Presentation is friction. Friction force. friction is the interaction of the surfaces of contacting bodies, preventing their relative movement. friction is the interaction of surfaces. Physics presentation friction force

The friction force is the force that occurs when one body moves on the surface of another and prevents their relative movement. The friction force is the force that occurs when one body moves on the surface of another and prevents their relative movement. Ftr

Causes of friction forces Roughness of the surfaces of contacting bodies (even smooth surfaces have microscopic irregularities and, when sliding, engage with each other and thereby interfere with movement.) Roughness of the surfaces of contacting bodies (even smooth surfaces have microscopic irregularities and, when sliding, engage with each other and thereby hindering movement.)

Force of static friction Why is it not possible to immediately move a heavy box or cupboard? Why can't you immediately move a heavy box or cabinet? Force must be applied to move from the support. This force balances the static friction force. Force must be applied to move from the support. This force balances the static friction force.

Harmful friction Many moving parts of various mechanisms heat up and wear out. Many moving parts of various mechanisms heat up and wear out. The soles of shoes and the tires of car wheels wear out. The soles of shoes and the tires of car wheels wear out.

Ways to reduce friction Treatment of rubbing surfaces to a smooth state. Processing of rubbing surfaces to a smooth state. Replacement of sliding friction by rolling friction. Replacement of sliding friction by rolling friction. Use of lubricant. Use of lubricant.

Friction in nature Many plants and animals have various organs that serve for grasping (the antennae of plants, the elephant's trunk, the tenacious tails of climbing animals). All of them have a rough surface to increase the friction force. Many plants and animals have various organs that serve for grasping (the antennae of plants, the elephant's trunk, the tenacious tails of climbing animals). All of them have a rough surface to increase the friction force. 1. What are the forces of friction? a) Sliding friction. c) static friction. b) Rolling friction. d) All named species. 2. In what cases presented here does the rolling friction force occur? a) 1 and 2. c) 2 and 3. b) 3 and 4. d) 1 and 4. 3. Which of the bodies shown in the figure experience sliding friction? a) 1 and 2. c) 2 and 3. b) 3 and 4. d) 1 and What kind of friction of bodies causes the least friction force? a) Rolling friction. b) In the case of sliding friction. c) During static friction. d) For all types of friction, the forces are the same. 5. How can friction be reduced? a) Lubricate the surfaces of contacting bodies. b) Press the bodies to each other. c) Increase the roughness. d) Polish surfaces. Test
Homework Explain these sayings about friction: If you don't grease, you won't ride. If you don't put it on, you won't go. Things went like clockwork. Things went like clockwork. You can't hold an eel in your hands. You can't hold an eel in your hands. What is round rolls easily. What is round rolls easily. Skis glide according to the weather. Skis glide according to the weather.

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Friction force

MOU "Secondary school No. 24 with in-depth study of subjects" city of Naberezhnye Chelny Republic of Tatarstan

Prepared by: physics teacher Mingazova Maysara Valeevna

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Objectives: to find out what role the friction force plays in our life, how a person received knowledge about this phenomenon, what is its nature.

Tasks: To trace the historical experience of mankind in the use and application of this phenomenon; Find out the nature of the phenomenon of friction, the laws of friction; Conduct experiments confirming the laws and dependencies of the friction force; Think over and create demonstration experiments proving the dependence of the friction force on the force of normal pressure, on the properties of contacting surfaces, on the speed of the relative motion of bodies.

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Let us find out what role the phenomenon of friction or its absence plays in our life; Let's answer the question: "What do we know about this phenomenon?"

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The force of friction in nature

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Is friction good or bad?

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We studied proverbs, sayings, fairy tales, in which the force of friction, rolling, rest, sliding is manifested, we studied human experience in the application of friction, ways to deal with friction.

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There will be no snow, there will be no trace. The quieter you go, the further you'll get. A quiet cart will be on the mountain. Difficult to swim against the water. You love to ride, love to carry sleds. Patience and work will grind everything.

Proverbs and sayings:

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"Kolobok" - rolling friction. (the gingerbread man lay down, lay down, took it and rolled - from the window to the bench, from the bench to the floor ....) "Turnip" - the friction of peace. "Bear Hill" - sliding friction.

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Friction is a phenomenon that has accompanied us since childhood, literally at every step, and therefore has become so familiar and so imperceptible. Friction is not only a brake on movement. This is also the main reason for the wear and tear of technical devices, a problem that man also faced at the very dawn of civilization.

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1. The introduction between the rubbing surfaces of a lubricant (for example, some kind of oil). 2. Use of ball and roller bearings. 3. Air cushion application.

Ways to reduce friction:

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The first rolling bearing made of metal was located in the support of a windmill built in 1780 in England in Sprowston.

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Bearing of the technical revolution period from 1500 to 1850

Machine tool bearings with split adjustable bearing blocks

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What do you know about friction? How do you feel about ice, slippery sidewalk roads? The majority of respondents could not give a definite answer to the first question, because did not see the connection between friction and everyday experience. To the second question, children and schoolchildren of the middle classes said that they liked the ice, they could skate; and older people already understand what the danger of this phenomenon is.

We conducted a small sociological survey of a group of residents who were asked the following questions:

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We have studied the nature of friction forces; Investigated the factors on which friction depends; Considered the types of friction;

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Friction forces

Quiescent Sliding Rolling

Fcontrol = Ftr Ftr V

On contact Along the surface Forgiving movement

electromagnetic

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The phenomenon of the interaction of two bodies in contact, which is expressed in the obstruction of their mutual movement. Nature is electromagnetic interaction. Types: external (rest, sliding, rolling), internal (layers of gas or liquid), resistance (movement of a body relative to gas or liquid)

Friction force Ftr as a characteristic of the action of the surface on the body. The nature of the friction force: a) depends on the material of the body and surface, lubrication, the value of N; b) does not depend on S of the surface; c) Fmax of rest is greater than Fslip; d) Frolling is less than Fsliding; Friction force law (for the case of independence of speed) Ftr=N. The coefficient of friction characterizes the material, the degree of surface treatment; does not depend on N.

Friction reduction: Lubrication, surface treatment, material selection, rolling and plain bearings. Friction increase: sand on the road with ice, chains on wheels, special tires, tread on boots, etc. Calculation of the movement of bodies. Calculation of deformations.

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Friction of rest

Ftr. rest = - F (Ftr. n)max = µN Friction of rest - driving force, "adhesive weight".

rolling friction

Nature… Ftr. quality F tr. sliding Wheel! Bearings! Increase: sand, mittens, nails, screws, spikes. Reduce: shafts, axles, grinding, bearings, lubrication.

F 30F 5F Fluid friction

Friction in liquids and gases Fc = kv Fc = kv2

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Sliding friction Ffr = kN

µ is the coefficient of friction.

N mg Ftr = µF∂

N = mg – Fsinα Ftr = µ(mg – Fsinα)

N = mgcosα Ftr = µmgcosα Ftr = µmg

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Historical reference

In 1883, the famous Russian engineer and scientist N.P. Petrov wrote: “The force of friction can be noticed always and everywhere, and it must be placed among the most powerful methods by which nature transforms one type of energy into another, gradually replacing them with thermal ones. This force reveals its influence in the most diverse phenomena of nature, arousing the keen interest of scientists of the most diverse directions. Knowledge of the laws of friction is necessary for an astronomer, a physicist, a physiologist, and a technician. This statement by one of the greatest engineers of the end of the last century clearly shows the exceptional importance of tribology - the science of friction and the processes that accompany it.

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Leonardo da Vinci dealt with many issues of machine parts, friction and wear. In the course of his research, he discovered that there is a relationship between load and friction force. He also identified the first laws of dry friction, the essence of which is as follows: The force of friction is directly proportional to the load. The friction force does not depend on the visible (nominal) contact area. The force of friction does not depend on the speed of sliding. Applying these results, he established: The advantages of rolling over sliding. Advantages of line/point contact over area contact. Benefits of ensuring distance between rolling elements in rolling bearings.

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Friction coefficient

The main characteristic of friction is the coefficient of friction μ, which is determined by the materials from which the surfaces of the interacting bodies are made: the friction force F and the normal load Nnormal are related by an inequality that turns into equality only in the presence of relative motion. This relation is called the Amonton-Coulomb law.

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Depending on the type of movement of one body over another, there are: the coefficient of friction in shear - sliding and the coefficient of friction in rolling. In turn, when sliding, depending on the magnitude of the tangential force, the coefficient of incomplete sliding friction, the coefficient of static friction and the coefficient of sliding friction are distinguished. All these friction coefficients can vary over a wide range depending on the roughness and waviness of the surfaces, the nature of the films covering the surfaces.

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The role of friction forces.

The French physicist Guillaume writes very colorfully about the role of friction: “We all happened to go out into icy conditions: how much effort was required to keep from falling, how many ridiculous movements we had to do to resist! This forces us to recognize that the ground we walk on has a precious property that keeps us balanced effortlessly. The same thought occurs to us when we ride a bicycle on slippery pavement or when a horse slides on asphalt and falls. By studying such phenomena, we come to the discovery of the consequences to which friction leads. Engineers are trying to eliminate it in cars - and they are doing well. In applied mechanics, friction is spoken of as an extremely undesirable phenomenon, and this is correct, but only in a narrow special area. In all other cases, we must be grateful to friction: it enables us to walk, sit and work without fear that books and inkwells will fall to the floor. Friction is such a common phenomenon that, with rare exceptions, we do not have to call on it for help: it comes to us by itself. Friction contributes to stability. The carpenters level the floor so that the tables and chairs stay where they are. Dishes, glasses, put on the table, remain motionless without any special care on our part, unless it happens on the ship during the pitching. Imagine that friction can be eliminated completely. Then no bodies, whether they are the size of a stone block or small as grains of sand, will ever rest on one another. If there were no friction, the Earth would be a ball without irregularities, like a liquid drop.”

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Should friction be eliminated?

Let's imagine that all over the world some magician managed to "turn off" the friction. Now think about the unforeseen consequences that would lead to. In the first place, you would, of course, find out that friction is by no means always hard, although it is precisely this friction that is sought to be eliminated in thousands of situations. For example, they lubricate the parts of mechanisms and machines in order to reduce their wear and tear and not waste energy wasted on useless heating. However, without friction, we could not walk, the wheels of cars would spin uselessly in place, clothespins could not hold anything and. etc. Secondly, by now continuing our fantasies together, we would eventually get to the causes that give rise to friction. And here the most interesting opens. During the sliding of one object over another, it is as if the microscopic tubercles are meshing with each other. But if these bumps were not there, then this would not mean that it would be easier to move an object or drag it. There would be a so-called sticking effect, which you can easily detect when, say, trying to move a stack of glossy-covered books along the surface of a polished table. This means that if there were no friction, there would not be these tiny attempts of each particle of matter to keep its neighbors near them. But then how would these particles stick together? In other words, the desire to “live in company” would disappear inside the various bodies. That is, the substance would fall apart to the smallest detail, as a house from a children's designer would crumble into pieces from a concussion. Here is an unexpected conclusion that can be reached if we assume the absence of friction. Friction must be fought, but it will not be possible to completely get rid of it, and it is not necessary. To this we can add that in the absence of friction, nails and screws would slip out of the walls, not a single thing could be held in hands, no whirlwind would ever stop, no sound would stop, but would sound endless echo, relentlessly reflected, for example, from the walls of the room. An object lesson that convinces us of the great importance of friction is given to us every time by black ice. Caught in the street, we are helpless.

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The dependence of the friction force on the area of ​​contact of the rubbing surfaces. Ftr, N 1 0.5 0.25 0 20 28 70 170 S, cm2

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The dependence of the friction force on the size of the irregularities of the rubbing surfaces: wood on wood (various methods of surface treatment).

1) Uneven surface - the bar is not worked out. 2) Smooth surface - the bar is planed along the grain of the wood. 3) Sanded smooth surface treated with sandpaper. 4) In the study of the friction force from the materials of rubbing surfaces, we use 1 bar weighing 120 g and different contact surfaces. We use the formula: F tr \u003d μ N

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We calculated sliding friction coefficients for the following materials:

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Create demonstration experiments; Explain the results of observations;

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Wooden ruler. We put the ruler horizontally on the index fingers of the hands and, slowly, we begin to bring the fingers together. The ruler moves evenly across two fingers at once. She slides in turn on one, then on the other finger. Why? Only the finger that is further from the center of mass of the ruler slides under the ruler, since it experiences less load and less friction. Its sliding stops as soon as it is closer to the center of mass of the ruler than the second finger, and then the second finger begins to slide. So the fingers move towards the center of gravity of the ruler in turn ...

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Conclusions based on the results of the work on the project.

We found out that a person has long been using knowledge about the phenomenon of friction, obtained empirically. Starting from the 15th-16th centuries, knowledge about this phenomenon becomes scientific: experiments are carried out to determine the dependence of the friction force on many factors, regularities are found out. Now we know exactly what the friction force depends on and what does not affect it. More specifically, the friction force depends on: the load or body mass; from the kind of contacting surfaces; on the speed of the relative motion of bodies; on the size of uneven or rough surfaces. But it does not depend on the area of ​​\u200b\u200bcontact. Now we can explain all the regularities observed in practice by the structure of matter, by the force of interaction between molecules. We conducted a series of experiments, did about the same experiments as the scientists, and got about the same results. It turned out that experimentally we confirmed all the statements made by us. We have created a series of experiments to help understand and explain some of the "difficult" observations. But, perhaps most importantly, we realized how great it is to acquire knowledge ourselves, and then share it with others.

Friction force. Friction in nature and technology

The phenomenon of friction The interaction that occurs at the point of contact of the bodies and prevents their relative motion is called friction, and the force characterizing this interaction is called the friction force.

Friction force The force arising from the movement of one body on the surface of another, applied to the moving body and directed against the movement, is called the friction force

Types of friction Static friction Sliding friction Rolling friction

Rest friction The force of static friction prevents the relative displacement of the bodies in contact. It grows along with the force that strives to move the body from its place.

Sliding friction The force arising from the movement of one body on the surface of another and directed in the direction opposite to the movement is called the force of sliding friction.

Rolling friction If a body rolls on the surface of another body, then the friction that occurs at the point of contact is called rolling friction.

Comparison of sliding friction force and rolling friction force Under identical loads, the rolling friction force is much less than the sliding friction force.

Causes of friction 1. Roughness of surfaces of contacting bodies. 2. Molecular attraction acting at the points of contact of rubbing bodies.

Measuring Friction Let's look at the video how it's done.

Experiments of Leonardo da Vinci Scientists have long been interested in what determines the force of friction. Leonardo da Vinci in 1500 studied the dependence of the friction force on the material from which the bodies are made, on the magnitude of the load on these bodies, on the degree of smoothness or roughness of their surfaces.

Comparison of forces of friction sliding, rolling and body weight P > F tr. until > F tr. sk > F tr. quality

Study of the dependence of the sliding friction force on the type of rubbing surfaces The friction force depends on the properties of the contacting bodies (on the type of surfaces).

Study of the dependence of the sliding friction force on pressure and independence of the area of ​​rubbing surfaces The friction force depends on the pressure force and does not depend on the areas of rubbing surfaces.

Friction: good or bad? Strengthen Weaken Increase roughness Increase load Lubrication Bearings: ball and roller Air cushion

The Role of the Friction Force in Walking In the absence of static friction, neither humans nor animals could walk on the ground.

Driving on slippery surfaces Walking on ice is not easy because the friction that occurs between the surface of the ice and the sole of the shoe is small. How can you make walking on slippery surfaces easier?

Lubrication In the presence of lubrication, it is not the surfaces of the bodies that are in contact, but its adjacent layers. Friction between liquid layers is weaker than between solid surfaces.

Bearings The inner ring of the bearing is mounted on a shaft that does not slip during rotation, but rolls on balls or rollers.

Air Cushion An air cushion is an area of ​​increased air pressure between the base of the machine and the support surface that prevents direct contact between the two. Hovercraft

Friction force Friction force is a force that characterizes the interaction of bodies, preventing the relative motion of bodies.

• The friction force is a force that characterizes the interaction of bodies, preventing the relative movement of bodies.
• It is denoted by the letter F with the index tr.
• Measured in newtons.

• Friction force - Ftr. -
• is the force generated by the movement of one body on the surface of another, attached to the moving body and directed against movement.

• Friction is the interaction that occurs when one body comes into contact with another and prevents their movement.

• -occur on contact
• - act along the surface;
• - always directed against the direction of movement of the body.
• Friction forces occur at two adjoining bodies at the same time.

• The contact surfaces of the bodies are never perfectly flat and have
• bumps. Moreover, the places of the protrusions on one surface do not coincide with the places of the protrusions on the other. But under compression, the pointed peaks are deformed and the contact area increases in proportion to the applied load. It is the shear resistance in the places of irregularities that is cause of friction.

• In addition, we must not forget that in the case of ideally smooth surfaces, resistance to movement will arise due to the forces of attraction between molecules.
• This explains the effect on the friction force of the load - the pressing force and the properties of materials.

• surface roughness of contacting bodies

• mutual attraction of molecules of contacting bodies

• Occurs in the case of smoothly sanded surfaces

• As a rule, in most cases, friction is due to this cause.

• Three types of friction forces:
• 1. Sliding friction force (sled) - occurs when one body slides over the surface of another.
• 2. Rolling friction force (wheels) - occurs if one body rolls on the surface of another.
• 3. The force of static friction (in order to move any body, it is necessary to apply some kind of force)
• The static friction force is the force that appears between the contacting surfaces of bodies that are motionless relative to each other.

• Which is better, sliding or rolling? Of course, rolling is more profitable than sliding.
• To keep rolling, you need to apply much less force than to keep sliding at the same speed. Therefore, it is clear that in the summer they ride in a cart, and not in a sleigh.

• But why do the wheels give way to skids in winter? The thing is that wheels are more profitable than skids only when they roll. And in order for the wheels to roll, there must be
• firm, smooth road and also non-slip.

• Liquid Dry
• (friction in gases
• and liquids)
• Feature of fluid friction: there is no static friction force (even with small impacts on the body, it starts to move)

• What does the force of friction depend on?

• 1) on the kind of contact surfaces
• 2) on the magnitude of the load.

• Ways to reduce the force of friction.

• grinding of rubbing surfaces

• lubricant application

• replacement of sliding friction by rolling friction.

• Ways to reduce friction force:- grinding of rubbing surfaces,
• - application of lubrication and replacement of sliding friction by rolling friction.
• The friction force is electromagnetic in nature.

• At one time, the great Italian artist and scientist Leonardo da Vinci, surprising those around him, conducted strange experiments: he dragged a rope along the floor, either in full length, or collecting it in rings. He studied whether the force of sliding friction depends on the area of ​​the bodies in contact.
• As a result, Leonardo came to the conclusion that the force of sliding friction does not depend on the area of ​​the bodies in contact, which is also confirmed by modern scientists.

• This can be done with a dynamometer. With a uniform movement of the body, the dynamometer
• shows the traction force equal to the friction force. For ease of measurement, sometimes instead of
• pull the book on the table, you can begin to move the table itself, and hold the book in place by tying it to the spring. The force of friction will not change.
• The unit of measurement of the friction force in SI (like any other force) is 1 Newton.

• By measuring the force with which the dynamometer acts on the body during its uniform motion, we measure the friction force.
• The greater the force pressing the body to the surface, the greater Ftr;
• For equal loads, the rolling friction force is always less than the sliding friction force.

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FRICTION
Borta Olga Anatolyevna. GBOU Gymnasium No. 1531, physics teacher

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What force changes the speed of these bodies?

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What is friction and friction force?
Friction is the process of interaction of solid bodies during their relative motion (displacement) or during the motion of a solid body in a gaseous or liquid medium. Friction force - a force that occurs at the point of contact of bodies and prevents their relative movement

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Types of friction forces
static friction force
sliding friction force
Rolling friction force

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Causes of Friction
1. Roughness of surfaces: irregularities cling to each other, deform, elastic forces arise, which together create a force that prevents movement
2. If the surfaces are well polished, then the mutual attraction of the molecules of the contacting bodies also prevents movement.

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Features of friction forces:
-occur on contact - act along the surface; - always directed against the direction of movement of the body.

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FRICTION AND MOVEMENT

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Types of friction
Sliding friction is a force arising from the translational movement of one of the interacting bodies relative to the other and acting on this body in the direction opposite to the direction of sliding

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The force of sliding friction arises when one body slides over the surface of another. Depends on the weight of the body and the material of the contacting surfaces, but does not depend on the area. The sliding friction force is less than the static friction force.

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Rolling friction - the moment of forces arising from the rolling of one of the two interacting bodies relative to the other and opposing the rotation of the moving body

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If the body does not slide, but rolls on the surface of another, then the friction is called rolling friction. The rolling friction force is less than the sliding friction force.

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FRICTION AND REST

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The static friction force exists between any bodies at rest. It keeps bodies on an inclined plane. When you try to move the body, the static friction force prevents this action.
Ftr

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FRICTION IN TECHNOLOGY

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DRY FRICTION
Dry, when the interacting solids are not separated by any additional layers / lubricants - a very rare case in practice. A characteristic distinguishing feature of dry friction is the presence of a significant static friction force.

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VISCOUS FRICTION
Liquid (viscous), in the interaction of bodies separated by a layer of a solid body (graphite powder), liquid or gas (lubricant) of different thickness - as a rule, occurs during rolling friction, when solid bodies are immersed in a liquid.

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MIXED FRICTION, when the contact area contains areas of dry and liquid friction. BOUNDARY, when the contact area may contain layers and areas of various nature (oxide films, liquid, etc.) - the most common case in sliding friction.

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We have no friction, guys, and neither here nor there!

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How can you use the studied phenomenon in life?
The phenomenon of friction is used in technology: - to transfer motion; - in the processing of metals and other materials; - in friction welding; - when sharpening tools; - for fastening materials, construction details; - when grinding, polishing materials, etc.

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Friction reduction
Lubrication Material selection Roughness reduction Application of rolling friction instead of sliding friction

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Increase in friction
If friction is useful, it is increased by increasing the roughness of the surfaces: the tires are ribbed, the dowel is a wall mount, slippery roads are sprinkled with sand.

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FRICTION IN NATURE

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Friction in a person's life
The problem of friction and wear in the joints is solved by nature at a level that tribologists can only dream of so far. Daily loads, for example, in the human hip joint exceed a thousand newtons when jumping, and friction and wear are practically absent. The result is trouble-free operation for a lifetime!

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Friction in animal life
Under the action of organs of motion in animals and humans, friction manifests itself as a useful force. To increase traction with the ground, tree trunks, there are a number of different adaptations on the limbs of animals: claws, sharp edges of hooves, horseshoe spikes, the body of reptiles is covered with tubercles and scales.

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In the life of many plants, friction plays a positive role. For example, creepers, hops, peas, beans, and other climbing plants, due to friction, can cling to nearby supports, hold on to them, and reach for the light. A sufficiently large friction occurs between the support and the stem, because the stems repeatedly wrap around the supports and fit very tightly to them.

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But plants that have root crops, such as carrots, beets, rutabaga. The force of friction on the ground helps to keep the root crop in the soil. With the growth of the root crop, the pressure of the surrounding earth on it increases, which means that the friction force also increases. That is why it is so difficult to pull large beets, radishes, turnips out of the ground.

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For plants such as burdock, friction helps to spread the seeds, which have spines with small hooks at the ends. These spines are hooked on the fur of animals and move along with them. Seeds of peas, nuts, due to their spherical shape and low rolling friction, move easily on their own.

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FRICTION: HARM OR BENEFIT?

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Is friction beneficial or harmful?
The low friction due to the lubricating action of the water is the reason why many accidents at home occur in the bathroom. To understand this, let's first think about why we wear shoes? When we walk, our feet push off the floor, and this is only possible due to friction. Shoes are able to provide better grip of the soles with the floor, more friction.