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Presentation on the topic of ubiquitous friction. Presentation is friction. So that we don't get tired

27.04.2021

Friction force

Slides: 20 Words: 560 Sounds: 0 Effects: 76

Friction. Friction ... Harmful or Good? Purpose of the project: To find out the significance of the friction force in the surrounding life and technology. Find out: the force of friction is an enemy or an ally of a person? Project objectives: To identify the causes of frictional forces. Study the types of friction force. Identify ways to reduce and increase friction force. Friction will wear out the moving parts of the machines. Friction makes it difficult to move heavy objects. Friction is a waste of energy. Our hypothesis. Friction is always harmful! Research progress. Group 1 tasks: Causes of friction. Intermolecular attraction. Surface roughness. - Friction force.ppt

Friction force

Slides: 14 Words: 142 Sounds: 0 Effects: 0

Friction force. Friction is one of the types of interaction between bodies. Friction is a familiar but mysterious force. But in other cases, friction is harmful. Examples. Making fire by primitive people. Making fire in a modern way. Moving an object from place. Skating. Lacing sneakers. Vehicle movement (wheel friction against the road). Screwing in a screw. Writing by pen on paper. - Friction force.ppt

Friction force physics

Slides: 6 Words: 93 Sounds: 0 Effects: 18

Physics presentation on the topic: friction force. Definition. Direction. The frictional force is directed in the opposite direction to the movement. Causes of occurrence. Roughness of surfaces of contacting bodies. Mutual attraction of molecules of adjoining bodies. Types of friction forces. The friction force is of three types: 1. Sliding friction. 2. Rolling friction. 3. Rest friction. Formula for finding the friction force. Ftr =? * N? - friction coefficient n - support reaction force. - Friction force physics.ppt

Physics Friction force

Slides: 32 Words: 836 Sounds: 0 Effects: 0

Physics lesson in grade 7. Friction force. FRICTION IS A FAMILIAR POWER BUT MYSTERIOUS A.A. Pervozvansky. Lesson objectives: Lesson objectives. Repetition. Conversation, frontal polling, individual work at the blackboard and in the field. Review questions. What is strength? By what signs do we judge that a force has acted on the body? What determines the result of the action of force? In what units is force measured? How is force depicted in a drawing? What device is used to measure force? What powers do you know? Give examples. What force is called the resultant force? Formulation of the problem. Why can't you move a heavy drawer or cabinet right away? - Physics Friction Force.ppt

Friction force grade 7

Slides: 6 Words: 101 Sounds: 0 Effects: 0

Friction force. Physics grade 7. Types of dry friction. Friction at rest is a force between bodies at rest relative to each other. When solids move in liquids, a viscous friction force arises. Friction in nature. Friction in technology. - Friction force grade 7.ppt

Grade 7 lesson Friction force

Slides: 20 Words: 752 Sounds: 0 Effects: 21

Lesson topic: "friction force". Zarubino Bernatskaya Evgenia Vladimirovna. Homework check. What to do? Why sprinkle with sand? Lesson topic: "friction force". Fill in the table according to the picture. Friction force. Static friction force. Rolling friction force. Sliding friction force. Practical work “Measuring force. For example, such friction occurs when sleds and skis move through the snow. SLIDING FRICTION FORCE arises from sliding friction. ROLLING FRICTION is generated by rolling friction. Friction force of rest arises during friction at rest. Practical work "Measurement of friction force". PURPOSE: To find out what values the friction force depends on. - Grade 7 lesson Friction force.ppt

Physics Grade 7 Friction Force

Slides: 10 Words: 200 Sounds: 0 Effects: 41

Friction force. The frictional force holds the bar on an inclined plane. The friction force is directed against the movement of the body. Causes of friction: 1. The presence of roughness (irregularities). 2. Attraction of molecules of adjoining bodies. Types of friction: 1. Friction at rest. 2. Sliding friction. 3. Rolling friction. Reducing friction: 1. Lubrication. 2. Bearings. 3. Air cushion. Increased friction. Roughness (sand, treads, grooved soles, etc.) Load ... .. Explain the proverbs: If you don't grease, you won't go. You can't hold an eel in your hands. What's round is easy to roll. The well rope is fraying. - Physics Grade 7 Friction Force.ppt

"Friction force" grade 9

Slides: 20 Words: 1959 Sounds: 0 Effects: 0

Study of the friction force and its role in human life. Introduction. Educational project. Research team report. Experimental group report. Friction trial. Friction. Friction is blamed for interfering with walking. Collectors of folklore. Historians. During the 18th and 19th centuries, there were up to 30 studies. Experimenters. Dependence of the friction force on the size of the irregularities. The challenge for practitioners. Knowledge about the phenomenon of friction. - "Friction force" class 9.pptx

"Friction force" grade 10

Slides: 13 Words: 713 Sounds: 0 Effects: 32

Friction force. The force that arises when one body moves along a surface. Types of friction. Causes of friction force. A table for memorizing formulas. The sword is a bone process of the upper jaw of a fish. It's about a multiple winner. How friction is reduced and increased. What force must be applied to the sleigh. How can the friction force be increased. An entertaining fact. Determination of the sliding friction coefficient. Rubbing materials. - "Friction force" class 10.ppt

Frictional force action

Slides: 30 Words: 524 Sounds: 0 Effects: 21

Strive to comprehend science more and more deeply. What is strength. The phenomenon of friction. The force arising from the contact of the surfaces of bodies. The first study of the laws of friction. Friction laws. Friction coefficient. Coefficients of friction. If the body is rolling. When trying to move the body. Friction force. Bar. Roughness. Causes of friction. Useful friction. Manufacturing friction. The action of the friction force. Moving parts. Harmful friction. Reducing harmful friction. Increased effective friction. - The action of the friction force.ppt

Examples of frictional forces

Slides: 25 Words: 602 Sounds: 1 Effects: 70

Friction force. Definition. Direction. Causes of occurrence. Types of friction forces. Formula for finding the friction force. Static friction force. Objective of the project. Content. The static friction force is the force acting on the body. The properties of the static friction force. The formula for finding the static friction force. The force of friction at rest in folk art. Sliding friction force. The force that occurs when one body slides over the surface of another. Examples of frictional forces. Strength properties. Friction and sports. Rolling friction. Rolling friction is the moment of forces that occurs during rolling. Description. Rolling friction in technology. Special tires. - Examples of friction force.ppt

Determination of friction force

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Friction force. Friction. Phonons. Views. Sliding friction. Rolling friction. Rest friction. It is customary to separate friction. Solid bodies. Layers and patches. Areas of dry and liquid friction. Liquid. Internal friction. Friction processes. Friction coefficient. Friction in mechanisms and machines. The amount of friction. Surface grip. - Determination of friction force.pptx

Investigation of the friction force

Slides: 41 Words: 3847 Sounds: 0 Effects: 0

Friction forces and SRT. Friction forces. Friction force. Horizontal surface. The bar is on the table. Friction laws. Friction or adhesion. Friction forces in the animal kingdom. Polypropylene microfibers. Anisotropic friction. The movement of a solid in a liquid medium. Roughness of the body. "Liquid" friction. Universe. Galaxies. Spatial structure of the Universe. The sun. Galileo's principle of relativity. Galileo's transformations. Coordinate relations. Body acceleration. Equations of mechanics. Galileo's transformations. HUNDRED. The principle of the constancy of the speed of light. The speed of the atomic electron. Time in different reference systems. -

Presentation on the topic "Friction force" in physics in powerpoint format. The purpose of this presentation for schoolchildren is to acquaint students with the force of friction, to show the role of the force of friction in nature and technology. Auto presentations Ladanova Irina Vladimirovna, physics teacher.

Fragments from the presentation

The sledge, having rolled down the mountain, stops after a while. This means that a force was acting on the body. When one body comes into contact with another, an interaction occurs, which is called friction

The force arising from the interaction of the surface of one body with the surface of another, when the bodies are stationary or move relative to each other, is called by the power of thorns.

Cause of friction force

Surface roughness
Mutual attraction of molecules

Types of friction forces

Rolling friction
Sliding friction
Rest friction

Sliding friction force

If a body slides on the surface of another, then the resulting force is called sliding friction

Rolling friction force

If a body rolls on the surface of another, then the force arising from this is called rolling friction

Static friction force

When trying to move the body from its place, it will not immediately change its speed, since the force acting on the body is balanced static friction

Frictional force in plants

Due to friction, climbing plants cling to nearby supports, hold and stretch towards the light
The force of friction against the soil of root crops helps to keep the plant in the soil
For plants like burdock, friction helps spread seeds that have spines with small hooks at the ends.

Frictional force in animals

The action of the organs of grasping in animals (limbs, trunk of an elephant) is associated with friction. The more firmly the object will be gripped, the greater the force of friction between the organ of grasping and the object

Frictional force in technology

In all machines, friction causes moving parts to heat up and wear out.
Bearings help reduce the friction force tenfold by replacing rolling friction with sliding friction

Questions to consolidate:

Why is the bow rubbed with rosin before the game?
Why do I polish medical needles to a mirror finish?
Why does polishing and grinding mating parts reduce friction? Will the friction force be reduced if the surfaces of the parts are perfectly polished?
For what purpose are sewing needles polished to a shine? Is it convenient to sew with a rusty needle?
A book and a ball are on the table in the train carriage. The train started to move. What happens to the ball and the book?
Racing bikes have a low handlebar. Why?
Why is live fish difficult to handle?

Slide 1

Friction force

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

Prepared by: physics teacher Mingazova Maysara Valeevna

Slide 2

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

Objectives: 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; Carry out experiments confirming the patterns and dependences of the friction force; To think over and create demonstration experiments proving the dependence of the friction force on the force of normal pressure, on the properties of the contacting surfaces, on the speed of the relative motion of bodies.

Slide 3

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?"

Slide 4

Frictional force in nature

Slide 5

Slide 6

Is friction good or bad?

Slide 7

We studied proverbs, sayings, fairy tales, in which the force of friction, rolling, rest, sliding is manifested, we studied human experience in the use of friction, methods of combating friction.

Slide 8

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. It's hard to swim against the water. Do you like to ride, love to carry sledges. Patience and work will grind everything.

Proverbs and sayings:

Slide 9

"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" - friction at rest. "Bear's slide" - sliding friction.

Slide 10

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

Slide 11

1. Introduction between rubbing surfaces of lubricant (for example, any oil). 2. The use of ball and roller bearings. 3. Application of an air cushion.

Ways to reduce friction:

Slide 12

The first rolling bearing made of metal was supported by a windmill built in 1780 in England at Sproveston.

Slide 13

Bearing of the period of the technical revolution from 1500 to 1850

Machine tool bearings with split adjustable bearing blocks

Slide 14

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

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

Slide 15

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

Slide 16

Friction forces

Quiescent Slide Rolling

Ftr = Ftr Ftr V

When in contact Along the surface Forcing movements

electromagnetic

Slide 17

The phenomenon of 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 a gas or liquid)

Friction force Ftr as a characteristic of the surface action on the body. The nature of the friction force: a) depends on the material of the body and surface, lubricant, the value of N; b) does not depend on the S surface; c) Fmax at rest is greater than F slip; d) F rolling is less than F slip; The law of friction force (for the case of independence of speed) Ffr = 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 sliding bearings. Increased friction: sand on the road with ice, chains on wheels, special tires, tread on boots, etc. Calculation of the movement of bodies. Calculation of deformations.

Slide 18

Rest friction

Ftr. rest = - F (Ftr. p) max = µN Friction at rest - driving force, "coupling weight".

Rolling friction

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

F 30F 5F Liquid friction

Friction in liquids and gases Fc = kv Fc = kv2

Slide 19

Sliding friction Ftr = kN

µ is the coefficient of friction.

N mg Ffr = µF∂

N = mg - Fsinα Ftr = µ (mg - Fsinα)

N = mgcosα Ftr = µmgcosα Ftr = µmg

Slide 20

Historical reference

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

Slide 21

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 frictional force. He also defined the first laws of dry friction, the essence of which is as follows: The friction force is directly proportional to the load. The friction force is independent of the visible (nominal) contact area. The friction force is independent of the sliding speed. Applying these results, he established: The advantages of rolling over sliding. Advantages of line / point contact over area contact. Advantages of maintaining the distance between the rolling elements in rolling bearings.

Slide 22

Friction coefficient

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

Slide 23

Depending on the type of movement of one body over another, there are: the coefficient of friction during shear - sliding and the coefficient of friction during rolling. In turn, during 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 coefficients of friction can vary widely depending on the roughness and waviness of the surfaces, the nature of the films covering the surfaces.

Slide 24

The role of friction forces.

French physicist Guillaume writes very colorfully about the role of friction: “We all happened to go out on ice: how much effort it took to keep from falling, how many funny movements we had to do to resist! This forces us to recognize that the earth we walk on has a precious property that helps us maintain our balance effortlessly. The same thought occurs when we ride a bicycle on a slippery pavement or when a horse slides on the asphalt and falls. Studying such phenomena, we come to the discovery of the consequences to which friction leads. Engineers strive to eliminate it in cars - and they do well. In applied mechanics, friction is spoken of as an extremely undesirable phenomenon, and this is correct, but only in a narrow, specialized field. In all other cases, we should be grateful for friction: it allows us to walk, sit and work without the fear of books and inkwell falling to the floor. Friction is such a widespread phenomenon that we, with rare exceptions, do not have to call it for help: it appears to us by itself. Friction promotes stability. Carpenters level the floor so that tables and chairs remain where they are. Dishes, glasses, placed on the table, remain motionless without any special care on our part, unless it happens on the steamer during the pitching. Let us imagine that friction can be completely eliminated. Then no bodies, be they the size of a block of stone or as small as grains of sand, will never hold one on top of the other. If there were no friction, the Earth would represent a sphere without irregularities, like a liquid drop ”.

Slide 25

Do you need to get rid of friction?

Imagine that all over the world a certain magician has succeeded in “turning off” friction. Now think about the unforeseen consequences of this. First, you would, of course, find out that friction is by no means always firm, although it is precisely this friction that people seek to get rid of in thousands of situations. For example, they lubricate the parts of mechanisms and machines in order to reduce their wear and not waste energy that goes into useless heating. However, without friction, we would not be able to walk, the wheels of cars would spin in place uselessly, clothespins would not be able to hold anything and. etc. Secondly, now continuing our fantasies together, we would eventually get to the causes of friction. And here the most interesting thing opens up. 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, this would not mean that it would be easier to move the object or drag it. There would be a so-called sticking effect, which you can easily discover when trying, say, to slide a stack of glossy-coated books along the surface of a polished table. This means, if there were no friction, there would not have been these tiny attempts of every particle of matter to keep its neighbors close to itself. But then how would these particles stick together at all? In other words, the desire to “live in company” would disappear inside various bodies. That is, the substance would fall apart to the smallest detail, as a house from a children's construction set would crumble to pieces from a shock. This is an unexpected conclusion that can be reached if we assume that there is no 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 one thing could be held in the hands, no whirlwind would ever stop, no sound would cease, but would sound an endless echo, echoing relentlessly, for example, from the walls of the room. An object lesson that convinces us of the enormous importance of friction is given to us every time by icing. Caught up in the street, we are helpless.

Slide 28

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

Slide 29

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

Slide 30

We have calculated sliding friction coefficients for the following materials:

Slide 31

Create demo experiments; Explain the observation results;

Slide 32

Wooden ruler. We put the ruler horizontally on the index fingers and, slowly, we begin to bring the fingers together. The ruler moves evenly over two fingers at once. She slides in turn one by one, then the other finger. Why? Only the finger farther from the center of mass of the ruler slides under the ruler, as it experiences less stress 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 to the center of gravity of the ruler alternately ...

Slide 33

Conclusions based on the results of 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, and regularities are clarified. Now we know exactly what the friction force depends on and what does not affect it. More specifically, the friction force depends on: load or body weight; from the kind of contacting surfaces; on the speed of the relative movement of bodies; on the size of irregularities or surface roughness. But it does not depend on the contact area. Now we can explain all the regularities observed in practice by the structure of matter, by the force of interaction between molecules. We ran 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, probably, the most important thing is that we realized how great it is to acquire knowledge ourselves, and then share it with others.

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

Causes of frictional forces Roughness of surfaces of contacting bodies thereby interfering with movement.)

Static frictional force Why can't you move a heavy drawer or cabinet right away? Why can't you move a heavy drawer or cabinet right away? To move from the support, you need to apply force. This force balances the static friction force. To move from the support, you need to apply force. 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 car tires wear out. The soles of shoes and car tires wear out.

Ways to reduce friction Treatment of rubbing surfaces to a smooth state. Treatment of rubbing surfaces to a smooth state. Replacing sliding friction with rolling friction. Replacing sliding friction with rolling friction. Use of lubricant. Use of lubricant.

Friction in nature Many plants and animals have various organs that serve for grasping (antennae of plants, the trunk of an elephant, prehensile tails of climbing animals). All of them have a rough surface to increase the frictional force. Many plants and animals have various organs that serve for grasping (antennae of plants, the trunk of an elephant, prehensile tails of climbing animals). All of them have a rough surface to increase the frictional force. 1. What are the forces of friction? a) Sliding friction. c) Friction at rest. b) Rolling friction. d) All named species. 2. In what cases presented here is the rolling frictional force occurring? 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 At what type of friction of bodies occurs the smallest friction force? a) With rolling friction. b) In the case of sliding friction. c) With friction at rest. d) For all types of friction, the forces are the same. 5. How can friction be reduced? a) Lubricate the surfaces of the contacting bodies. b) Press the bodies together. c) Increase the roughness. d) Polish the surfaces. Test
Homework Explain these sayings about friction: If you don't grease, you won't go. If you don't grease it, you won't go. It went smoothly. It went smoothly. You can't hold an eel in your hands. You can't hold an eel in your hands. That rolls round easily. That rolls round easily. The skis glide according to the weather. The skis glide according to the weather.

Friction force

There is a friction force in the world,

It matters a lot!

three types of friction: sliding, resting, rolling.

Everyone in themselves is very important

And in this world, of course they are needed!

Physics teacher MBOU "Mokhchen secondary school"

Chuprova Galina Robertovna

The frictional force is the force that occurs when

movement of one body on the surface of another

F tr

Frictional force is always directed

opposite movement

Causes of friction force:

mutual attraction of molecules of adjoining bodies.

Uneven contact surfaces

Only at the end of the 18th century, the scientists G. Amonton and Sh.O. A new physical constant was introduced for the pendant - the coefficient of friction (k). After that, a formula for the friction force was derived: Ftr = kN, where N is the support reaction force corresponding to the pressure force exerted by the body on the surface.

The friction force depends on :

- the force of gravity acting on a moving body;

- surface quality;

- areas of rubbing surfaces;

- the type of friction.

The contacting surfaces of bodies are never perfectly flat and have irregularities.

There are several types of friction

If the body is difficult to move

Friction can be reduced.

Humanity has long invented the wheel.

There is friction, rolling friction.

Dry friction arises when solid bodies in contact move relative to each other.

Sliding friction occurs when one body slides over the surface of another.

Rolling friction occurs when one body rolls on the surface of another.

Viscous (otherwise liquid) friction occurs when solid bodies move in a liquid or gaseous medium, or when a liquid or gas flows past stationary solids.

Rest friction occurs when a force is applied to a body to move that body.

How to measure frictional force?

This can be done with a dynamometer.

With a uniform movement of the body, the dynamometer shows a traction force equal to the friction force.

Fizminutka

So that we don't get tired

It is necessary to give the body a rest.

We'll break up with you quickly

And we will return to the place again. We will rub the muscles of the thighs

We will remember friction while

Benefit from friction here

From sliding friction.

We knead the muscles of the shoulders

We remember friction again

We clasp our hands together

There will be friction at rest.

Friction

Useful

Harmful

when walking
- hold objects
-stopping the car - starting the movement of the car
when writing
- brush your teeth
- apply a bandage
- wear clothes
- light a fire, etc.

the moving parts heat up and wear out parts of machines
- creak of doors, floors
- calluses on the legs and arms
- joint pain

Useful friction

Friction helps humans and animals walk on the ground.

If there was no friction between the bodies, we would not be able to take our hands. The soles of the sneakers are made of grooved rubber to increase their friction on the ground. Friction is used in many mechanisms. A kind of "pattern" is applied to the surface of the tire. It improves the grip of the rubber on the road. To increase friction in ice, sidewalks are sprinkled with sand

Harmful friction

Friction inhibits movement; An enormous amount of valuable fuel is consumed to overcome all types of friction. Friction causes wear on the rubbing surfaces. A lubricant is used to reduce friction. In moving parts of machines, bearings are used, in which sliding friction is replaced by rolling friction. Fish and birds have a streamlined body that also reduces friction. Therefore, cars, planes and rockets are streamlined.

you won't grease, you won't go;
business went like clockwork;
you can't hold an eel in your hands;
what is round rolls easily;
skis slide in the weather;
you cannot weave a net from a waxed thread;
the well rope is fraying;
a rusty plow is cleaned only on plowing;
there is no such person who has not slipped on the ice at least once.

WE WILL SOLVE THE PROBLEMS

Why is it easier to swim than to run on the bottom up to the waist submerged in water?

Why is the flow of water in the river near the banks and the bottom slower than in the middle and on the surface?

Why is it difficult to hold live fish in your hands? And lifeless too?

Why does a loaded ship move slower than an unloaded ship?

1. Consider carefully how some light cotton fabric is woven from threads, for example, chintz, satin, gauze, etc. What would happen to the fabric if not for the friction? What material is the most "capricious", it crumbles heavily when sewing?

2. The needles are polished to a high shine. What is the purpose of such a thorough polishing? Why is it difficult to sew with a rusty needle?

3. Guess the riddle and answer the question: "A bucket rough as a grater on a finger." Why is this bucket made rough?

1. Why does a skier, swiftly descending a mountain, roll further along the flat horizontal surface of a snow field at a decreasing speed?

2.Why are they stuffed with leather, plastic, metal spikes on the soles of footballers' sports shoes (boots, spikes)? 3. Why does the goalkeeper of a football team wear special gloves with a thin layer of rough rubber on the palms and fingers during the game? 4. Why, when diving from the platform, the swimmer strives to enter the water in a vertical rather than horizontal position?

Give a physical justification for the proverb: “Mow, scythe, while the dew is; the dew is gone, and we are home. " Why is it easier to cut the grass with dew?

Why should the cutting parts of a plow, mower, straw chopper and other agricultural implements and machines be sharpened sharply?