Weathering itself does not lead to the formation of relief forms, but only turns hard rocks into loose ones and prepares the material for movement. The result of this movement is various forms of relief.
Effect of gravity
Under the influence of gravity, destroyed rocks move on the surface of the Earth from elevated areas to lower ones. Blocks of stone, crushed stone, and sand often rush down steep mountain slopes, causing landslides and screes.
Under the influence of gravity there are landslides and mudflows. They carry huge masses of rocks. Landslides are the sliding of rock masses down a slope. They form along the banks of reservoirs, on the slopes of hills and mountains after heavy rains or melting snow. The upper loose layer of rocks becomes heavier when saturated with water and slides down the lower, water-impervious layer. Heavy rains and rapid snow melting also cause mudflows in the mountains. They move down the slope with destructive force, demolishing everything in their path. Landslides and mudflows lead to accidents and loss of life.
Activity of flowing waters
The most important transformer of relief is moving water, which performs great destructive and creative work. Rivers cut wide river valleys on the plains and deep canyons and gorges in the mountains. Small water flows create gully-gully relief on the plains.
Flowing bottoms not only create depressions on the surface, but also capture rock fragments, transport them and deposit them in depressions or their own valleys. This is how flat plains are formed from river sediments along rivers
Karst
In those areas where easily soluble rocks (limestone, gypsum, chalk, rock salt) lie close to the earth's surface, amazing natural phenomena are observed. Rivers and streams, dissolving rocks, disappear from the surface and rush deep into the bowels of the earth. Phenomena associated with the dissolution of surface rocks are called karst. The dissolution of rocks leads to the formation of karst landforms: caves, abysses, mines, funnels, sometimes filled with water. Beautiful stalactites (multi-meter calcareous “icicles”) and stalagmites (“columns” of limestone growths) form bizarre sculptures in the caves.
Wind activity
In open treeless spaces, the wind moves giant accumulations of sand or clay particles, creating aeolian landforms (Aeolus is the patron god of the wind in ancient Greek mythology). Most of the sandy ones are covered with dunes and sandy hills. Sometimes they reach a height of 100 meters. From above the dune has the shape of a sickle.
Moving at high speed, particles of sand and crushed stone process stone blocks like sandpaper. This process goes faster at the surface of the earth, where there are more grains of sand.
As a result of wind activity, dense deposits of dust particles can accumulate.
Such homogeneous, porous, grayish-yellow rocks are called loess.
Glacier activity
Human activity
Humans play a major role in changing the relief. The plains are especially strongly changed by its activities. People have been settling on the plains for a long time; they build houses and roads, fill up ravines, and construct embankments. Man changes the relief during mining: huge quarries are dug, heaps of heaps are piled up - dumps of waste rock.
The scale of human activity can be comparable to natural processes. For example, rivers carve out their valleys, carrying out rocks, and humans build canals of comparable size.
Landforms created by humans are called anthropogenic. Anthropogenic changes in relief occur with the help of modern technology and at a fairly rapid pace.
Moving water and wind perform enormous destructive work, which is called (from the Latin word erosio, corroding). Land erosion is a natural process. However, it intensifies as a result of human economic activity: plowing slopes, deforestation, excessive grazing, and building roads. In the last hundred years alone, a third of all the world's cultivated land has been eroded. These processes reached their greatest extent in large agricultural regions of Russia, China and the USA.
Formation of the Earth's relief
Features of the Earth's relief
EXTERNAL AND INTERNAL FORCES. In mechanics, external forces in relation to a given system of material points (i.e., such a set of material points in which the movement of each point depends on the positions or movements of all other points) are those forces that represent the action of other bodies (others) on this system systems of material points), not included by us in the composition of this system. Internal forces are the forces of interaction between individual material points of a given system. The division of forces into external and internal is completely conditional: when the given composition of the system changes, some forces that were previously external can become internal, and vice versa. So, for example, when considering the movement of a system consisting of the earth and its moon satellite, the interaction forces between these bodies will be internal forces for this system, and the gravitational forces of the sun, the remaining planets, their satellites and all the stars will be external forces in relation to the specified system . But if we change the composition of the system and consider the movement of the sun and all the planets as the movement of one general system, then the external forces will only be the forces of attraction exerted by the stars; nevertheless, the forces of interaction between the planets, their satellites and the sun become internal forces for this system.
In the same way, if during the movement of a steam locomotive we single out the piston of the steam cylinder as a separate system of material points subject to our consideration, then the steam pressure on the piston in relation to it will be an external force, and the same steam pressure will be one of the internal forces if we consider the movement the entire locomotive as a whole; in this case, external forces in relation to the entire locomotive, taken as one system, will be: friction between the rails and wheels of the locomotive, gravity of the locomotive, reaction of the rails and air resistance; internal forces will be all the forces of interaction between parts of a steam locomotive, for example, the forces of interaction between steam and the piston of a cylinder, between the slider and its parallels, between the connecting rod and the crank pin, etc. As we see, there is essentially no difference between external and internal forces, the relative difference between them is determined only depending on which bodies we include in the system under consideration and which we consider not included in the system. However, the indicated relative difference in forces is very significant when studying the motion of a given system; according to Newton’s third law (on the equality of action and reaction), the internal forces of interaction between each two material points of the system are equal in magnitude and directed along the same straight line in opposite directions; thanks to this, when resolving various questions about the motion of a system of material points, it is possible to exclude all internal forces from the equations of motion of the system and thereby make possible the very study of the motion of the entire system. This method of eliminating internal, in most cases unknown, coupling forces is essential in deriving various laws of mechanics of a system.
External force is a measure of the interaction between bodies. In problems of strength of materials, external forces are always considered given. External forces also include support reactions(connections).
External forces are divided into volumetric And superficial. Volume forces applied to every particle of the body throughout its entire volume. Examples of body forces are weight forces and inertia forces. Often a simple law of changes in these forces over volume is given. Volume forces are determined by their intensity, as the limit of the ratio of the resultant forces in the elementary volume under consideration to the value of this volume tending to zero: \lim_(\Delta V\to0)(\Delta F \over \Delta V) and are measured in N/m 3 .
Surface forces are divided into concentrated And distributed.
Focused The forces applied to a small surface, the dimensions of which are small compared to the dimensions of the body, are considered. However, when calculating stresses near the zone of application of force, the load should be considered distributed. Concentrated loads include not only concentrated forces, but also pairs of forces, an example of which is the load created by a wrench when tightening a nut. Concentrated effort is measured in kN.
Distributed Loads are distributed along the length and area. Distributed loads include the pressure of a liquid, gas or other body. Distributed forces are usually measured in kN/m(distributed along the length) and kN/m 2(distributed by area).
All external loads can be divided into static And dynamic.
Static loads are considered, during the application of which the resulting inertia forces are small and can be neglected.
If the inertia forces are large (for example, an earthquake), the loads are considered dynamic. Examples of such loads can also include suddenly applied loads, drums And re-variables.
Suddenly applied loads are transferred to the construction site immediately
its full value (for example, the pressure of the wheels of a locomotive entering a bridge).
Shock loads occur when the speed of contacting structural elements quickly changes, for example, when the head of a pile driver hits a pile while driving it.
Re-variables loads act on structural elements, repeating themselves a significant number of times. These are, for example, repeated steam pressures that alternately stretch and compress the piston rod and connecting rod of a steam engine. In many cases, the load is a combination of several types of dynamic influences.
Inner forces
As a result of the action of external forces in the body, internal forces.
Inner strength- interaction forces between parts of one body arising under the influence of external forces.
Internal forces are self-balanced, so they are not visible and do not affect the balance of the body. Internal forces are determined by the section method.
External loads lead to the following types of stress-strain state:
- Bend
- Torsion
It is necessary to know the point of application and direction of each force. It is important to be able to determine which forces act on the body and in what direction. Force is denoted as , measured in Newtons. In order to distinguish between forces, they are designated as follows
Below are the main forces operating in nature. It is impossible to invent forces that do not exist when solving problems!
There are many forces in nature. Here we consider the forces that are considered in the school physics course when studying dynamics. Other forces are also mentioned, which will be discussed in other sections.
Gravity
Every body on the planet is affected by Earth's gravity. The force with which the Earth attracts each body is determined by the formula
The point of application is at the center of gravity of the body. Gravity always directed vertically downwards.
Friction force
Let's get acquainted with the force of friction. This force occurs when bodies move and two surfaces come into contact. The force occurs because surfaces, when viewed under a microscope, are not as smooth as they appear. The friction force is determined by the formula:
The force is applied at the point of contact of two surfaces. Directed in the direction opposite to movement.
Ground reaction force
Let's imagine a very heavy object lying on a table. The table bends under the weight of the object. But according to Newton's third law, the table acts on the object with exactly the same force as the object on the table. The force is directed opposite to the force with which the object presses on the table. That is, up. This force is called the ground reaction. The name of the force "speaks" support reacts. This force occurs whenever there is an impact on the support. The nature of its occurrence at the molecular level. The object seemed to deform the usual position and connections of the molecules (inside the table), they, in turn, strive to return to their original state, “resist.”
Absolutely any body, even a very light one (for example, a pencil lying on a table), deforms the support at the micro level. Therefore, a ground reaction occurs.
There is no special formula for finding this force. It is denoted by the letter , but this force is simply a separate type of elasticity force, so it can also be denoted as
The force is applied at the point of contact of the object with the support. Directed perpendicular to the support.
Since the body is represented as a material point, force can be represented from the center
Elastic force
This force arises as a result of deformation (change in the initial state of the substance). For example, when we stretch a spring, we increase the distance between the molecules of the spring material. When we compress a spring, we decrease it. When we twist or shift. In all these examples, a force arises that prevents deformation - the elastic force.
Hooke's law
The elastic force is directed opposite to the deformation.
Since the body is represented as a material point, force can be represented from the center
When connecting springs in series, for example, the stiffness is calculated using the formula
When connected in parallel, the stiffness
Sample stiffness. Young's modulus.
Young's modulus characterizes the elastic properties of a substance. This is a constant value that depends only on the material and its physical state. Characterizes the ability of a material to resist tensile or compressive deformation. The value of Young's modulus is tabular.
Read more about properties of solids.
Body weight
Body weight is the force with which an object acts on a support. You say, this is the force of gravity! The confusion occurs in the following: indeed, often the weight of a body is equal to the force of gravity, but these forces are completely different. Gravity is a force that arises as a result of interaction with the Earth. Weight is the result of interaction with support. The force of gravity is applied at the center of gravity of the object, while weight is the force that is applied to the support (not to the object)!
There is no formula for determining weight. This force is designated by the letter.
The support reaction force or elastic force arises in response to the impact of an object on the suspension or support, therefore the weight of the body is always numerically the same as the elastic force, but has the opposite direction.
The support reaction force and weight are forces of the same nature; according to Newton’s 3rd law, they are equal and oppositely directed. Weight is a force that acts on the support, not on the body. The force of gravity acts on the body.
Body weight may not be equal to gravity. It may be more or less, or it may be that the weight is zero. This condition is called weightlessness. Weightlessness is a state when an object does not interact with a support, for example, the state of flight: there is gravity, but the weight is zero!
It is possible to determine the direction of acceleration if you determine where the resultant force is directed
Please note that weight is force, measured in Newtons. How to correctly answer the question: “How much do you weigh”? We answer 50 kg, not naming our weight, but our mass! In this example, our weight is equal to gravity, that is, approximately 500N!
Overload- ratio of weight to gravity
Archimedes' force
Force arises as a result of the interaction of a body with a liquid (gas), when it is immersed in a liquid (or gas). This force pushes the body out of the water (gas). Therefore, it is directed vertically upward (pushes). Determined by the formula:
In the air we neglect the power of Archimedes.
If the Archimedes force is equal to the force of gravity, the body floats. If the Archimedes force is greater, then it rises to the surface of the liquid, if less, it sinks.
Electrical forces
There are forces of electrical origin. Occurs in the presence of an electrical charge. These forces, such as the Coulomb force, Ampere force, Lorentz force, are discussed in detail in the section Electricity.
Schematic designation of forces acting on a body
Often a body is modeled as a material point. Therefore, in diagrams, various points of application are transferred to one point - to the center, and the body is depicted schematically as a circle or rectangle.
In order to correctly designate forces, it is necessary to list all the bodies with which the body under study interacts. Determine what happens as a result of interaction with each: friction, deformation, attraction, or maybe repulsion. Determine the type of force and correctly indicate the direction. Attention! The amount of forces will coincide with the number of bodies with which the interaction occurs.
The main thing to remember
1) Forces and their nature;
2) Direction of forces;
3) Be able to identify the acting forces
There are external (dry) and internal (viscous) friction. External friction occurs between contacting solid surfaces, internal friction occurs between layers of liquid or gas during their relative motion. There are three types of external friction: static friction, sliding friction and rolling friction.
Rolling friction is determined by the formula
The resistance force occurs when a body moves in a liquid or gas. The magnitude of the resistance force depends on the size and shape of the body, the speed of its movement and the properties of the liquid or gas. At low speeds of movement, the drag force is proportional to the speed of the body
At high speeds it is proportional to the square of the speed
Let's consider the mutual attraction of an object and the Earth. Between them, according to the law of gravity, a force arises 
Now let's compare the law of gravity and the force of gravity 
The magnitude of the acceleration due to gravity depends on the mass of the Earth and its radius! Thus, it is possible to calculate with what acceleration objects on the Moon or on any other planet will fall, using the mass and radius of that planet.
The distance from the center of the Earth to the poles is less than to the equator. Therefore, the acceleration of gravity at the equator is slightly less than at the poles. At the same time, it should be noted that the main reason for the dependence of the acceleration of gravity on the latitude of the area is the fact of the Earth’s rotation around its axis.
As we move away from the Earth's surface, the force of gravity and the acceleration of gravity change in inverse proportion to the square of the distance to the center of the Earth.
Dynamic anatomy
ANALYSIS OF POSITIONS AND MOVEMENTS OF THE HUMAN BODY.
The main provisions of this theoretical course were developed by P.F. Lesgaft and was called “Course on the Theory of Bodily Movements”. This course included an analysis of the general laws of human structure, joint movement, and the position of the human body in space during movement.
Analysis of body positions in space involved the study of human movements in a certain sequence:
- Morphology of movement or position- was based on a purely visual familiarization with the pose, the exercise that was supposed to be performed. At the same time, the position in space of the body and its individual parts - the head, torso, and limbs - was examined in detail.
- Mechanics of body positions– at the same time, the exercise proposed for implementation was considered from the point of view of the laws of mechanics. And this presupposed mandatory familiarization with the forces that have an effect on the human body.
Any movement, exercise, or position of the body is carried out through the interaction of forces that act on the human body. These forces are divided into external and internal.
EXTERNAL FORCES– forces acting on a person from the outside, during his interaction with external bodies (earth, gymnastic equipment, any objects).
1. GRAVITY is the force with which a body is attracted to the ground. It is equal to the weight or mass of the body, applied to its center and directed vertically downward. The point of application of this force is the general center of gravity of the body - GCT. GCT consists of the centers of gravity of individual body segments.
When the body moves downward gravity is the driving force, those. helps movement;
When driving up– slows down movement (interferes);
When driving along horizontal– has a neutral effect.
2. GROUP REACTION FORCE is the force with which the support area acts on the body.
Moreover, if the body retains vertical position, then the support reaction force is equal to the force of gravity and directed opposite to it, i.e. . up.
When walking, running, or standing long jumps, the reaction force of the support will be directed at an angle to the area of support and, according to the rule of parallelogram of forces, can be decomposed into vertical and horizontal components.
A. VERTICAL COMPONENT OF THE SUPPORT REACTION FORCE– directed upward, opposite to gravity (its mirror image).
B. HORIZONTAL COMPONENT (RESISTS FRICTION FORCE)– directed opposite to the direction of movement. Without friction, movement is impossible. Sometimes this strength is artificially increased - tartan coverings on treadmills.
3. POWER OF RESISTANCE TO THE EXTERNAL ENVIRONMENT- this force can either inhibit movement or promote it.
The braking influence of the environment can be reduced by adopting the most favorable (streamlined) body shape, and the drag force of the environment can be increased by increasing the repulsion surface (for swimmers - fins, for rowers - an oar blade).
4. FORCE OF INERTIA – force that occurs when a body moves with acceleration. Rational use of inertial force allows you to save muscle energy. This power may be centripetal, i.e. directed towards the center of rotation and centrifugal– directed from the center of rotation. These forces are opposite in direction. If they are equal, then the body remains at rest; if not, then the body moves towards the larger of them. For a runner, the force of the tailwind is the driving force, i.e. helps the movement, and the force of the headwind acts as a brake.