratio of the length of the arms of the lever element of the skeleton is closely dependent on the vital functions performed by this organ. Let us consider the conditions for equilibrium of a lever using the example of a skull (Fig. 1). Here the axis of rotation of the lever O passes through the articulation of the skull with the first vertebra. In front of the fulcrum, on a relatively short shoulder, the force of gravity of the head R acts, behind - the force F of the traction of the muscles and ligaments attached to the occipital bone.
Another example of the operation of a lever is the action of the arch of the foot when lifting onto the half toes (Fig. 2). The support O of the lever, through which the axis of rotation passes, is the heads of the metatarsal bones.
The resisting force R - the weight of the entire body - is applied to the talus. The effective muscular force F, carried out by lifting the body, is transmitted through the Achilles tendon and is applied to the protrusion of the heel bone.
Flexible organs are common in nature and can change their curvature within a wide range (spine, fingers). Their flexibility is due either to the combination of a large number of short levers with a rod system, or to the combination of elements that are relatively flexible with intermediate elements that are easily deformed. Bending control is achieved by a system of longitudinal or oblique rods (Fig. 3, 4).
“Pitting weapons”: nails and teeth – shaped like a wedge (a modified inclined plane). Many of these wedges have very smooth hard surfaces (minimum friction), which is what makes them very sharp (Fig. 5)
1.2. DEFORMATIONS IN THE HUMAN BODY.
The human body experiences quite a large mechanical load from its own weight and from muscle efforts that arise during work. It is interesting that using the example of the human body, all types of deformation can be traced. Compression deformations are experienced by the spinal column, lower limbs and foot coverings; sprains - upper limbs, ligaments, tendons, muscles; bending deformities – spine, pelvic bones, limbs; torsional deformations - neck when turning the head, torso in the lower back when turning, hands when rotating, and so on.
The table shows the strength limits of various types of tissues of the human body and substances for various types of deformation.
Type of fabric or substance | Tensile strength, N/m2 | Compressive strength, N/m2 |
|
Compact bone substance | |||
Coarse fibrous connective tissue (tendons, ligaments) | |||
Nerve tissue | |||
Muscle | |||
The table shows that the modulus of elasticity for a bone or tendon when stretched is very high, but for muscles, veins, and arteries it is very small. The maximum stress that destroys the humerus bone is about 8 * 107 N\ m2.
Connective tissues in ligaments, lungs, etc. have great elasticity, for example, the nuchal ligament can be stretched more than twice.
Torsional resistance increases very quickly with increasing thickness, so organs designed to perform torsional movements tend to be long and thin (neck).
When deflecting, the material is stretched along its convex side and compressed along its concave side; the middle parts do not experience noticeable deformation.
Therefore, in technology, solid beams are replaced with pipes, beams are made into T-bars or I-beams; This saves material and reduces the weight of installations. As you know, the bones of the limbs have a tubular structure. A beam, arched upward and having reliable supports that do not allow its ends to move apart (arch), has enormous strength in relation to the forces acting on its convex side (architectural vaults, barrels, in organisms - the skull-chest).
The building art of nature and people develops according to the same principle - saving materials and energy. It is known that hard material in bones is located in accordance with the directions of principal stresses. This can be detected if we consider a longitudinal section of the upper part of the femur (Fig. 6) and a curved beam bending under the influence of a load distributed over a certain area of the upper surface. Interestingly, the steel Eiffel Tower resembles in its structure the tubular bones of a person (femur or tibia). There is a similarity in the external shapes of the structures, and in the angles between the “crossbeams” and “beams” of the bone and the braces of the tower.
1.3. HUMAN CIRCULAR SYSTEM.
During operations on the heart, there is often a need to temporarily turn it off from the blood circulation and operate on a dry heart (Fig. 7). The artificial circulation machine reliably maintains the specified minute volume of blood circulation in the body throughout the entire process (about 4 - 5 liters for an adult patient) and the specified temperature of the circulating blood.
The heart-lung machine consists of two main parts: a pump system and an oxygenator. The pumps perform the functions of the heart - they maintain pressure and blood circulation in the vessels of the body during surgery. The oxygenator performs the functions of the lungs and ensures blood saturation with oxygen of at least 95% and maintains the partial pressure of CO2 at the level of millimeters of mercury. Venous blood from the patient’s vessels is transfused by gravity into an oxygenator located below the level of the operating table, where it is saturated with oxygen, freed from excess carbon dioxide, and then pumped into the patient’s bloodstream by an arterial pump. AIK can replace the functions of the heart and lungs for a short time. Currently, almost all heart surgeries are performed using a cardiopulmonary bypass. In some cases, the operation is performed with moderate hypothermia (decrease in temperature) of the body, which makes it possible to use AIC for a longer time.
Currently, medical scientists and engineers are working on the creation and use of an artificial heart device.
By revising capillary phenomena Their role in biology should be emphasized, since most tissues are penetrated by a huge number of capillary vessels. It is in the capillaries that the main processes associated with respiration and nutrition of the body take place, as well as all the complex chemistry of life, closely related to diffusion phenomena.
Let us present some data for the human body.
The cross-sectional area of the aorta is 8 cm2, and the total area of all capillaries is approximately 3200 cm2, that is, the area of the capillaries is 400 times greater than the area of the aorta. Accordingly, the blood flow speed decreases - from 20 cm/s at the beginning of the aorta to 0.05 cm/s in the capillary.
The diameter of each capillary is 50 times smaller than the diameter of a human hair, and its length is less than 0.5 mm. There are 160 billion capillaries in the adult human body.
The total length of the capillaries reaches 60-80 thousand km; On average, up to 2 thousand capillaries pass through each square millimeter of the cross section of the heart muscle
A physical model of the cardiovascular system can be a system of many branched tubes with elastic walls. As they branch, the total cross-section of the tubes increases and the speed of fluid movement decreases accordingly. However, due to the fact that the branching consists of many narrow channels, losses due to internal friction greatly increase and the overall resistance to the movement of liquids (despite the decrease in speed) increases significantly.
1.4. DIFFUSION IN THE HUMAN BODY
The greatest absorption of food occurs in the small intestines, the walls of which are specially adapted for this. The internal surface area of the human intestine is 0.65 m2. It is covered with villi - microscopic formations of the mucous membrane 0.2-1 mm high, due to which the actual surface area of the intestine reaches 4-5 m2, that is, 2-3 times the surface area of the entire body. And in the process of absorption, diffusion plays an important role.
BREATHING - the transfer of oxygen from the environment into the body through its integuments - occurs the faster, the larger the surface area of contact between the body and the environment, and the slower, the thicker and denser the integuments of the body. From this it is clear that small organisms, in which the surface area is large compared to the volume of the body, can do without special respiratory organs at all, being satisfied with the flow of oxygen exclusively through the outer shell (if it is sufficiently thin and moisturized). In larger organisms, breathing through the skin may be more or less sufficient only if the integument is extremely thin; with coarse integument, special respiratory organs are necessary. The main physical requirements for these organs are maximum surface and minimum thickness and moisture content of the integument. The first is achieved by numerous branches or folds (pulmonary alveoli, fringed shape of the gills).
How does a person breathe? In humans, the entire surface of the body takes part in breathing - from the thickest epidermis of the heels to the hairy scalp. The skin on the chest, back and stomach breathes especially intensely. Interestingly, these areas of the skin are significantly more intense than the lungs in terms of breathing intensity. With the same size respiratory surface, oxygen can be absorbed here by 28%, and carbon dioxide can be released even 54% more than in the lungs. However, in the entire respiratory process, the participation of the skin is negligible compared to the lungs, since the total surface area of the lungs, if you expand all 700 million alveoli, microscopic bubbles, through the walls of which gas exchange occurs between air and blood, is about 90-100 m2, and the total area The surface area of human skin is about 90-100 m2, that is, 45-50 times less.
Rhythmic breathing of the chest is not yet breathing, but it provides breathing. When you inhale, due to the work of the intercostal muscles, the volume of the chest increases. In this case, the air pressure in the lungs drops below atmospheric pressure: due to the resulting pressure difference, inhalation occurs. Then, due to muscle relaxation, the volume of the chest decreases, the pressure in the lungs becomes higher than atmospheric pressure - exhalation occurs. Figure 8 shows a diagram of gas exchange in the lungs. This shows the diffusion of oxygen O2 and carbon dioxide CO2 through the walls of the alveoli.
CAISON DISEASE. The most intense diffusion occurs between gases or between gas and liquid. Gases are adsorbed on the surface of the liquid and then spread through diffusion throughout its entire mass, in other words, dissolve in it. At not too high pressures, the mass of gas dissolving in a liquid is directly proportional to the partial pressure of the gas above it. When the gas pressure above the surface of the liquid decreases, the gas dissolved in it is released in the form of bubbles. This phenomenon underlies decompression sickness, which affects divers. It is known that at depths under water, a diver breathes air at elevated pressure and his blood is saturated with air gases, especially nitrogen. As a result of a sharp decrease in pressure upon returning to the surface of the water, nitrogen is released from the blood in the form of bubbles that can enter a small blood vessel. In this case, complete blockage of blood vessels may occur. This phenomenon is called gas embolism. Blockage of blood vessels in vital organs can have serious consequences for the body. To avoid this, you have to return the diver to the surface very slowly (after working at a depth of 80 m for 1 hour, it takes about 9 hours to rise) or use special decompression chambers. Currently, devices are being developed using a helium-oxygen mixture, which make it possible for the diver to return to the surface more quickly.
1.5. HUMAN ADAPTATION TO DIFFERENT TEMPERATURES.
Due to the properties of the cytoplasm of cells, all living things are capable of living at temperatures between 0 and 500 C. Most habitats on the surface of our planet have a temperature within these limits; for each species, going beyond these limits means death either from cold or heat.
In order to keep body temperature constant, a person must either reduce heat loss with effective protection or increase heat production. This is achieved in very different ways. First of all, protective cover is important. Human protective clothing is that they delay convection currents, slow down evaporation, weaken or completely stop radiation emission. The protective role of fat is also well known. There are various mechanisms for maintaining heat in unprotected areas, operating due to heat exchange in the bundles of blood vessels where veins and arteries come into contact. It turns out that the colder the climate, the shorter the ears. The fight against overheating is carried out mainly by increasing evaporation. Various conditions that impede evaporation disrupt the regulation of heat transfer from the body. Thus, leather, rubber, oilcloth, synthetic clothing makes it difficult to regulate the heat temperature. Sweating plays an important role in the thermoregulation of the body; it ensures the constancy of the body temperature of a person or animal. Due to the evaporation of sweat, internal energy decreases, thanks to which the body cools.
WHY DO WE BLUE RED IN THE HEAT, AND WHEN WE GO PALER AND SHAKE IN THE COLD? This is explained as follows. The normal ambient temperature for humans is 18-200C. If it becomes above 250C, then the skin nerve endings that perceive thermal irritation are excited, and thanks to signals from the central nervous system, skin vessels dilate. More blood flows into the skin from internal organs, and it turns red. At low ambient temperatures, the body begins to give off most of its heat through conduction and radiation. The skin receives heat mainly from the flowing blood. To reduce heat transfer, the blood vessels narrow, which is why we turn pale. When we are cold, our body increases the release of energy into the muscles due to the random contraction of individual groups of muscle fibers, which we call shivering.
1.6. AIR HUMIDITY AND ITS ROLE IN THE BODY
PERSON.
Air with a relative humidity of 40 to 60% is considered normal for human life. When the environment is at a temperature higher than the human body, increased sweating occurs. Excessive sweating leads to cooling of the body and helps to work in high temperature conditions. However, such active sweating is a significant burden for a person! If at the same time the absolute humidity is high, then living and working becomes even harder (humid tropics, some workshops, for example dyeing).
Relative humidity below 40% at normal air temperatures is also harmful, as it leads to increased loss of moisture from the body, which leads to dehydration.
1.7. LAW OF CONSERVATION AND TRANSFORMATION OF ENERGY
IN HUMAN LIFE.
When studying the law of conservation and transformation of energy, it is important to emphasize the role of the scientist R. Mayer, who was the first to formulate it from the position of a physician-naturalist. His attention was attracted by phenomena occurring in the human body. He noticed the difference in the color of venous blood in countries of the temperate and tropical zones and came to the conclusion that the “temperature difference” between the body and the environment should be in quantitative relation to the difference in the color of both types of blood, that is, arterial and venous. This difference in color is an expression of the amount of oxygen consumed, or the intensity of the combustion process occurring in the body. Interpreting these observations on the basis of the principle that “nothing comes from nothing and nothing turns into nothing and that cause is equal to effect,” already in 1841. Mayer expressed the basic idea of the law of conservation and transformation of energy.
A number of Mayer's studies are devoted to identifying energy processes. Mayer believed that the source of mechanical and thermal effects in a living organism are the chemical processes occurring in it as a result of the absorption of oxygen and food
In setting out the law of conservation and transformation of energy, it is desirable to illustrate its application of the transformation of one type of energy into another, occurring in living organisms. To do this, you can use a table that shows the various energy transformations in living cells.
TRANSFORMATION | WHERE DOES IT HAPPEN? |
Nerve cells, brain |
|
Sound energy into electrical energy | Inner ear |
Light energy into electrical energy | Retina |
Chemical energy into mechanical energy | Muscle cells, ciliated epithelia |
Chemical energy into electrical energy | Organs of taste and smell |
It is important to note that any living organism is an open thermodynamic system, far from a state of equilibrium. It is also interesting to make calculations of energy transformations in a living organism and determine the efficiency of some biological processes. We know that work can be done either by changing the internal energy of the system, or by imparting a certain amount of heat to the system.
In a living system, regardless of whether it is a whole organism or individual organs (for example, muscles), work cannot be done due to the influx of heat from the outside, that is, a living organism cannot work as a heat engine. This can be shown by a simple calculation. It is known that a heat engine
where T1 and T2 are the temperatures of the heat source and refrigerator, respectively, in the absolute temperature scale.
Let's try to determine the muscle temperature (T1), assuming that it works like a heat engine, at a temperature of 250C with an efficiency of 30%. Substituting the temperature of the refrigerator T2 = 298 K into the formula and assuming efficiency = 1 /3, we get
T1 – 298 K 1
from where T1 = 447K, or 1740C. Thus, if the muscle worked like a heat engine, it would heat up under these conditions to a temperature of 1740C. This, of course, is unrealistic, since proteins are known to denature at temperatures around 500C. Thus, in a living organism, work is done by changing the internal energy of the system.
The validity of the first law of thermodynamics for biology can be proven if a living organism is isolated from its environment, the amount of heat it releases is changed, and it is compared with the thermal effect of biochemical reactions inside the organism. For this purpose, back in 1780, Lavoisier and Laplace placed a guinea pig in a calorimeter and measured the amount of heat and carbon dioxide released. After this, the amount of heat released during direct combustion of the original food products was determined. In both cases the values were close.
More accurate results were obtained by measuring the amounts of heat of carbon dioxide, nitrogen and urea released by humans. Based on these data, the balance of protein, fat and carbohydrate metabolism was calculated. And here the coincidence turned out to be quite good.
Currently, calorimetric measurements make it possible to draw important conclusions about human life and provide direction for the diagnosis of certain diseases. A thermal imager has recently been created - a device that clearly shows temperature changes in the human body. This method allows you to recognize a variety of ailments associated with inflammatory processes accompanied by an increase in temperature in a given area of the body. Let us present the efficiency of some biological processes
BIOLOGICAL PROCESS | Efficiency % |
Glow of bacteria | |
Muscle contraction | |
Photosynthesis |
1.8. ELECTRICAL PHENOMENA IN THE HUMAN BODY.
One of the most important functions of a living organism is the ability to respond to changes in the environment, called irritability. For example, single-celled protozoa are able to respond to changes in temperature or lighting using a mechanical response (amoeboid movement, movement of cilia and flagella). Irritability is most developed in animals that have specialized cells that form nervous tissue. Nerve cells - neurons are adapted for a quick and specific response to a variety of irritations coming from the external environment and the tissues of the body itself. Reception and transmission of irritations occurs with the help of electrical impulses propagating along certain paths. During embryonic development, a long process, an axon, grows from the body of a nerve cell, forming something like a telegraph wire for transmitting messages (Fig. 9). In an adult, the length of the axon can reach 1–1.5 m with a thickness of about 0.01 mm. Axons are sometimes compared to electrical wires, but in reality the electrical signal travels along them differently than through a wire. While the current travels in a copper wire close to the speed of light, in the axon the impulse travels at speeds of up to 100 m/s. The contents of the axon have a specific electrical resistance that is approximately 100 million times greater than that of a copper wire. In addition, the insulating capacity of the outer membrane of the axon is approximately 1 million. times weaker than the sheath of a good cable. If the propagation of an electrical signal along an axon depended only on electrical conductivity, then the signal introduced into it would attenuate within a few millimeters
The axon sheath separates two aqueous solutions that have almost the same electrical conductivity but different chemical compositions. In the external solution, more than 90% of the charged particles are sodium (Na+) and chlorine (Cl-) ions. In the solution inside the cell, the bulk of the positive ions are potassium ions (K+), and the negative ones are large organic ions. The concentration of sodium ions (Na+) outside the cell is 10 times higher than inside, and the concentration of potassium ions (K+) inside is 30 times higher than outside. When the membrane is in an unexcited state, it is highly permeable to potassium and only slightly permeable to sodium. Due to the large concentration gradient, potassium ions move out of the axon. As a result, a potential difference of about 60 mV arises, and the internal contents of the cell are charged negatively with respect to the external solution. This potential difference is called the resting potential of the nerve cell.
Any change in the permeability of the membrane to one of the ions can lead to a change in potential. This is exactly what happens when an electrical impulse travels along an axon. If you stimulate an axon with a very weak electric current, it will die out after traveling only a few millimeters along the fiber. If you increase the intensity of the electrical signal applied to the membrane of a nerve cell, then, starting from a certain signal level, it no longer fades. The current reduces the resting potential at the point through which it passes, and the resting potential drops to zero; the membrane depolarizes. In response to the decrease in potential, the permeability of the membrane to sodium suddenly increases. This leads to a further reduction in potential. Sodium ions rush from the surrounding fluid into the axon. As a result, a negative potential of about 60 mV is replaced by a positive potential of about 50 mV. This new state signifies the occurrence of an action potential. The axon generates its own impulse, which propagates at a constant speed along its entire length from one end to the other. Immediately after the potential occurs, the effect of membrane permeability for sodium decreases, and for potassium increases, after which the potential in this area returns to the resting level.
BIOLOGICAL ENHANCERS. Information from the external and internal world is perceived by so-called receptors, which are associated with centripetal, or sensitive, neurons. Each receptor perceives only one type of energy: eye receptors perceive light electromagnetic vibrations, ear receptors perceive sound, skin receptors detect mechanical or temperature stimulation. And in the skin their functions are divided: some react only to touch, others to pressure, others to stretching, etc. Temperature receptors are also specialized: some react to cold, others to heat.
As a result of stimulation, nerve impulses arise, the nature of which is the same. A nerve impulse traveling along the auditory nerve is no different in its biophysical nature from a nerve impulse traveling to the brain from a visual, sensory or tactile receptor. The signals are not mixed. They follow all certain paths and end up in certain centers. Not only receptors take part in perception, but also nerves through which excitation goes to the brain, which perceive this excitation. All received energy is converted into a stream of nerve impulses and converted into a form accessible for coding. The sensitivity of the analyzers is amazing. Organisms have a kind of “amplifiers,” i.e., devices that reduce their sensitivity threshold. To make their action clear, let us recall one example. When a hunter pulls the trigger of a weapon, he applies a small amount of force. But the bullet pushes out gases that result in the ignition of gunpowder, and the kinetic energy of the flying bullet becomes significant! Similarly, the threshold of sensitivity in the body decreases. For example, the eye is capable of perceiving several quanta of light! Similar processes of increasing sensitivity occur not only in the visual, but also in other analyzers.
REGISTRATION OF BIOPOTENTIALS. Biopotentials are the differences in electrical potentials that arise in the cells, tissues and organs of a living organism. The biopotentials of individual cells that make up a certain tissue or organism, when summed up, form a resulting potential difference, the change in time of which is characteristic of the tissue or organ. This potential difference can be measured or recorded using specially placed electrodes. The potential difference from the electrodes is applied to an amplifier and then recorded on a moving tape recording device.
Since biopotentials very subtly reflect the functional state of organs and tissues, their registration with subsequent study is a very common technique in physiological studies and in diagnosing diseases. The most common recordings are the potentials of the heart (ECG - electrocardiography), brain (EEG - electroencephalography), as well as peripheral nerve trunks and muscles (EMG - electromyography).
The potentials that arise during the work of the heart are recorded using electrodes placed in certain places on the surface of the body, where a large difference in biopotentials is formed during the work of the heart.
The electrocardiogram is a complex asymmetrical curve. Its frequency is related to the heart rate and is normally within the range of 60 – 80 periods per minute. An electrocardiogram of a healthy person is shown in the figure.
An electroencephalograph device is used to record the biopotentials of the brain. Biopotentials of the brain are removed using electrodes placed at various points on the scalp. Oscillation frequencies depend on the state of the body. The figure shows an electroencephalogram. Certain disorders of the brain cause certain changes in biocurrents. This dependence of the nature of the currents on the state of the body allows scientists to study the processes occurring in the human brain. And not only to study, but sometimes to judge whether he is healthy or sick and what the nature of the disease is.
SOME APPLICATIONS OF BIO-DANCEALS. An important and interesting example of new medical technology is a cardiac stimulator (pacemaker) implanted under the skin. In its simplest form, it is a generator of short-term pulses with a fixed frequency and its own power source, mounted in a housing measuring 5*8 cm, coated with a biologically inert polymer. The mass of the stimulator is 100 g. The stimulator is implanted under the skin in a convenient place, and the wires from it, covered with silicone rubber, are brought to the heart muscle and secured to it using small hooks - clamps that serve as electrodes. The pulse frequency is 60 - 70 per minute, the duration (in accordance with the parameters of electrical excitability of the heart muscle) is about 1 - 3 cm, the current strength in the pulses is 3 - 5 mA.
Recently, science has achieved great success in saving a person who has passed into a state of clinical death - resuscitation. Its results are increasingly being used in ambulance practice and in hospitals. In a state of dying of the body, the electrocardiogram changes in shape, amplitude and intervals between individual cycles. However, as long as the electrical activity of the heart remains, the struggle for the life of the dying person continues.
ELECTRICAL PROPERTIES OF FABRICS. The tissues of living organisms are very heterogeneous in composition. The organic substances that make up the dense parts of tissues are dielectrics. However, liquids contain, in addition to organic colloids, solutions of electrolytes and are therefore relatively good conductors.
The specific electrical conductivity of various tissues of the human body at direct current can be characterized by the approximate data given in the table.
SPECIFIC CONDUCTIVITIES Ohm-1*m-1 |
|
Cerebrospinal fluid | |
Blood serum | |
Internal organs | |
Brain and nerve tissue | |
Adipose tissue | |
Dry skin | |
Bone without periosteum |
Cerebrospinal fluid and blood serum have the highest electrical conductivity; the electrical conductivity of internal organs, as well as brain (nervous), fatty and connective tissues is significantly less. Poor conductors, which should be classified as dielectrics, are the stratum corneum of the skin, tendons, and especially bone tissue without periosteum.
The electrical conductivity of the skin, through which the current passes mainly through the channels of the sweat glands and partly the sebaceous glands, depends on the thickness and condition of its surface layer. Thin and especially moist skin, as well as skin with a damaged outer layer of the epidermis, conducts current well. On the contrary, dry, rough skin is a very poor conductor.
Electric current passes through the human body, irritates and excites living human tissue. The degree of changes that occur depends on the strength of the current and its frequency. A current of 1 mA is considered safe for humans. The passage of an industrial current (frequency 50Hz) 3mA through the human body causes a slight tingling in the fingers touching the conductor. A current of 3–5 mA causes an irritating sensation throughout the entire hand. Currents of 8–10 mA lead to involuntary contraction of the muscles of the hand and forearm. Maximum currents = 13 mA, at which a person is able to independently free himself from contact with the electrodes, are called releasing currents. Involuntary muscle contractions with a current of about 15 mA acquire such force that unclenching the hand becomes impossible (non-releasing current). At currents of 0.1 - 0.2A, random contractions of the heart muscle occur, leading to the death of a person.
Under conditions that weaken the insulating ability of the skin (wet hands, wounds, large contact surfaces), voltages of 100 - 120 V or even less can be fatal. Therefore, in a number of industries, low voltage is used for mass professions. For example, for electrical installations, soldering irons designed for a voltage of 24 V are used. In damp rooms, it is allowed to work at a voltage of no more than 12 V.
1.9. VIBRATIONS IN THE HUMAN BODY.
In a living organism, organs, tissues, and cells work rhythmically. Even the cell membrane allows ions to pass through in a certain rhythm. Rhythm disturbance is a sign of disruption of the body’s vital functions. The rhythm system is multi-tiered. On the lower tier there are cellular and subcellular rhythms. More complex tissue rhythms serve as the basis for the rhythmic activity of organs, and the latter determine the rhythm of the organism as a whole. The inhabitants of planet Earth have been adapting for millions of years to its movement around its axis when day gives way to night. Sleep, wakefulness, eating, the rise and fall of performance are determined by the movement of the Earth. Each organism is also subject to seasonal periodicity, which is determined by the movement of the Earth around the Sun and the inclination of the Earth’s rotation axis to the plane of the Earth’s orbit.
Why do living organisms need “clocks”? For best adaptation to periodic external conditions. An important feature of oscillatory systems is the ability to mutually synchronize. Only thanks to this can living systems be tuned correctly, and from a multitude of weakly coupled oscillatory processes the harmony of a periodic phenomenon arises.
The heart is an example of an oscillatory system in living nature. The heart is one of the most perfect oscillatory systems of this kind. The correct functioning of the heart is determined by the synchronous work of a whole group of muscles that provide variable contraction of the ventricles and atria. The synchronization of this work is “managed” by a special organ, the so-called sinus node, which produces synchronizing electrical voltage pulses at a certain frequency. If the synchronous mode of contraction of the heart muscles is disrupted, then so-called fibrillations may occur - chaotic contractions of individual fibers of the heart muscle, which, if emergency measures are not taken, lead to the death of the body. Urgent measures involve forcibly synchronizing the heart using a special massage or using electrical impulses from a special generator. Currently, a miniature electronic generator of synchronizing pulses is even implanted into the body.
An example of vibrations in the human body is the eardrum of the hearing organ. Air vibrations reaching the human ear cause vibrations of the same frequency in the eardrum. These vibrations are transmitted further through the malleus, incus and stapes.
1.10. ELECTROMAGNETIC RADIATION
IN THE HUMAN BODY.
The role of electromagnetic fields in living nature is extremely diverse: their influence on the life activity of organisms, electromagnetic connections between organisms, as well as EMF as a means of location.
Organisms of a wide variety of species exhibit extremely high sensitivity to EMFs, especially to those that are close to the natural fields of the biosphere: geomagnetic and geoelectric fields, atmospheric fields, and solar flares. Under the influence of EMF, a number of physiological functions are disrupted - heart rhythm, blood pressure, metabolic processes, the emotional state changes, the sense of touch, vision, and perception of sound signals are disrupted.
The occupational hazards of different types of EMF are currently being studied. The question of the possible influence on people of EMFs created by radio and television transmitters, as well as atmospheric radio background, has been studied to a greater extent. Meanwhile, the level of these fields has recently increased sharply.
Observations of electromagnetic interactions within and between organisms are very interesting. Previously unknown electromagnetic oscillations generated by the human heart have recently been discovered; The electromagnetic regulation system of the spine, which is associated with a peculiar distribution of surface potentials, was discovered and studied.
II. RESEARCH PART
2.1. PHYSICAL AND ANTHROPOMETRIC
HUMAN INDICATORS
First, let's look at the Guinness Book of Records and take an interest in people's height, weight and other indicators.
Giants:
1.Robert Pershing Wadlow (USA) had a height of 272 cm, span
arms 288 cm, weight 222.7 kg, shoes – 47 cm, palm length – 32.4 cm.
2. Gabriel Estavao Monyane (Mozambique, born 19944) height
245 cm, weight 189 kg.
Dwarfs:
1. Pauline Masters (Holland) had a height of 59 cm, weight 3.4 kg.
2. Colvin Phillips (USA) had a height of 67 cm at the age of 19, weight with clothes 5.4 kg.
Fat people:
1. Ion Brower Minnoka (USA) had a height of 185 cm. In 1963 he weighed 181 kg, in 1966 - 317 kg, in 1976 - 442 kg, in March 1978 - 625 kg. It took 13 people to turn it on the bed.
2. Heaviest Living – Kent Nicholson. He weighs 407 kg, chest 305 cm, waist – 294 cm, hips – 178 cm, neck – 75 cm.
The human memory is capable of storing as much information as is available in the storage of the largest library.
A. Makedonsky knew each of his 30 thousand soldiers by sight.
Heinrich Schliemann could master a foreign language in 6-8 weeks.
The scientist and physicist Abraham Fedorovich Ioffe used the table of logarithms from memory.
Interesting information about the human body can also be gleaned from the book “Physics in Tables”.
Mechanical parameters | Numerical value |
1. Average human density 2. Average blood speed - in the arteries - in the veins 3. Speed of spread of irritation along nerves 4. Pressure in the artery of an adult's arm - lower (at the beginning of the heart contraction phase) - upper (at the end of the heart contraction phase) 5. Force developed by a beating heart - in the initial phase of contraction - in the final phase of contraction 6. Heart work per day 7. Mass of blood ejected by the heart per day 8. Power developed during fast walking | 1036 kg/m3 0.2 – 0.5 m/s 0.1 – 0.2 m/s 40 – 100 m/s 9.3 kPa (70 mmHg) 120 mmRT 86,400 J 5200 kg 200 W |
Electrical parameters | Numerical value |
1. Specific resistance of body tissues - top layer of dry skin - blood - muscles 2. The dielectric constant - dry skin - blood 3. Human resistance from the end of one arm to the end of the other 4. Current strength through the human body - safe - life-threatening 5. Safe Electrical Voltage - dry room - damp room | 3.3*105 Ohm*m 1.8 Ohm*m 1.5 Ohm*m 15,000 Ohm 0.001 A |
Optical parameters | Numerical value |
| Lens refractive index Optical power - lens - just eyes 3. Intraocular pressure 4. Number of rods in the retina 5. Number of cones in the retina 6. Minimum image size of an object on the retina 7. Duration of retention of visual sensation by the eye 8. The wavelength of light to which the eye is most sensitive 9. Diameter of the eyeball of an adult 10. Pupil diameter - in daylight - in night lighting |
104 kPa (780 mmHg) 130 000 000 7 000 000 0.002 mm 555 nm 24-25 mm 2-3 mm 6-8 mm |
Acoustic parameters | Numerical value |
1. Frequency of sound waves heard by humans | 17 – 20,000 Hz |
Radiation parameters | Numerical value |
1. Permissible radiation dose 2. Radiation dose caused by radiation sickness Lethal dose of radiation | up to 0.25 Gy 1-6 g 6-10 g |
2.2. LABORATORY EXPERIMENT
LABORATORY WORK No. 1
TOPIC: “Determination of human growth indicators.”
PURPOSE: determine height, chest, waist, hips, shoulder, head, wrist, neck, hip.
EQUIPMENT: measuring tape.
PROGRESS
No. | Measurement parameter | L + ΔL |
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163 + 0,5 |
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Inhalation chest circumference | 86 + 0,5 |
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Exhalation chest circumference | 80 + 0,5 |
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Waist circumference | 69 + 0,5 |
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Shoulder circumference | 25,5 + 0,5 |
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Thigh circumference | 85 + 0,5 |
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Shin circumference | 34 + 0,5 |
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Wrist circumference | 15,5 + 0,5 |
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Head circumference | 54 + 0,5 |
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Neck circumference | 35 + 0,5 |
Conclusion: I measured my height and in comparison with the table of Czechoslovak researchers Sramkova, Zelezny and Prokopets it turned out that I have proportional development, but I will never become a tall girl
LABORATORY WORK No. 2
TOPIC: “Determination of the average power developed when running 30 m
squatting and running up stairs.”
EQUIPMENT: scales, ruler, rope with weights, stopwatch.
PROGRESS
a) power when running over a distance of 30 meters
1. Let's measure body mass m.
2. Let's measure the running time t.
3. Let us calculate the average power Nav using the formula Nav = 2mS2 / t3 taking into account the relation S=vav t = vt / 2.
Nav = 2 * 55kg * (30m)2 / (6.19 s)3 = 2583.77W
Let's calculate the error.
Nav depends on m, t and S.
Δm = 0.1 kg Δt = 0.005 s ΔS = 0.5 cm = 0.005 m
ε = Δm / m + 3* Δt / t + 2* ΔS / S = 0.1/55+3*0.005/6.19 + 2*0.005/30 = 0.17
ΔN = Nav * ε = 2583.77 W * 0.17 = 448.34 W
Conclusion: I determined the average power developed when running 30 meters, and it turned out to be equal to
Nav = 2583.77 + 448.34 W
b) average power when squatting
1. Measure the height of your lower back H
2. Measure the height of your body h in the “crouching” position
4. Let's do n squats in time t
5. Calculate the average power using the formula N = n*m*g *(N – 0.5*h) / t
Let's calculate the error.
Nav depends on m, t, h and H.
Δm = 0.1 kg Δt = 0.005 s ΔH = 0.5 cm = 0.005 m Δh = 0.5 cm = 0.005 m
ε = Δm / m + Δt / t + ΔН / Н + Δh/ h = 0.1 / 55 + 0.005 / 10.25 + 0.005 / 1.03 + +0.005 / 1.02 = 0.012
ΔN = Nav * ε = 274.25 W * 0.012 = 3.29 W
Conclusion: I determined the average power developed during a squat, and it turned out to be equal to
Nav = 274.25 + 3.29 W
c) average power when running up stairs
1. Measure the height of the ladder h by lowering a weight on a rope
2. Determine the time t spent climbing the stairs
3. Let's measure the mass of our body m
4. Calculate the average power Nav
Let's calculate the error.
Nav depends on m, t, h.
Δm = 0.1 kg Δt = 0.005 s Δh = 0.5 cm = 0.005 m
ε = Δm / m + Δt / t + Δh/ h = 0.1 / 55 + 0.005 / 3.14+ 0.005 / 5.15 = 0.004
ΔN = Nav * ε = 328.63 W * 0.004 = 1.31 W
Conclusion: I determined the average power developed when running up the stairs, and it turned out to be equal to
Nav = 328.63 + 1.31 W
LABORATORY WORK No. 3
TOPIC: “Arm strength when performing exercises on the horizontal bar.”
EQUIPMENT: scales, water bath, measuring cup.
PROGRESS
1. Let's measure body mass m.
2. Hanging on the bar in the gym with one arm, feel the tension in the arm muscles.
3. Calculate the force of gravity acting on the body using the formula Ft = mg
4. Determine the volume of your body Vt.
5. Let’s find the buoyant force acting on the body from the air using the formula Fa =ρ ggVt, let’s take the air density to be 1.29 kg/m3.
6. Let’s find the strength of our hand using the formula F = F t - F a.
Let's calculate the error.
Ft depends on m and Vt.
Δm = 0.1 kg ΔV= 0.0005 m3
ε = Δm / m + ΔV / V = 0.1 / 55 + 0.0005 / 2.35 = 0.002
ΔF = Ft * ε = 539 N * 0.002 = 1.08 N
Conclusion: I determined the strength of the arm while hanging on the bar and it turned out to be equal to
F = 539 + 1.08 N
LABORATORY WORK No. 4
TOPIC: “Determination of mechanical work during a high jump.”
EQUIPMENT: scales, ruler, bar.
PROGRESS
1. Let's measure body mass m.
2. Measure the height of your lower back H. (Center of gravity at the level of the lower back).
3. Let's measure the height of the bar h that I want to jump over.
4. Let's take the leap
5. Let’s calculate the perfect mechanical work A = mg (h – H).
Let's calculate the error.
A depends on m, H and h.
Δm = 0.1 kg ΔН= 0.005 m Δh= 0.005 m
ε = Δm / m + ΔН / Н + Δh /h = 0.1 / 55 + 0.005 / 1.03 + 0.005 / 1.03 = 0.0113
ΔA = A * ε = 10.78 J * 0.0113 = 0.12 J
Conclusion: I determined the mechanical work during a high jump and it turned out to be equal to
A = 10.78 + 0.12 J
LABORATORY WORK No. 5
TOPIC: “Determination of mechanical work and hand power when climbing a rope.”
EQUIPMENT: scales, ruler, stopwatch, rope.
PROGRESS
1. Let's measure body mass m.
2. In the gym, we will climb the rope without using our legs and note the time of ascent t.
3. Measure the height of the rope h.
4. Let's calculate the perfect mechanical work A = mgh.
5. Calculate the power during lifting N = A / t
Let's calculate the error.
A depends on m and h.
Δm = 0.1 kg Δh= 0.005 m
ε = Δm / m + Δh / h = 0.1 / 55 + 0.005 / 2.60 = 0.004
ΔA = A * ε = 1401.4 J * 0.004 = 5.61 J
N depends on m, t and h.
Δm = 0.1 kg Δh= 0.005 m Δt = 0.005 s
ε = Δm / m + Δh / h + Δt / t = 0.1 / 55 + 0.005 / 2.60 + 0.005 / 9.34 = 0.005
ΔN = N * ε = 150.04 J * 0.005 = 0.75 W
Conclusion: I determined the mechanical work and power when climbing a rope, and they turned out to be equal
A = 1401.4 + 5.51 J N = 150.04 + 0.75 W
LABORATORY WORK No. 6
TOPIC: “Determination of pressure exerted on the floor.”
EQUIPMENT: scales, checkered paper, pencil.
PROGRESS
1. Let's measure body mass m.
2. Trace the sole of your shoes on a piece of paper
3. Count the number of complete cells N1 and the number of incomplete cells N2 and calculate the area of the sole of the shoe using the formula
S = (N 1 + 0.25 * N 2) / 4
4. Calculate the pressure on the floor using the formula P = mg / (2 * S).
Let's calculate the error.
P depends on m and S.
Δm = 0.1 kg ΔS = 0.0001 m 2
ε = Δm / m + ΔS / S = 0.1 / 55 + 0.0001 / 0.02028 = 0.0023
ΔР = Р * ε = 13289 Pa * 0.0023 = 30.56 Pa
Conclusion: I determined the pressure of my body on the floor, and it turned out to be equal
P = 13289 + 30.56 Pa
LABORATORY WORK No. 9
TOPIC: “Determination of the vital capacity of the lungs.”
OBJECTIVE: Experimentally determine the volume of exhaled air
in one cycle.
EQUIPMENT: measuring tape, round inflatable ball.
PROGRESS
1. Inhale air and exhale it as much as possible into an inflatable rubber ball.
2. Measure the circumference of the ball L.
3. Let's repeat the experiment 10 times. We will enter the measurement results into the table.
4. Calculate the volume of air in the ball using the formula
V = π * R 3, where R = L / (2 * π)
General formula V = L 3 / (8 * π2)
Let's calculate the error.
V depends on L.
ε = ΔL / Laver = 0.01 / 0.4154 = 0.024
Δ V = Vav * ε = 0.896 * 0.0024 = 0.022 l
Conclusion: I determined the vital capacity of my lungs, and it turned out to be equal to V = 0.896 + 0.022 l
CONCLUSION
After conducting a number of simple studies, I learned about my body even more. It turned out that I have average anthropometric indicators (height 163 cm, weight 55 kg), my body exerts a pressure of about 13.5 kPa on the floor, the functional test is normal, which indicates that I have no diseases. The vital capacity of my lungs is slightly less than 1 liter. I determined the power I developed when running at a distance of 30 meters, squatting, running up stairs and climbing a rope. It turned out that I develop the most power when running, and the least when climbing a rope. I also determined the mechanical work done during a high jump. It turned out to be surprisingly small, only 10.78 J, since the highest height of the bar that I can jump over is 1 m 5 cm. I also determined the average speed of movement from the house to the school bus parking lot. It was 1.89 m/s or 6.8 km/h.
While working on my essay, I not only examined my body, but also acquired computer skills. I think that both will help me in further studies in my chosen specialty.
For practical calculations and theoretical studies of operator vibration protection systems, dynamic models of the human body are used in the form of analytical relationships (for example, frequency characteristics) or in the form of equivalent mechanical systems (usually with several degrees of freedom).
During experimental research and testing of man-machine systems under extreme conditions, special simulators (anthropomorphic dummies) are used to replace the human tester in dangerous conditions.
Calculated dynamic models, as well as anthropomorphic mannequins, must be equivalent to the human body in the following basic indicators: a) geometric dimensions and shapes, b) distribution of masses of body parts (in particular, the location of the centers of mass of body parts, the values of these masses and moments of inertia), c) types of connections of individual links, d) elastic and damping properties
In Fig. 1, a shows an approximate design diagram of a typical mannequin, and in Fig. 1, b - averaged anthropometric data of the human body.
The average inertial characteristics of individual parts (segments) of the human body are shown in Fig. 2, Mass values are given as a percentage of the total mass of a person; values of moments of inertia relative to the axes passing through the center of mass of the segment; the location of the center of mass is indicated as a percentage of the length of the segment.
The position of the general center of mass depends on the posture adopted by the person (Fig. 3).
The connections between the individual links of the human body (or an equivalent dummy) are kinematic pairs with different degrees of mobility (within limited limits). Idealized diagrams of the connections of the body links are given in Table 1.
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The largest values of the angles of rotation of some parts of the body, due to the mobility of the corresponding joints, are given in Table. 2.
The basic physical and mechanical parameters necessary for constructing models of the human body, characterizing the elastic-damping properties of human tissues, are listed in Table 3 (average values).
Rice. 3. Position of the center of mass of a sitting person’s body
(see scan)
The dependence of stresses on relative strains for biological tissues is nonlinear; in table Figure 4 shows these dependencies obtained for samples of human soft and bone tissue.
The characteristics of the torsional stiffness of the elements of the human skeleton are given in Table. 5 in the form of a torque applied to the end sections of the element, depending on the angle of mutual rotation of the sections.
