Basic provisions of Lamarck's theory. Evolutionary hypothesis

SECTION "Strength of materials"

Basic provisions. Basic hypotheses and assumptions. Types of loads and basic deformations.

Strength of materials- there is a science about the strength and deformation of bodies, elements of machines and structures. strength- called the ability of the material of structures and their elements to resist the action of external forces without collapsing. WITH Opromat considers methods for calculating structural elements for strength, rigidity and stability. R Strength calculations make it possible to determine the dimensions and shapes of a part that can withstand a given load at the lowest cost of material. Under rigidity refers to the ability of a body or structure to resist the formation of deformation. Stiffness calculations ensure that changes in the shape and dimensions of the structure and its elements do not exceed the allowable limits. Under sustainability refers to the ability of a structure to resist forces that try to bring it out of equilibrium. Stability calculations prevent sudden buckling and distortion of part lengths. In practice, in most cases, one has to deal with structures of complex shape, but they can be imagined as consisting of separate simple elements (bars, arrays). The main design material of the sopromat is a bar, that is, a body whose transverse dimensions are small compared to the length. The ability of a material to eliminate deformation after the cessation of external forces is called elasticity. Main hypotheses and assumptions: 1) the hypothesis of the absence of initial internal forces - suppose that if there are no reasons causing deformation of the body (load), then at all its points all its efforts are equal to 0, thus the forces of interaction between the parts and the loaded body are not taken into account. 2) the assumption of one-sidedness of the material, physics - the mechanical properties of the body may not be the same at different points. 3) the assumption of the continuity of the material, the material of any body has a continuous structure and is a continuous medium. 4) the assumption of the isotropy of the material, we assume that the material of the body in all directions has the same properties. A material that has unequal properties in different directions is called anisotropic (wood). 5) the assumption of ideal elasticity, we assume that within certain limits the loading of the material has ideal elasticity, that is, after the load is removed, the deformation completely disappears.

A change in the linear and angular dimensions of a body is called linear and angular deformation, respectively. 1) the assumption of small displacement or the principle of initial dimensions. 2) the assumption of linear deformation of bodies, the displacement of points and sections of an elastic body within certain limits is loaded in proportion to the forces caused by these displacements. 3) the hypothesis of flat sections. Types of loads and basic deformations: Surface loads are concentrated or distributed, depending on the nature of the load, divided into static and dynamic. statistical loads are called numerical values, the direction and place of which remains constant or changes slowly and not significantly. dynamic are called loads characterized by fast adhesion in time of their direction or location. The main types of deformations: 1) tension - chains; 2) compression - columns; 3) shift - seals, dowels. The shear deformation brought to the destruction of the material is called shear. 4) Torsion 5) bending - beams, axles.

Section method. Voltage.

The method of sections is that the body is mentally cut by a plane into 2 parts, any of which is discarded and in return for it, forces acting before the cut are applied to the remaining section, the remaining part is considered as an independent body that is in equilibrium under the action of external and internal forces applied to the section . According to Newton's 3rd law, the internal forces acting in the section of the remaining and discarded parts of the body are equal in absolute value, but opposite, therefore, considering the balance of any of the 2 parts of the dissected body, we got the same value of internal forces. Figure page 8 in lectures.

Types of deformations. Hooke's law in tension and compression.

With different deformations of the cross section of the beam, various internal factors arise:

1) only longitudinal force N occurs in the section, in this case this deformation is tension if the force is directed away from the section. 2) only transverse force Q occurs in the section, in this case this shear deformation. case, this is a torsion deformation. 4) a bending moment M occurs in the section; in this case, this is a pure bending deformation; if both M and Q occur simultaneously in the section, then the bend is transverse.

Hooke's law is valid only within certain load limits. Normal stress is directly proportional to relative elongation or shortening. E - coefficient of proportionality (modulus of longitudinal elasticity) characterizes the rigidity of the material, i.e. the ability to resist elastic deformations of tension or compression.

Stress and longitudinal deformation in tension and compression. Tensile and compressive strength calculations.

As a result of mechanical tests, the limiting stress was established, at which there is a malfunction or destruction of the material of the structural part. To ensure the strength of the part, it is necessary that the stresses arising in them during operation be less than the limiting ones.
safety factor.
;S - called the allowable strength factor. It depends on the properties, quality and homogeneity of the material. For fragile S = 2 - 5, for wood 8 - 12.
allowable voltage.
tensile and compressive strength condition.

Tension or compression is a type of deformation in which only a longitudinal force occurs in any section of the beam. Bars with a straight axis (straight bars) working in tension or compression are called rods. In tension, the hypothesis of flat sections is valid, that is, all the fibers of the beam are elongated by the same amount. During tension and compression in the cross sections of the beam, only normal stresses appear, which are evenly distributed over the section.
the shape of the section does not affect the voltage. In all sections of the beam, the stress is distributed evenly and in the section where a concentrated force is applied to the beam along the axis, the value of the longitudinal force and stress changes abruptly.
relative extension.

Physical basis of strength. Tensile diagram of mild steel.

Graph… page 14 in lectures. You describe: 3 straight lines parallel to each other with a dotted line at an angle of 30 degrees. The triangle is small near the origin. Points tell where what.

they call the maximum stress to which the deformations grow in proportion to the load, that is, Hooke's law is valid. Point A corresponds to another limit, which is called the elastic limit.

The elastic stress is the stress up to which the deformations practically remain elastic.

C-yield stress - the stress at which a noticeable elongation appears in the sample without increasing the load. B - temporary resistance or tensile strength. temporary resistance is called the conditional stress equal to the ratio of the maximum force that the sample can withstand to the initial cross-sectional area, when the temporary resistance is reached, a narrowing is formed on the stretched sample - the neck, that is, the destruction of the sample begins. We are talking about conditional stress, since the stress in the cross section of the neck will be large. M-corresponding to the voltage has arisen. In the smallest cross section at the moment of rupture - the rupture stress.
.

Statistically indeterminate rod systems. Displacement compatibility equation.

Statically indeterminate systems- these are elastic rod systems (structures), in which the number of unknown internal forces and reactions of the supports is greater than the number of static equations possible for this system.

In addition to the equations of statics, to calculate such systems (structures), one has to involve additional conditions that describe the deformation of the elements of this system. They are conditionally called displacement equations or strain compatibility equations (and the solution method itself is sometimes called the strain comparison method).

Degree of static indeterminacy system is the difference between the number of unknowns and the number of independent equilibrium equations that can be compiled for a given system.

The number of additional displacement equations required to reveal the static indeterminacy must be equal to the degree of the static indeterminacy of the system.

Compatibility equations displacements are called canonical equations of the method of forces, since they are written according to a certain law (canon). These equations, the number of which is equal to the number of extra unknowns, together with the equilibrium equations, make it possible to reveal the static indefinability of the system, i.e., to determine the values of extra unknowns.

Formula for shear stresses in torsion. Torsion deformation. Calculations for strength and torsional stiffness.

Torsion is a type of deformation in which only one force factor arises in the cross section of the rod - the torque Mz. Torque, by definition, is equal to the sum of the moments of internal forces about the longitudinal axis of the rod Oz. Normal forces parallel to the Oz axis do not contribute to the torque.

As can be seen from the formula, shifts and shear stresses are proportional to the distances from the axis of the rod. Let us pay attention to the structural analogies of the formulas for the normal stresses of pure bending and shear stresses of torsion. Hypotheses taken in the calculation for torsion:

1) sections that are flat before deformation remain flat after deformation (Bernoulli's hypothesis, the hypothesis of flat sections);

2) all radii of a given section remain straight (do not curve) and rotate through the same angle ϕ, that is, each section rotates about the x axis like a hard thin disk;

3) the distances between the sections do not change during deformation.

In torsion, strength calculations are also divided into design and verification. The calculations are based on the condition of strength where τmax is the maximum shear stress in the bar, determined by the above equations, depending on the shape of the section; [τ] - allowable shear stress, equal to the part of the ultimate stress for the material of the part - tensile strength τv or yield strength τt. The safety factor is set from the same considerations as in tension. For example, for a shaft with a hollow circular cross section, with an outer diameter D and an inner diameter d, we have where α=d/D is the coefficient of the sectional cavity.

The torsional stiffness condition for such a shaft is as follows: where [φo] - permissible relative angle of twist

Statically indeterminate problems in torsion

In torsion, as well as in tension, statically indeterminate problems may occur, for the solution of which the equations of compatibility of displacements must be added to the equations of equilibrium of statics.

It is easy to show that the method for solving these problems in torsion and in tension is the same. Consider, for example, a bar embedded with both ends into absolutely rigid walls (Fig. 7.21). We discard the terminations, replacing their action with the unknown moments M1 and M2. The strain compatibility equation is obtained from the condition that the angle of twist in the right-hand embedment is equal to zero:

Where Ip1=πd14/32, Ip2=πd24/32.

The torques in the beam sections are related by the following equation:

Solving these equations together for unknown moments, we obtain:

The angle of twist of the section C is determined from the equation

Plots of torques and angles of twist are presented in fig. 7.21.

Direct transverse bending of beams. Pure bending of the diagram of internal forces during bending of beams.

Pure bending is a type of deformation in which only a bending moment occurs in any cross section of the beam, the deformation of pure bending will be if 2 pairs of forces equal but opposite in sign are applied to the beam, a plane passing through the axis. Beams, axles, shafts work on bending. We will consider such bars that have at least 1 plane of symmetry and the plane of action of the loads coincides with it, in this case the bending deformation occurs in the plane of deformation of external forces and the bending is called direct. transverse bend- bending, in which, in addition to the internal bending moment, a transverse force also arises in the sections of the rod. For pure bending, the hypothesis of flat sections is valid. The fibers lying on the convex side are stretched, those lying on the concave side are compressed at the boundary. Between them lies the central layer of fibers that only bends without changing its length. With pure bending, normal tensile and compressive stresses arise in the cross sections of the beam, which are unevenly distributed over the section.

The analysis of the above differential dependencies during bending allows us to establish some features (rules) for constructing diagrams of bending moments and shear forces:

A - in areas where there is no distributed load q, plots Q are limited to straight lines parallel to the base, and diagrams M- oblique straight lines;

b - in areas where a distributed load is applied to the beam q, plots Q are limited by oblique straight lines, and diagrams M are quadratic parabolas. In this case, if the diagram M we build “on a stretched fiber”, then the bulge of the pa rabola will be directed in the direction of action q, and the extremum will be located in the section where the diagram Q crosses the baseline;

V - in sections where a concentrated force is applied to the beam on the diagram Q there will be jumps in magnitude and in the direction of the given force, and on the diagram M- kinks, the tip directed in the direction of this force;

G - in sections where a concentrated moment is applied to the beam on the diagram Q there will be no changes, but on the diagram M– jumps by the value of this moment;

e - in areas where Q>0, moment M increases, and in areas where Q M decreases (see figures a-d).

bending hypotheses. Formula for Normal Stresses

There are three such hypotheses for bending:

a - the hypothesis of flat sections (Bernoulli's hypothesis) - the sections are flat before deformation and remain flat after deformation, but only rotate about a certain line, which is called the neutral axis of the beam section. In this case, the beam fibers lying on one side of the neutral axis will be stretched, and on the other, they will be compressed; fibers lying on the neutral axis do not change their length;

b - the hypothesis of the constancy of normal stresses - stresses acting at the same distance y from the neutral axis, constant along the width of the beam;

c – hypothesis about the absence of lateral pressures – neighboring longitudinal fibers do not press on each other.

Maximum normal bending stresses find by the formula: Where W z– axial moment of resistance

In tension and compression, only normal stresses appear in the cross sections of the beam, evenly distributed over the section. The shape of the section does not affect the stress. In all sections of the beam, the stress is distributed evenly and in the section where a concentrated force is applied to the beam along the axis, the value of the longitudinal force and stress changes abruptly. relative extension.

Differential dependencies in bending

Let's establish some relationships between internal forces and external loads in bending, as well as the characteristic features of diagrams Q And M, knowledge of which will facilitate the construction of diagrams and allow you to control their correctness. For convenience of notation, we will denote: M≡M z , Q≡Q y .

On the section of the beam with an arbitrary load, in a place where there are no concentrated forces and moments, we select a small element dx. Since the entire beam is in equilibrium, then the element dx will be in equilibrium under the action of the transverse forces applied to it, bending moments and external loads. Because the Q And M in the general case change along the axis of the beam, then in the sections of the element dx there will be transverse forces Q And Q+dQ, as well as bending moments M And M+dM. From the condition of equilibrium of the selected element, we obtain
The first of the two written equations gives the condition

From the second equation, neglecting the term q· dx·( dx/2) as an infinitesimal quantity of the second order, we find

Considering expressions (10.1) and (10.2) together we can get

Relations (10.1), (10.2) and (10.3) are called differential dependences of D. I. Zhuravsky during bending.

Geometric characteristics of plane sections. (static moment of area. Polar moment of inertia. Axial moment of inertia. Moment of inertia with parallel translation of the axes. Principal axes and principal moments of inertia.

The static moment of the area of a flat figure relative to the axis lying in the same plane is the sum of the products of the areas of elementary areas at a distance from them to this axis, taken over the entire area, static moments relative to the axes. May be greater than zero or less.

The polar moment of inertia of a flat figure relative to the pole lying over the entire area is the sum of the products of the areas of elementary areas by the squares of their distances to the pole.
the polar moment of inertia is always greater than 0.

The moment of inertia of a mechanical system relative to a fixed axis (“axial moment of inertia”) is a physical quantity Ja, equal to the sum of the products of the masses of all n material points of the system and the squares of their distances to the axis: Where:

mi - mass of i-th point,

ri - distance from the i-th point to the axis.

The axial moment of inertia of the body Ja is a measure of the inertia of the body in rotational motion around the axis, just as the mass of the body is a measure of its inertia in translational motion. Where:

dm = ρdV - mass of a small volume element of the body dV,

ρ - density,

r - distance from element dV to axis a.

If the body is homogeneous, that is, its density is the same everywhere, then

The axes with respect to which the centrifugal moment of inertia of the section vanishes are called the main axes, and the main axes passing through the center of gravity of the section are called the main central axes of inertia of the section.

The moments of inertia about the main axes of inertia of the section are called the main moments of inertia of the section and are denoted by I1 and I2, with I1>I2. Usually, speaking of the main moments, they mean axial moments of inertia about the main central axes of inertia.

Let us assume that the u and v axes are principal. Then From here THIS Equation determines the position of the main axes of inertia of the section at a given point relative to the original coordinate axes. When the coordinate axes are rotated, the axial moments of inertia also change. Let us find the position of the axes, relative to which the axial moments of inertia reach extreme values. To do this, we take the first derivative of Iu with respect to α and equate it to zero: hence, if the moments of inertia of the section relative to the principal axes are the same, then all axes passing through the same point of the section are principal and the axial moments of inertia relative to all these axes are the same: Iu = Iv =Iy=Iz. This property is possessed, for example, by square, round, annular sections.

Statically indeterminate beams and frames. Method of forces for disclosure of static indeterminacy of beams and frames.

Such a system is called statically indeterminate if it cannot be calculated using the equations of statics alone, since it has unnecessary connections. To calculate such systems, additional equations are compiled that take into account the deformations of the system.

Statistically indeterminate systems have a number of characteristic features:

statically indeterminate system- this is a construction, the force factors in the elements of which cannot be determined only from the equilibrium equations (static equations).

Static indeterminacy arises when the number of connections imposed on the system is greater than necessary to ensure its equilibrium. At the same time, some of these connections become, as it were, “superfluous”, and the efforts in them become superfluous unknowns. According to the number of extra unknowns, the degree of static indeterminacy of the system is established. Note that the term “extra” connections is conditional, since these connections are necessary to ensure the strength and rigidity of the system, although they are “redundant” from the point of view of its equilibrium.

Frame- a structure consisting of rods of arbitrary configuration and having one or more rigid (non-articulated) nodes. To reveal the static indeterminacy, it is necessary, in addition to the static side of the problem, to analyze the deformations of the system and, in addition to the equilibrium equations, to compose the deformation compatibility equations, from the solution of which the “extra” unknowns are found. In this case, the number of such equations should be equal to the degree of static indeterminacy of the system. force method. Main idea of the method In order to convert a given statically indeterminate system into a statically determinate one, the following technique is used in the method of forces. All "extra" connections imposed on the structure are discarded, and their action is replaced by the corresponding reactions - forces or moments. At the same time, in order to maintain the given conditions of fastening and loading, the reactions of the dropped bonds should have such values at which the displacements in the direction of these reactions would be equal to zero (or given values). Thus, when disclosing static indeterminacy by this method, it is not the deformations that are sought, but the forces corresponding to them - the reactions of the bonds (hence the name "method of forces").

Let's write down the main stages of disclosure of static indeterminacy by the method of forces:

1) we determine the degree of static indefinability of the system, that is, the number of unnecessary unknowns;

2) remove unnecessary connections and thus replace the original statically indeterminate system with a statically determinate one. This new system, freed from unnecessary connections, is called basic Note that the choice of extra connections can be quite arbitrary and depends only on the desire of the calculator, so that for the same initial statically indeterminate system, various versions of the main systems are possible. However, care must be taken to ensure that the main system remains geometrically unchanged - that is, its elements, after removing unnecessary connections, should not be able to move freely in space. 3) compose equations for deformations at the points of application of extra unknowns. Since these deformations are equal to zero in the original system, the indicated equations must also be equated to zero. Then, from the equations obtained, we find the magnitude of the extra unknowns. The main tasks of the strength of materials. Deformations elastic and plastic. Main hypotheses And assumptions. Classification loads And...

Educational program of basic general education of the Municipal Budgetary General Educational Institution

Educational program

... species. Development of evolutionary ideas species. Development of evolutionary ideas. Main provisions ... « hypothesis steady state", " hypothesis panspermia", " hypothesis biochemical evolution. characterize main hypotheses ...

5 Themes of settlement and graphic works 16 > Questions for the test 16 > Examples of tests for knowledge control 17 > V. Thematic plan for studying the discipline 19

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... Main hypotheses And assumptions when rotating the round shaft. Conditions of strength and rigidity. Shear stresses and angular deformations... under the action of variables loads; e) maximum ... and others. kinds control in accordance with Regulation) Number of points, ...

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Be a mistake admitted student, and ... intellectual loads. CHAPTER...two children major species memory - ... waiting main provisions... connections. Hypothesis inconsistencies - position cognitive theory... relationships). Professional deformation personalities - ...

A hypothesis is an argument about a particular phenomenon, which is based on the subjective view of a person who directs his actions in some established direction. If the result is still unknown to a person, then a generalized assumption is created, and checking it allows you to adjust the general direction of the work. This is the scientific concept of a hypothesis. Is it possible to simplify the meaning of this concept?

Explanation in "non-scientific" language

A hypothesis is the ability to predict, predict the results of work, and this is the most important component of virtually every scientific discovery. It helps to calculate future errors and misses and reduce their number significantly. At the same time, a hypothesis born directly during the work can be proved in a partial way. With a known result, the assumption makes no sense, and then hypotheses are not put forward. Here is a simple definition of the concept of a hypothesis. Now we can talk about how it is built, and discuss its most interesting types.

How is a hypothesis born?

Creating an argument in the human head is not an easy thought process. The researcher must be able to create and update the acquired knowledge, and he must also be distinguished by the following qualities:

problematic vision. This is the ability to show the paths of scientific development, to establish its main trends and to link disparate tasks together. Adds a problematic vision with the skills and knowledge already acquired, the intuition and abilities of a person in research.
Alternative character. This trait allows a person to draw the most interesting conclusions, to find something completely new in known facts.
Intuition. This term denotes an unconscious process and is not based on logical reasoning.

What is the essence of the hypothesis?

The hypothesis reflects the objective reality. In this it is similar to different forms of thinking, but it also differs from them. The main specificity of the hypothesis is that it displays the facts in the material world in a hypothetical way, it does not assert categorically and reliably. Because a hypothesis is an assumption.

Everyone knows that when establishing a concept through the nearest genus and difference, it will also be necessary to indicate distinctive features. The closest gender for a hypothesis in the form of any result of activity is the concept of “assumptions”. What is the difference between a hypothesis and conjecture, fantasy, prediction, guessing? The most shocking hypotheses are not based on speculation alone, they all have certain signs. To answer this question, it is necessary to highlight the essential features.

Signs of a hypothesis

If we talk about this concept, then it is worth establishing its characteristic features.

A hypothesis is a special form of development of scientific knowledge. It is hypotheses that allow science to move from individual facts to a specific phenomenon, generalization of knowledge and knowledge of the laws of development of a particular phenomenon.
A hypothesis is based on making assumptions, which is associated with a theoretical explanation of certain phenomena. This concept acts as a separate judgment or a whole line of interrelated judgments, natural phenomena. Judgments are always problematic for researchers, because this concept refers to probabilistic theoretical knowledge. It happens that hypotheses are put forward on the basis of deduction. An example is the shocking hypothesis of K. A. Timiryazev about photosynthesis. It was confirmed, but initially it all started from assumptions in the law of conservation of energy.
A hypothesis is a reasonable assumption that is based on some specific facts. Therefore, a hypothesis cannot be called a chaotic and subconscious process, it is a completely logically harmonious and regular mechanism that allows a person to expand his knowledge to obtain new information - to cognize objective reality. Again, we can recall the shocking hypothesis of N. Copernicus about the new heliocentric system, which revealed the idea that the Earth revolves around the Sun. He outlined all his ideas in the work “On the Rotation of the Celestial Spheres”, all the guesses were based on a real factual base and the inconsistency of the then-current geocentric concept was shown.

These distinguishing features, taken together, will make it possible to distinguish a hypothesis from other types of assumption, as well as to establish its essence. As you can see, a hypothesis is a probabilistic assumption about the causes of a particular phenomenon, the reliability of which cannot now be verified and proven, but this assumption allows us to explain some of the causes of the phenomenon.

It is important to remember that the term "hypothesis" is always used in a double sense. A hypothesis is an assumption that explains some phenomenon. They also speak of a hypothesis as a method of thinking that puts forward some kind of assumption, and then builds the development and proof of this fact.

Hypothesis is often built in the form of an assumption about the cause of past phenomena. An example is our knowledge of the formation of the solar system, the earth's core, the birth of the earth, and so on.

When does a hypothesis cease to exist?

This is possible only in a couple of cases:

The hypothesis receives confirmation and turns into an already reliable fact - it becomes part of a general theory.
The hypothesis is refuted and becomes only false knowledge.

This can happen during hypothesis testing, when the accumulated knowledge is sufficient to establish the truth.

What is included in the structure of a hypothesis?

A hypothesis is built from the following elements:

basis - the accumulation of various facts, statements (substantiated or not);
form - the accumulation of various inferences, which will lead from the foundation of a hypothesis to an assumption;
assumption - conclusions from the facts, statements that describe and justify the hypothesis.

It is worth noting that the hypotheses are always the same in logical structure, but they differ in content and functions.

What can be said about the concept of hypothesis and types?

In the process of evolution of knowledge, hypotheses begin to differ in cognitive qualities, as well as in the object of study. Let's take a closer look at each of these types.

According to the functions in the cognitive process, descriptive and explanatory hypotheses are distinguished:

A descriptive hypothesis is a statement that refers to the properties inherent in the object under study. Usually, the assumption allows you to answer the questions “What is this or that object?” or “What properties does the object have?”. This type of hypothesis can be put forward in order to reveal the composition or structure of an object, reveal its mechanism of action or features of its activity, and determine functional features. Among descriptive hypotheses, there are existential hypotheses that speak of the existence of some object.
An explanatory hypothesis is a statement based on the reasons for the appearance of an object. Such hypotheses allow us to explain why a certain event occurred or what are the reasons for the appearance of an object.

History shows that with the development of knowledge, more and more existential hypotheses appear that tell about the existence of a particular object. Next, descriptive hypotheses appear that tell about the properties of those objects, and in the end, explanatory hypotheses are born that reveal the mechanism and reasons for the appearance of the object. As you can see, there is a gradual complication of the hypothesis in the process of learning something new.

What hypotheses are there for the object of study? Distinguish between public and private.

General hypotheses help substantiate assumptions about regular relationships and empirical regulators. They play the role of a kind of scaffolding in the development of scientific knowledge. Once hypotheses are proven, they become scientific theories and contribute to science.
A private hypothesis is an assumption with justification about the origin and quality of facts, events or phenomena. If there was a single circumstance that caused the appearance of other facts, then knowledge takes the form of hypotheses.
There is also such a type of hypothesis as a working one. This is an assumption put forward at the beginning of the study, which is a conditional assumption and allows you to combine facts and observations into a single whole and give them an initial explanation. The main specificity of the working hypothesis is that it is accepted conditionally or temporarily. It is extremely important for the researcher to systematize the acquired knowledge given at the beginning of the study. After they need to be processed and outline a further route. This is exactly what a working hypothesis is for.

What is a version?

The concept of a scientific hypothesis has already been clarified, but there is another such unusual term - version. What it is? In political, historical or sociological research, as well as in judicial and investigative practice, often when explaining certain facts or their totality, a number of hypotheses are put forward that can explain the facts in different ways. These hypotheses are called versions.

Versions are public and private.

The general version is an assumption that tells about the crime as a whole in the form of a single system of certain circumstances and actions. This version answers not one, but a number of questions.
A private version is an assumption that explains the individual circumstances of a crime. One common version is built from private versions.

What are the requirements for a hypothesis?

The very concept of a hypothesis in the rules of law must meet certain requirements:

it cannot have multiple theses;
the judgment must be framed clearly, logically;
the argument should not include judgments or concepts of an ambiguous nature that cannot yet be clarified by the researcher;
judgment must include a method of solving the problem in order to become part of the study;
when presenting an assumption, it is forbidden to use value judgments, because the hypothesis must be confirmed by facts, after which it will be tested and applied to a wide range;
the hypothesis must correspond to a given topic, subject of research, tasks; all assumptions that are unnaturally tied to the topic are eliminated;
a hypothesis cannot contradict existing theories, but there are exceptions.

How is a hypothesis developed?

Human hypotheses are a thought process. Of course, it is difficult to imagine a general and unified process of constructing a hypothesis: all due to the fact that the conditions for developing an assumption depend on practical activities and on the specifics of a particular problem. However, it is still possible to single out the general boundaries of the stages of the thought process that lead to the emergence of a hypothesis. This:

putting forward a hypothesis;
development;
examination.

Now we need to consider each stage of the emergence of the hypothesis.

Hypothesis

To put forward a hypothesis, you will need to have some facts related to a certain phenomenon, and they must justify the likelihood of the assumption, explain the unknown. Therefore, at first there is a collection of materials, knowledge and facts related to a certain phenomenon, which will be further explained.

Based on the materials, an assumption is made about what the given phenomenon is, or, in other words, a hypothesis is formulated in a narrow sense. The assumption in this case is a kind of judgment that is expressed as a result of processing the collected facts. The facts on which the hypothesis is made can be logically comprehended. This is how the main content of the hypothesis appears. The assumption should answer questions about the essence, the causes of the phenomenon, and so on.

Development and validation

After the hypothesis is put forward, its development begins. If we assume the proposed assumption to be true, then a number of definite consequences should appear. At the same time, logical consequences cannot be identified with the conclusions of the causal chain. Logical consequences are thoughts that explain not only the circumstances of the phenomenon, but also the causes of its occurrence, and so on. Comparison of the facts from the hypothesis with the already established data allows you to confirm or disprove the hypothesis.

This is possible only as a result of testing the hypothesis in practice. A hypothesis is always generated by practice, and only practice can decide whether a hypothesis is true or false. Verification in practice allows you to transform the hypothesis into reliable knowledge about the process (false or true). Therefore, it is not worthwhile to reduce the truth of a hypothesis to a definite and single logical action; when checking in practice, different methods and methods of proof or refutation are used.

Confirmation or refutation of the hypothesis

The work hypothesis is used frequently in the scientific world. This method allows you to confirm or refute certain facts in legal or economic practice through perception. Examples include the discovery of the planet Neptune, the discovery of clean water in Lake Baikal, the establishment of islands in the Arctic Ocean, and so on. All this was once hypotheses, and now - scientifically established facts. The problem is that in some cases it is difficult or impossible to act in practice, and it is not possible to test all assumptions.

For example, now there is a shocking hypothesis that the modern Russian language is more muffled than Old Russian, but the problem is that now it is impossible to hear oral Old Russian speech. It is impossible to check in practice whether the Russian Tsar Ivan the Terrible was tonsured a monk or not.

In cases where prognostic hypotheses are put forward, it is inappropriate to expect their immediate and direct confirmation in practice. Therefore, in the scientific world they use such a logical proof or refutation of hypotheses. Logical proof or refutation proceeds in an indirect way, because phenomena from the past or present time are known, which are inaccessible to sensory perception.

The main ways of logical proof of a hypothesis or its refutation:

inductive way. A more complete confirmation or refutation of the hypothesis and the derivation of certain consequences from it thanks to arguments that include laws and facts.
deductive path. Derivation or refutation of a hypothesis from a number of others, more general, but already proven.
The inclusion of a hypothesis in a system of scientific knowledge, where it is consistent with other facts.

Logical proof or refutation can proceed in direct or indirect form of proof or refutation.

The important role of the hypothesis

Having revealed the problem of the essence, structure of the hypothesis, it is also worth noting its important role in practical and theoretical activities. A hypothesis is a necessary form of development of scientific knowledge; without it, it is impossible to understand something new. It plays an important role in the scientific world, serves as a foundation for the formation of virtually every scientific theory. All significant discoveries in science arose far from ready-made; these were the most shocking hypotheses, which sometimes they did not even want to consider.

Everything always starts small. All of physics has been built on countless shocking hypotheses that have been confirmed or refuted through scientific practice. Therefore, it is worth mentioning some interesting ideas.

Some particles move from the future to the past. Physicists have their own set of rules and prohibitions, which are considered to be canon, but with the advent of tachyons, it would seem that all the norms were shaken. Tachyon is a particle that can violate all the accepted laws of physics at once: its mass is imaginary, and it moves faster than the speed of light. A theory has been put forward that tachyons can move backwards in time. Introduced particle theorist Gerald Feinberg in 1967 and announced that tachyons are a new class of particles. The scientist claimed that this is actually a generalization of antimatter. Feinberg had a lot of like-minded people, and the idea took root for a long time, however, refutations nevertheless appeared. Tachyons have not completely left physics, but still no one has been able to detect them either in space or in accelerators. If the hypothesis were correct, people would be able to communicate with their ancestors.
A drop of water polymer could destroy the oceans. This one of the most shocking hypotheses suggests that water can be transformed into a polymer - a component in which individual molecules become links in a large chain. In this case, the properties of water must change. The hypothesis was put forward by the chemist Nikolai Fedyakin after an experiment with water vapor. The hypothesis for a long time frightened scientists, because it was assumed that one drop of a water polymer could turn all the planet's water into a polymer. However, the refutation of the most shocking hypothesis was not long in coming. The experiment of the scientist was repeated, there was no evidence of the theory.

There were a lot of such most shocking hypotheses at one time, but many of them were not confirmed after a series of scientific experiments, but they were not forgotten. Fantasy and scientific justification - these are the two main components for every scientist.

The most popular among modern scientists is the Oparin-Haldane hypothesis about the origin of life on Earth. According to the hypothesis, life originated from inanimate matter (abiogenically) as a result of complex biochemical reactions.

Regulations

To talk briefly about the hypothesis of the origin of life, it is necessary to highlight three stages in the development of life according to Oparin:

the occurrence of organic compounds;
the formation of polymeric compounds (proteins, lipids, polysaccharides);
the emergence of primitive organisms capable of reproduction.

Rice. 1. Scheme of evolution according to Oparin.

Biogenic, i.e. biological evolution was preceded by chemical evolution, which resulted in the formation of complex substances. Their formation was influenced by the anoxic atmosphere of the Earth, ultraviolet, lightning discharges.

Biopolymers arose from organic substances, which formed into primitive life forms (probionts), gradually separating themselves from the external environment by a membrane. The appearance of nucleic acids in probionts contributed to the transmission of hereditary information and complication of organization. As a result of long-term natural selection, only those organisms remained that were capable of successful reproduction.

Rice. 2. Probionts.

Probionts or procells have not yet been obtained experimentally. Therefore, it is not completely clear how a primitive accumulation of biopolymers could move from an inanimate stay in the broth to reproduction, nutrition and respiration.

Story

The Oparin-Haldane hypothesis has come a long way and has been criticized more than once. The history of the formation of the hypothesis is described in the table.

What have we learned?

From the lesson we learned about the essence of the hypothesis of the origin of life on the Oparin-Haldane Earth. According to the theory, macromolecular substances (proteins, fats, carbohydrates) arose from inanimate matter as a result of complex biochemical reactions under the influence of the external environment. The hypothesis was first tested by Stanley Miller, who recreated the conditions of the Earth before the origin of life. As a result, amino acids and other complex substances were obtained. However, how these substances were reproduced remained unconfirmed.

Topic quiz

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1. What is life?

Answer. Life is a way of being of entities (living organisms) endowed with internal activity, a process of development of bodies of an organic structure with a steady predominance of synthesis processes over decay processes, a special state of matter achieved due to the following properties. Life is a mode of existence of protein bodies and nucleic acids, the essential point of which is the constant exchange of substances with the environment, and with the cessation of this exchange, life also ceases.

2. What hypotheses of the origin of life do you know?

Answer. Various ideas about the origin of life can be grouped into five hypotheses:

1) creationism - Divine creation of the living;

2) spontaneous generation - living organisms arise spontaneously from inanimate matter;

3) the hypothesis of a stationary state - life has always existed;

4) the hypothesis of panspermia - life is brought to our planet from the outside;

5) the hypothesis of biochemical evolution - life arose as a result of processes that obey chemical and physical laws. At present, most scientists support the idea of the abiogenic origin of life in the process of biochemical evolution.

3. What is the basic principle of the scientific method?

Answer. The scientific method is a set of techniques and operations used in the construction of a system of scientific knowledge. The basic principle of the scientific method is to take nothing for granted. Any statement or refutation of something should be checked.

Questions after § 89

1. Why can the notion of the divine origin of life be neither confirmed nor refuted?

Answer. The process of the Divine creation of the world is conceived as having taken place only once and therefore inaccessible for research. Science deals only with those phenomena that can be observed and experimentally studied. Therefore, from a scientific point of view, the hypothesis of the Divine origin of living things can neither be proved nor refuted. The main principle of the scientific method is "take nothing for granted". Therefore, logically there can be no contradiction between the scientific and religious explanation of the origin of life, since these two spheres of thought mutually exclude one another.

2. What are the main provisions of the Oparin-Haldane hypothesis?

Answer. In modern conditions, the emergence of living beings from inanimate nature is impossible. Abiogenic (i.e., without the participation of living organisms) the emergence of living matter was possible only in the conditions of the ancient atmosphere and the absence of living organisms. The composition of the ancient atmosphere included methane, ammonia, carbon dioxide, hydrogen, water vapor and other inorganic compounds. Under the influence of powerful electrical discharges, ultraviolet radiation and high radiation, organic compounds could arise from these substances, which accumulated in the ocean, forming a “primordial soup”. In the "primary broth" of biopolymers formed multimolecular complexes - coacervates. Metal ions, which acted as the first catalysts, entered the coacervate droplets from the external medium. From the huge number of chemical compounds present in the "primordial soup", the most catalytically effective combinations of molecules were selected, which ultimately led to the appearance of enzymes. Lipid molecules lined up on the border between coacervates and the external environment, which led to the formation of a primitive cell membrane. At a certain stage, protein probionts included nucleic acids, creating single complexes, which led to the emergence of such living properties as self-reproduction, preservation of hereditary information and its transmission to subsequent generations. Probionts, whose metabolism was combined with the ability to self-reproduce, can already be considered as primitive procells, the further development of which took place according to the laws of the evolution of living matter.

3. What experimental evidence can be given in favor of this hypothesis?

Answer. In 1953, this hypothesis of A. I. Oparin was experimentally confirmed by the experiments of the American scientist S. Miller. In the installation he created, the conditions that presumably existed in the Earth's primary atmosphere were simulated. As a result of the experiments, amino acids were obtained. Similar experiments were repeated many times in various laboratories and made it possible to prove the fundamental possibility of synthesizing practically all monomers of the main biopolymers under such conditions. Subsequently, it was found that, under certain conditions, it is possible to synthesize more complex organic biopolymers from monomers: polypeptides, polynucleotides, polysaccharides, and lipids.

4. What is the difference between the hypothesis of A. I. Oparin and the hypothesis of J. Haldane?

Answer. J. Haldane also put forward the hypothesis of the abiogenic origin of life, but, unlike A. I. Oparin, he gave priority not to proteins - coacervate systems capable of metabolism, but to nucleic acids, that is, macromolecular systems capable of self-reproduction.

5. What arguments do the opponents give when criticizing the Oparin-Haldane hypothesis?

Answer. The Oparin-Haldane hypothesis also has a weak side, which is pointed out by its opponents. Within the framework of this hypothesis, it is not possible to explain the main problem: how did the qualitative leap from inanimate to living occur. Indeed, for the self-reproduction of nucleic acids, enzyme proteins are needed, and for the synthesis of proteins, nucleic acids.

Give possible arguments "for" and "against" the hypothesis of panspermia.

Answer. Arguments for:

Life at the level of prokaryotes appeared on Earth almost immediately after its formation, although the distance (in terms of the difference in the level of complexity of organization) between prokaryotes and mammals is comparable to the distance from the primordial soup to the paryotes;

In the case of the origin of life on any planet of our galaxy, it, as shown, for example, by A.D. Panov’s estimates, can “infect” the entire galaxy over a period of only a few hundred million years;

Findings in some meteorites of artifacts that can be interpreted as the result of the activity of microorganisms (even before the meteorite hit the Earth).

The panspermia hypothesis (life is brought to our planet from the outside) does not answer the main question of how life arose, but transfers this problem to some other place in the Universe;

Complete radio silence of the Universe;

Since it turned out that our entire Universe is only 13 billion years old (that is, our entire Universe is only 3 times older (!) Of planet Earth), then there is very little time left for the origin of life somewhere far away ... The nearest star to us, a-centauri, is 4 sv. of the year. A modern fighter (4 speeds of sound) will fly to this star ~ 800.000 years.

Ch. Darwin wrote in 1871: “But now ... in some warm reservoir containing all the necessary ammonium and phosphorus salts and accessible to light, heat, electricity, etc., a protein was chemically formed, capable of further , increasingly complex transformations, then this substance would immediately be destroyed or absorbed, which was impossible in the period before the emergence of living beings.

Confirm or refute this statement of Charles Darwin.

Answer. The process of the emergence of living organisms from simple organic compounds was extremely long. In order for life to originate on Earth, it took an evolutionary process that lasted for many millions of years, during which complex molecular structures, primarily nucleic acids and proteins, were selected for stability, for the ability to reproduce their own kind.

If now on Earth somewhere in areas of intense volcanic activity quite complex organic compounds can arise, then the probability of any prolonged existence of these compounds is negligible. The possibility of the re-emergence of life on Earth is excluded. Now living beings appear only through reproduction.

1. In modern conditions, the emergence of living beings from inanimate nature is impossible. Abiogenic (i.e., without the participation of living organisms) the emergence of living matter was possible only in the conditions of the ancient atmosphere and the absence of living organisms. 2. The composition of the ancient atmosphere included methane, ammonia, carbon dioxide, hydrogen, water vapor and other inorganic compounds. Under the influence of powerful electrical discharges, ultraviolet radiation and high radiation, organic compounds could arise from these substances, which accumulated in the ocean, forming a “primordial soup”. 3. In the "primary broth" of biopolymers formed multimolecular complexes - coacervates. Metal ions, which acted as the first catalysts, entered the coacervate droplets from the external medium. From the huge number of chemical compounds present in the "primordial soup", the most catalytically effective combinations of molecules were selected, which ultimately led to the appearance of enzymes. Lipid molecules lined up on the border between coacervates and the external environment, which led to the formation of a primitive cell membrane. 4. At a certain stage, protein probionts included nucleic acids, creating single complexes, which led to the emergence of such living properties as self-reproduction, preservation of hereditary information and its transmission to subsequent generations. Probionts, whose metabolism was combined with the ability to self-reproduce, can already be considered as primitive procells, the further development of which took place according to the laws of the evolution of living matter.

*Year*	*Scientist*	*Main events*
	Soviet biologist Alexander Ivanovich Oparin	The main provisions of Oparin's hypothesis were first formulated in his book "The Origin of Life". Oparin suggested that biopolymers (high molecular weight compounds) dissolved in water, under the influence of external factors, can form coacervate drops or coacervates. These are organic substances gathered together, which are conditionally separated from the external environment and begin to maintain metabolism with it. The process of coacervation - separation of the solution with the formation of coacervates - is the previous stage of coagulation, i.e. clumping of small particles. It was as a result of these processes that amino acids appeared from the "primary broth" (Oparin's term) - the basis of living organisms.
	British biologist John Haldane	Regardless of Oparin, he began to develop similar views on the problem of the origin of life. Unlike Oparin, Haldane assumed that macromolecular substances capable of reproduction were formed instead of coacervates. Haldane believed that the first such substances were not proteins, but nucleic acids.
	American chemist Stanley Miller	As a student, he recreated an artificial environment for obtaining amino acids from inanimate matter (chemicals). The Miller-Urey experiment simulated Earth conditions in interconnected flasks. The flasks were filled with a mixture of gases (ammonia, hydrogen, carbon monoxide), similar in composition to the Earth's early atmosphere. In one part of the system there was constantly boiling water, the vapors of which were subjected to electrical discharges (imitation of lightning). Cooling, the steam accumulated in the form of condensate in the lower tube. After a week of continuous experiment, amino acids, sugars, lipids were found in the flask
	British biologist Richard Dawkins	In his book The Selfish Gene, he suggested that not coacervate droplets were formed in the primordial soup, but molecules capable of reproduction. It was enough for one molecule to arise for its copies to fill the ocean