The force of friction occurs literally at every step. But do people know why it is needed? What are the harms and benefits of friction? Let's try to figure it out.
Preface
Several forces act on earthly objects, which are closely interconnected and affect the vital functions of bodies. First of all, this is the force of gravity, elasticity ( internal resistance bodies in response to the displacement of their molecules) and support reactions. But there is also a very important physical quantity called friction force. Unlike gravity and elasticity, it does not depend on the location of bodies. When studying it, other laws apply: the sliding friction coefficient and the support reaction force. For example, if you need to move a heavy cabinet, then from the very first minute it will become clear that this is not easy to do. In addition, there are certain interferences when performing this task. What hinders the efforts put into the cabinet? And what prevents this is nothing more than the force of friction, the principle of which is studied in school. The 7th grade physics course talks about this phenomenon in detail.
What's under our feet?
People encounter it very often. The benefit of friction is that we would not be able to take a step without this physical quantity. It is what holds our shoes on the surface where we step. Each of us has walked on very slippery surfaces, such as ice, and knows firsthand that it is very difficult. Why is this happening? Before we talk about the harm and benefit of friction, let’s define what it is.
The essence of the concept
The friction force is the interaction of two bodies that occurs at the point of their contact and prevents their movement relative to each other. There are several types of friction - resting, sliding and rolling.
Causes
The first reason is the constant roughness of surfaces. It is this indicator that influences what type of friction force will occur. If we are talking about smooth surfaces, for example, a metal-covered roof or icy areas, then their roughness is almost invisible, but this does not mean that it is not there - it is present at a microscopic level. In this case, the sliding friction force will act. But if we talk about a cabinet standing on a carpet, then the roughness of the two objects will significantly impede mutual movement. The second reason is electromagnetic molecular repulsion, which occurs at the point of contact of objects.
Static friction
What happens when we try to move a cabinet, but we cannot move it even an inch. What holds an object in one place? This is the static friction force. The fact is that the applied efforts are compensated by the force of dry friction that occurs between the cabinet and the floor.
Harms and benefits of static friction force
It is the force of static friction that prevents the laces on our shoes from unraveling on their own, preventing the nail that we just hammered into the wall from falling out, and holding the cabinet in place. Without it, it would be impossible for neither people, nor animals, nor cars to move on the earth's surface. Friction damage is also present. It happens on a fairly global scale; for example, the force of static friction can lead to deformation of the skin of ships.
Scientific background
In order to move the cabinet, it is necessary to apply a force to it that exceeds friction. That is, as long as the forces applied are less than the friction force, the furniture will remain in place. In addition to these factors, there is also a support reaction force, which is directed perpendicular to the plane. It depends on the material from which the floor is made (elasticity is also involved here). There is also a coefficient of friction depending on what the two surfaces interacting with each other are made of. Therefore, the friction force acting on the cabinet is equal to the friction coefficient, which is multiplied by the reaction force of the support (surface).
Sliding friction
So, to overcome the friction, we asked someone to help us move the cabinet. What did we find? That after we applied a force that exceeded the force of static friction, the cabinet not only moved, but also continued to move in the required direction for some time, of course, with our help. And the effort spent was approximately the same throughout the entire journey. In this case, we were hampered by the sliding friction force, directed in the direction opposite to the applied force. It is worth noting that its resistance is much lower than that of the static friction force. To reduce this indicator, various lubricants.
Rolling friction force
If we remember that someday we will have to move the cabinet back, we will decide to equip it with wheels. In this case, the resulting interaction will be called rolling friction, since the object will no longer slide, but roll along the surface. The rolling wheels will press slightly into the carpet, forming a bump that we will need to overcome. This determines the rolling friction force. Of course, if we roll the cabinet not on the carpet, but, for example, on the parquet, then it will be even easier to move it, due to the fact that the surface of the parquet is harder than the surface of the carpet. For the same reason, cyclists find it much easier to ride on a highway than on a fine sand beach.
Ambiguous question
What are the harms and benefits of any type of friction force? Of course, the examples given are somewhat exaggerated - in life everything is a little more complicated. However, despite the fact that the force of friction has obvious disadvantages that create a number of difficulties in life, it is clear that without it there would be many more problems. Therefore, this value has its disadvantages and advantages.
Negative examples
Among the examples of the harm of this force, one of the first places is the problem of moving heavy loads, quickly wearing out favorite things, as well as the impossibility of creating a perpetual motion machine, since due to friction, any movement sooner or later stops, requiring third-party intervention.
Positive points
Examples of the usefulness of this force include the fact that we can walk comfortably on the ground without slipping at every step, our clothes fit securely and do not instantly become unusable, since the threads of the fabric are held together by friction. In addition, people use the principle of this force by sprinkling slippery roads, due to which many accidents and injuries can be avoided.
conclusions
Humanity has learned to interact with a given physical quantity, increasing and decreasing it depending on the goals set. Our immediate task is to try to use it as efficiently as possible.
The harm and benefits of friction
It’s not going - it’s just going,
Because it's icy
But it falls great!
Why isn't anyone happy?
Such a naive nursery rhyme at first glance - but how much it contains if you look at it from a physical point of view! After all, it is precisely in it that the system of contradictory attitudes towards the notorious force of friction is contained. This constant battle, where two concepts compete with each other - harm and benefit of friction, will never have a winner. After all, what is convenient and beneficial for one person is often quite the opposite for another - bad, as in this poem.
Do you remember Nikolai Nosov’s story about the ice slide that the guys built in the yard? And when they all left for lunch, the one who did not participate in the construction came out. He tried to climb on it, but only hurt himself, but he couldn’t climb. And the kid guessed to sprinkle sand on the ice - it became very convenient to climb to the very top, even on ice! So, using sand to increase the friction force between slippery ice and sole, the boy realized that the benefits of friction make it possible to overcome obstacles.
But after lunch, the kids came out with ice cubes to have a blast on their slide. But that’s not the case: sleds don’t run on sand! For them, this situation turned the other way, showing the harm of friction.
We see similar cases in winter, when boys roll out ice paths and run along them, covering the distance in a matter of minutes! And behind them, elderly people hobble, slip on snow-dusted slopes and fall, breaking their arms and legs. Here you go again illustrative examples, where in the same case both harm and benefit of friction force coexist.
It is to reduce friction that skiers lubricate their skis with special ointments to increase speed when moving. Rinks used by speed skaters or figure skaters are periodically watered and cleaned, also to reduce friction. On the contrary, pedestrian paths are sprinkled with sand or ash so that no one falls on them. Some inventors and innovators even came up with the idea of gluing pieces of sandpaper to the soles of winter boots and boots just to increase the friction force.
The same thing happens with car wheels. It’s no secret that with the onset of winter, drivers “put shoes on” their iron horses to special " winter tires" Otherwise without useful force friction increases braking distances, the car skids when turning, it skids, and often the driver has poor control. And everyone knows for themselves how accidents end.
We’re all talking about winter, and about ice, and about falling. Are there other moments in everyday life where you can clearly see how the harm and benefit of friction compete with each other? Of course have! They are everywhere. Even in our room with you.
Here, for example, is a huge and heavy wardrobe. He stands rooted to the spot and doesn’t move. And if the friction force suddenly disappeared, what could happen then? And this huge thing would move around the room with the slightest push! And it remains to be seen whether we would have been able to dodge it in time. Good strength friction, useful!
But my mother decided to rearrange the furniture. And you need to move this notorious closet to another wall. One - two, they took it! Three - four, tighten up! Only everything turns out to be useless: the heavier the object, the stronger the friction force holds on to it. Horrible, nasty force!
Again they compete with each other - the harm and benefit of friction. There is no need for any competition! You just need to know the physical laws well and be able to derive practical benefit from this knowledge. Not needed in this moment friction force? This means that it should be reduced: make the contacting surfaces smoother and slipperier. To do this, some advise spreading soap or oil on the floor, while others place a wet rag under the legs of a heavy object. And now - one - two - and it’s done! They moved this colossus quite easily from its place.
The force of friction constantly accompanies us throughout our lives, just like the force of gravity. In some places it creates inconvenience for us, and in others we cannot do without it. But be that as it may, it exists, and our task is to learn to use physical laws so that our life becomes more convenient and comfortable.
What are the benefits and harms of friction?
Alexandr Mogilen
For example, in weaving, friction also plays a role important role: prevents the threads from straightening out and the fabric from falling apart into individual threads. As a result of the action of each other, the warp and weft threads bend, taking on a wave-like shape in the fabric.
There are many examples.
What's swinging negative side.... For example, a perpetual motion machine cannot be created due to the force of friction, since wear occurs.
For battleships at their speed, the greatest harm is caused not by the resistance of the form, but by the banal force of friction of water on the hull. And practically nothing can be done with it. Even the best color - the so-called “self-polishing” one, although it reduces it, is far from sufficient to reduce the friction force many times over.
In general, there are many examples of both pros and cons.
Denis Sivtsev
Seventh grade. The role of friction force is very large. For example, thanks to the force of friction we can walk (that is, we interact with the Earth and push off from it), a car can slow down due to the friction of the wheels on the asphalt. But the force of friction is both useful and harmful. If it's icy outside, we can slip up and hurt ourselves (since the friction is small). And it is calculated by the formula: F = umg, where u is the friction coefficient.
Prowling Tiger
The benefit of friction is the adhesion of wheels to asphalt, for example; IMHO, the main harm is the inability to create a perpetual motion machine due to friction, which has already been indicated, but not so much because of wear, but because the full mechanical energy is not conserved...
And the formula written above F=umg, where u (generally “mu” is a Latin letter) is the coefficient of friction, is a special case of the sliding friction force, when the normal component of the support reaction force N is equal to the force of gravity, that is, when the body is lying ( moves) on a horizontal surface, so the formula for the sliding friction force is: F=uN
vika 123
harm or better said disadvantages of this phenomenon:
for example, friction force leads to wear of car parts: bearings, tires, etc.
because of it, some human actions become painful, for example, if your fingers rub against the handle of a shovel during some kind of work, then calluses will appear as a protective reaction of the body
I was asked to write about the harm and benefits of friction in physics, I need a bunch of examples!!! so what is the harm and benefit????/
Pavel M
You don’t need to look far for examples. Just look around. What do you see? Do you see the closet? It turns out that he is standing against the wall thanks to the frictional force that holds him by his legs. In general, all prefabricated furniture is held together solely by friction. This is a simple example. Cars drive along the street and turn at intersections also due to traction with the road, and this is ensured by the force of friction. Ice, snow porridge - poor grip- here's an accident for you.
On the other hand, friction dissipates energy, converts it into heat, and promotes mechanical wear materials. In many cases, friction is the enemy and they try to get rid of it by introducing lubricants and other techniques. For example, in the same car, the engine contains oil precisely to reduce friction. And bearings are designed to convert sliding friction into rolling friction (which is less).
Friction slows down movement; A huge amount of valuable fuel is consumed to overcome friction of all types. Friction causes wear and tear on rubbing surfaces: soles, car tires, and machine parts wear out.
Nobel Prize winner, Swiss physicist Charles Guillaume said: “Let us imagine that friction can be completely eliminated, then no body, be it the size of a stone block or small like a grain of sand, will ever rest on one another, everything will slide and roll until will not be on the same level. Without friction, the Earth would be uneven, like a liquid. ”
Harm and benefit of friction forces
Alien Mind
The damage caused by friction is enormous - for example, a significant part of the energy in various mechanisms is spent on overcoming the friction force. Therefore, they are trying to reduce it with the help of lubricants, bearings and the like. People began to try to reduce the force of friction back in primitive times. Vehicle(carts) using tar, vegetable and animal fats as a lubricant. Later they were developed Various types bearings (too many of them) that reduce the friction force to acceptable values.
The benefits of friction are also enormous - it is thanks to the force of static friction that a person can move forward. Therefore, sometimes they try to increase the friction force - for example, they make the soles of shoes ribbed, apply sand to the ice, car treads are also made ribbed, and even with spikes. In general, they pervert as they want.
An essay on the topic of the benefits and harms of friction. thank you in advance))
Irina Sorokina
slippery shoes.
friction forces in the thread.
balance point.
over the planet. Life in such conditions is unlikely to be possible. . .
sug dfsvf
Friction is both our enemy and our ally.
In some cases, the lack of friction can lead to big troubles (for example,
Braking of cars occurs only due to the friction forces that arise between
pads and drum), and in some cases even minimal friction forces
have the most harmful effects (for example, in mechanical watch and thin
scientific instruments). However, to understand the full meaning of friction, it is necessary to
“turn off” and monitor future events.
So, what will the world be like without dry and viscous
friction of all kinds? We will not be able to walk or move in any other way.
way. After all, while walking, the soles of our feet experience friction with the floor, and
without friction we will feel worse than we really do smooth ice in the most
slippery shoes.
Not a single item (including us)
will not be able to stay in one place. After all, everything that lies on the table, floor or
just the ground, held in place by static friction. What will happen? All bodies
will begin to move, trying to reach the lowest point. Almost on Earth
it is impossible to create a perfectly horizontal surface, even even
laboratory tables or machine beds have slopes of thousandths of a degree. But
in a world without friction, bodies will begin to move even on such planes.
It is clear that about transport and in general
there is no need to talk about the functioning of any mechanisms. Brake pads, pulleys and
belts, tires and the road - none of these will experience mutual friction, but
That means it won't work. And the cars themselves won’t exist - they’ll get out of them
all bolts and all nuts will be unscrewed, since they are held only thanks to
friction forces in the thread.
Suddenly the friction disappears, our houses are in
in the blink of an eye they will crumble - the mortar will no longer hold the bricks driven in
the nails will come out of the boards, because they are held there only by friction! Whole
Only welded or riveted metal structures will remain.
Without friction, many others will disappear
things that are familiar to us. It will not be possible to tie knots from ropes - they will
spread out. All woven materials will separate into separate threads, and the threads
disintegrate into the smallest fibers that make them up. Such a fate also awaits
metal and rope mesh.
Catastrophic changes await
nature - the very appearance of the Earth will change beyond recognition. Waves arising in
ocean, will never subside, and constant terrible winds will blow in the atmosphere
force - after all, there is no friction between the individual layers of water and air, which means nothing
does not prevent them from moving very quickly relative to each other. The rivers will flow out
their banks, and their waters will rush from high speed across the plains.
Mountains and hills will begin to crumble into
individual blocks and sand. Trees whose roots remain in the ground only because
friction will begin to uproot themselves and crawl in search of the lowest
points. Yes, a terrible picture will appear before our eyes: mountains, trees, huge
the blocks, and the soil itself, will crawl, mixing, until they find
balance point.
If the friction force disappears, then our
the planet will become a smooth ball, on which there will be no mountains, no depressions, no rivers,
no oceans - all this will break, flow out, mix and fall into one heap. A
strong, never-ending winds will pick up dust and carry it
over the planet. Life in such conditions is unlikely to be possible. .
Therefore, we cannot talk about friction as
about a harmful physical phenomenon. Yes, it is often simply vital to reduce
friction to a minimum, but often the maximum possible friction forces are needed, because
that friction is both an enemy and a friend.
Examples of friction force: beneficial and harmful
User deleted
If there were no friction, we would not be able to walk on the ground (remember how our feet slide on ice), we would not be able to ride a bicycle, car, or motorcycle (the wheels would spin in place), we would have nothing to wear (threads in fabric held by friction forces). If there were no friction, all the furniture in the room would be crowded into one corner, plates, cups and saucers would slide off the table, nails and screws would not stay in the wall, not a single thing would be able to be held in hands, etc. ., etc. To this we can add that if there had been no friction, it is unknown how the development of civilization on Earth would have proceeded - after all, our ancestors produced fire by friction.
Harmful: friction of grains of sand on metal inside the bearing, sliding friction of skates on ice should be as small as possible, friction of door lock mechanisms
shoes rub blisters,..
a perpetual motion machine is not created due to the force of friction, as wear occurs.
For ships at their speed, the greatest harm is caused not by shape resistance, but by the banal force of friction of water against the hull. And practically nothing can be done with it. Even the best color - the so-called “self-polishing” one, although it reduces it, is far from sufficient to reduce the friction force many times over.
Dasha Deryabina
The benefits and harms of friction
Of course, this is a fantasy, and it is full of lyrical simplifications. In life everything is a little different. But, in fact, despite the fact that there are obvious disadvantages of the friction force, which create a number of difficulties for us in life, it is obvious that without the existence of friction forces, there would be much more problems. So we need to talk about both the harm of friction forces and the benefits of the same friction forces.
Examples of the beneficial aspects of friction forces include the fact that we can walk on the ground, that our clothes do not fall apart, since the threads in the fabric are held in place thanks to the same friction forces, that by pouring sand on an icy road, we improve traction with the road in order to avoid accidents.
Well, the harm of friction force is the problem of moving large loads, the problem of wear of rubbing surfaces, as well as the impossibility of creating perpetual motion machine, since due to friction any movement sooner or later stops, requiring constant external influence.
People have learned to adapt and reduce or increase friction forces, depending on the need. These include wheels, lubrication, sharpening, and much more. There are a lot of examples, and it is obvious that it is impossible to say unequivocally: friction is good or bad. But it exists, and our task is to learn how to use it for human benefit.
In physics, we were asked to write a fairy tale about the dangers and benefits of friction... Explain what kind of fairy tale to write in physics?
Vladimir Lis
Fat from the belly and sides will disappear in just 3-4 days if you take it regularly...
Fat from the belly and sides will disappear in just 3-4 days if you take it regularly...
Soldatova V. M.
Physics teacher
MBOU " high school No. 19 SUIOP"
Stary Oskol
Lesson topic: “The benefits and harms of friction”
Lesson objectives.
Educational: expand and consolidate students’ knowledge about the force of friction, types of friction force.
Educational: to develop teamwork skills combined with student independence, to cultivate curiosity.
Developmental: teach students to apply knowledge in new situation, develop the ability to explain surrounding phenomena, skills in working with additional literature.
Equipment: presentation, dynamometer, sheet of paper, sheet of sandpaper, table-drawing, multimedia equipment.
During the classes.
The lesson begins with the teacher talking about the types of friction force, the magnitude and direction of the friction force, the dependence of the sliding friction force on the type of rubbing surfaces, and the mechanism of occurrence of the static friction force.
An excerpt from the fairy tale “Turnip” is heard (insert).
Teacher. Grandfather planted a turnip. The turnip grew very, very big. It was heavy, very heavy, it grew in all directions and squeezed the soil. That is why its tuber came into very close contact with the soil; the earth penetrated into all the smallest cracks and protrusions.
Grandfather went to pick turnips. He pulls and pulls, but he can’t pull it out. He lacks strength. The turnip rests, clings to the ground with irregularities and protrusions, and resists its movement. The soil particles stick to the turnip and prevent the turnip from moving relative to the ground.
While the grandfather is thinking about what’s going on, why can’t he pull out the turnip, you and I will remember the force of friction.
(Work with cards)
Assignment: designation, units of measurement and formula for finding the friction force.
Teacher. The grandfather called the grandmother, the grandmother called for the grandfather, the grandfather for the turnip, they pulled and pulled, they couldn’t pull it out, the thick, rounded root held tightly in the ground. The force of gravity presses him to the ground. No, and they can’t do it together.
Guys, let’s help them with our knowledge gained in physics lessons, answer the questions:
1)What is gravity called? frictional force?
2) What are the causes of friction?
3) What friction forces do you know?
Let's return to the fairy tale. The grandmother called her granddaughter. Granddaughter for grandmother, grandmother for grandfather, grandfather for turnip, they pull and pull, they cannot pull, the total force that arises along the surface of contact of the turnip with the ground is called the force of static friction.
Let's help them. To do this, we will conduct a laboratory experiment to determine the dependence of the friction force on the type of rubbing surfaces. To conduct the experiment, you must have a dynamometer, a sheet of paper, a sheet of sandpaper, and a wooden ruler.
During the laboratory experiment, we conclude: the force of sliding friction depends on the type of rubbing surfaces; if the surface of the turnip were smooth, then the turnip would be pulled out.
The granddaughter called Zhuchka. The bug rested its four paws on the ground. Friction also arises between the paws and the ground. This power helps the Bug in the same way as it helps a grandfather, grandmother and granddaughter. Without this strength, they would not have been able to resist, they would have slipped and slid along the ground.
A bug for a granddaughter, a granddaughter for a grandmother, a grandmother for a grandfather, a grandfather for a turnip, they can’t pull, pull, pull.
The turnip moved a little. The magnitude of these small movements is proportional to the applied force and depends on the properties of the soil itself, and the adhesion of the turnip to the ground leads to an increase in the elastic force of the soil. And the resulting elastic force of the soil is the static friction force. She doesn’t allow me to pull out the turnip in any way. From here, we conclude that the force of friction also causes harm.
A student reads a poem about the benefits of friction and its harms.
The bug called the cat. A cat for a bug, a bug for a granddaughter, a granddaughter for a grandmother, a grandmother for a grandfather, a grandfather for a turnip, they pull and pull, they can’t pull it out, even just a little, but still, the external force turned out to be less than the greatest value
The benefits and harms of bananas for women
The benefits and harms of pickled cucumbers
Municipal educational institution B. Tersenskaya secondary school, Urensky district, Nizhny Novgorod region Presentation On behalf of the student. Publishing house “Enlightenment”, 1975 I. Hypothesis. II. Goals. III. The nature of friction force. IV. Application of friction force in technology. V. Laws of friction. VI. Every cloud has a silver lining (harm and benefit have found their place). VII.How many people, so many opinions. VIII.Conclusion. The force of friction brings both harm and benefit. It is important that a person finds a worthy use for these extremes. I. Consider the nature of the friction force. II. Study its practical application. III. Draw a conclusion. Friction forces arise due to the existence of interaction forces between molecules and atoms of contacting bodies. The latter are caused by the interaction of electric charges possessed by the particles that make up the atoms. Friction force of rolling static sliding F, H The laws of friction were discovered in the XVIIX-VIII centuries. French scientists Amonton and Coulomb: 1. The force of friction is directly proportional to the force of normal pressure of a body on the surface on which it moves. 2. The friction force does not depend on the contact area between the rubbing surfaces. 3. The friction coefficient depends on the properties of the rubbing surfaces. 4. The friction force does not depend on the speed of the body. Dependence of friction force on normal pressure 2.5 2 1.5 1 0.5 0 0 1 2 N,H 3 Transport on skids and on air cushion ; Transport on rollers and wheels; Self-propelled wheeled carriages ;, machines and other technical devices. But! Man has learned to use both the pros and cons of friction. A survey was conducted among the residents of our village: what is the force of friction and what is its significance for human life and activity? 15% answered that they had studied this once, but forgot. 25% remember the types of friction, but find it difficult to talk about the meaning of friction force. 30% explained the importance of friction force for human life. 3% know everything about the force of friction. 10% were able to give examples of friction. 17% declined to answer. 15 25 30 10 17 3 Social survey on the topic 3% 17% 15% 10% 25% 30% To the question: “Is friction force harmful or beneficial,” they answered unequivocally, “Probably harm.” “There is a silver lining, and a good thing without a silver lining,” says the Russian proverb. Friction by its nature interferes with movement. But nevertheless, a person would not be able to move without the existence of the static friction force. The examples of practical use of friction given in this presentation provide an answer to the question I posed. The force of friction benefits humans.
Friction forces, accompanying us everywhere, play a huge role in our lives. True, we do not notice this in our everyday worries and most often strive reduce friction to a minimum.
Bearings, lubricants, streamlined shapes - all this and much more allows you to successfully combat various types friction. This takes a lot of effort and money, due to which an opinion has developed about the dangers of friction, that if friction suddenly disappeared, then a person would only benefit. But is it?
This is far from true, because friction is both our enemy and our ally. In some cases, the absence of friction can lead to big troubles (for example, car braking occurs only due to friction forces arising between the pads and the drum), and in some cases even minimal frictional forces have the most harmful effects (for example, in mechanical watches and delicate scientific instruments). However, to understand the full significance of friction, it is necessary to “turn it off” and monitor future events.
So, what would the world be like without dry and viscous friction of all kinds? We will not be able to walk or move in any other way. After all, while walking, the soles of our feet experience friction with the floor, and without friction we will feel worse than on the smoothest ice in the slipperiest shoes.
Not a single object (including us) can be in one place. After all, everything that lies on a table, floor or just the ground is held by static friction. What will happen? All bodies will begin to move, trying to reach the lowest point. On Earth it is almost impossible to create a perfectly horizontal surface, even level laboratory tables or machine beds have slopes in thousandths of a degree. But in a world without friction, bodies will begin to move even on such planes.
It is clear that there is no need to talk about transport and in general about the operation of any mechanisms. Brake pads, pulleys and belts, tires and the road - none of these will experience mutual friction, and therefore will not work. And the machines themselves will no longer exist - all the bolts will be unscrewed from them and all the nuts will be unscrewed, since they are held in place only due to the frictional forces in the threads.
If friction suddenly disappeared, our houses would crumble in the blink of an eye - the mortar would no longer hold the bricks, the driven nails would come out of the boards, because they are held there only by friction! Only welded or riveted metal structures will remain intact.
No friction Many other things familiar to us will also disappear. It will be impossible to tie knots from ropes - they will unravel. All woven materials will separate into individual threads, and the threads will disintegrate into the smallest fibers that make them up. The same fate awaits metal and rope nets.
Catastrophic changes await nature - the very appearance of the Earth will change beyond recognition. The waves arising in the ocean will never subside, and constant winds of terrible force will blow in the atmosphere - after all, there is no friction between the individual layers of water and air, which means that nothing prevents them from moving very quickly relative to each other. The rivers will overflow their banks, and their waters will rush at high speed across the plains.
Mountains and hills will begin to crumble into separate blocks and sand. Trees whose roots are kept in the ground only because of friction will begin to uproot themselves and crawl in search of the lowest point. Yes, a terrible picture will appear before our eyes: mountains, trees, huge boulders, and the soil itself will crawl, mixing, until they find a point of balance.
If the friction force disappears, then our planet will become a smooth ball, on which there will be no mountains, no depressions, no rivers, no oceans - all this will break, flow out, mix and fall into one heap. And strong winds that never subside for a minute will pick up dust and carry it over the planet. Life in such conditions is unlikely to be possible...
Therefore, we cannot talk about friction as a harmful physical phenomenon. Yes, it is often vital to reduce friction to a minimum, but often the maximum possible friction forces are also needed, because friction is both an enemy and a friend.
If you try to move a heavy closet full of things, then somehow it will immediately become clear that everything is not so simple, and something is clearly interfering with the good cause of putting things in order. And the obstacle to movement will be nothing more than work done by friction force, which is studied in the seventh grade physics course.
We encounter friction at every step. In the literal sense of the word. It would be more accurate to say that without friction we cannot even take a step, since it is the friction forces that keep our feet on the surface. Any of us knows what it is to walk on a very slippery surface - on ice, if this process can be called walking at all. That is, we immediately see the obvious advantages of friction force. However, before talking about the benefits or harms of friction forces, let us first consider what friction force is in physics.
What is friction force in physics?
The interaction that occurs at the point of contact of two bodies and prevents their relative motion is called friction. And the force that characterizes this interaction is called the friction force.
Types of friction: static friction
There are three types of friction: sliding friction, static friction and rolling friction. In our case, when we tried to move the cabinet, we huffed, pushed, and blushed, but did not move the cabinet an inch. What holds the cabinet in place? Static friction force. Now another example: if we put our hand on a notebook and move it along the table, then the notebook will move along with our hand, held by the same force of static friction. The static friction holds the nails driven into the wall, prevents shoelaces from untying spontaneously, and also holds our closet in place so that we, accidentally leaning our shoulders on it, do not run over our beloved cat, who suddenly lay down to take a nap in the peace and quiet between the closet and the wall.
Sliding friction
Let's go back to our proverbial closet. We finally realized that we wouldn’t be able to move it alone and called a neighbor for help. In the end, after scratching the entire floor, sweating, scaring the cat, but still not unloading things from the closet, we moved it to another corner. What did we find except clouds of dust and a piece of wall not covered with wallpaper? That when we applied a force exceeding the force of static friction, the cabinet not only moved from its place, but also (with our help, of course) continued to move further, to the place we needed. And the effort that had to be spent on moving it was approximately the same throughout the entire journey. IN in this case We were hampered by the force of sliding friction. The sliding friction force, like the static friction force, is directed in the direction opposite to the applied force.
What are the causes of friction forces? The first is surface roughness. This is well understood using the example of floor boards or the surface of the Earth. In the case of smoother surfaces, for example, ice or a roof covered with metal sheets, roughness is almost invisible, but this does not mean that they are not there. These roughness and irregularities cling to each other and interfere with movement. The second reason is intermolecular attraction, which acts at the points of contact of rubbing bodies. However, the second reason appears mainly only in the case of very well polished bodies. Basically, we are dealing with the first cause of friction forces. And in this case, to reduce the friction force, lubricant is often used. A layer of lubricant, most often liquid, separates the rubbing surfaces, and layers of liquid rub against each other, the friction force in which is several times less.
Rolling friction
In the case when a body does not slide on a surface, but rolls, the friction that arises at the point of contact is called rolling friction. The rolling wheel is slightly pressed into the road, and a small bump forms in front of it, which has to be overcome. This is what causes rolling friction. The harder the road, the less rolling friction. This is why driving on the highway is much easier than driving on sand. In the vast majority of cases, rolling friction is significantly less than sliding friction. That is why wheels, bearings, and so on are widely used.
Essay on the topic of friction force
In the seventh grade physics course, schoolchildren are given assignment to write an essay on the topic “Friction Force”. An example of an essay on this topic would be something like this:
“Suppose we decided to go to visit our grandmother by train during the holidays. And they don’t know that just at this time, suddenly, for no reason at all, the friction force disappeared. We wake up, get out of bed and fall, since there is no friction force between the floor and legs. We begin to put on our shoes and cannot tie the laces, which do not hold on due to the lack of friction. The stairs are generally difficult, the elevator does not work - it has been in the basement for a long time. Having counted absolutely all the steps with my tailbone and somehow crawled to the stop, we discovered a new problem: not a single bus stopped at the stop. We miraculously boarded the train, we thought how beautiful it is - it’s good here, less fuel is consumed, since friction losses are reduced to zero, we’ll get there faster. But here's the problem. There is no friction force between the wheels and rails, which means there is nothing for the train to push off from! So, in general, it’s not destiny to go to grandma without friction force.”
The benefits and harms of friction
Of course, this is a fantasy, and it is full of lyrical simplifications. In life everything is a little different. But, in fact, despite the fact that there are obvious disadvantages of the friction force, which create a number of difficulties for us in life, it is obvious that without the existence of friction forces, there would be much more problems. So we need to talk about both the harm of friction forces and the benefits of the same friction forces. Examples of useful aspects of friction forces you can say that we can walk on the ground, that our clothes do not fall apart, since the threads in the fabric are held in place thanks to the same frictional forces, that by pouring sand on an icy road, we improve traction in order to avoid an accident. well and harm from frictional forces is the problem of moving large loads, the problem of wear of rubbing surfaces, as well as the impossibility of creating a perpetual motion machine, since due to friction any movement sooner or later stops, requiring constant external influence.
People have learned to adapt and reduce or increase friction forces, depending on need. These include wheels, lubrication, sharpening, and much more. There are a lot of examples, and it is obvious that it is impossible to say unequivocally: friction is good or bad. But it exists, and our task is to learn how to use it for human benefit.
Why does friction occur, what does it affect, what does the force of friction depend on? And finally, is friction friend or foe?
What is friction force?
Having a little run up, you can dash along the icy path. But try doing it on regular asphalt. However, it’s not worth trying. Nothing will work out. The culprit of your failure will be a very large friction force. For the same reason, it is difficult to move a massive table or, say, a piano.
At the point of contact of two bodies, interaction always occurs, which prevents the movement of one body on the surface of another. It's called friction. And the magnitude of this interaction is the force of friction.
Types of friction forces
Let's imagine that you need to move a heavy cabinet. Your strength is clearly not enough. Let's increase the “shearing” force. At the same time, the friction force increases peace. And it is directed to the side opposite movement closet Finally, the “shearing” force “wins” and the cabinet moves away. Now the friction force comes into its own slip. But it is less than the static friction force and it is much easier to move the cabinet further.
Of course, you had to watch how 2-3 people rolled to the side heavy car with the engine suddenly stalled. The people pushing the car are not strongmen, the friction force is just acting on the wheels of the car rolling. This type of friction occurs when one body rolls over the surface of another. A ball, a round or faceted pencil, the wheels of a train, etc. can roll. This type of friction is much less than the sliding friction force. Therefore, it is very easy to move heavy furniture if it is equipped with wheels.
But, in this case, the friction force is directed against the movement of the body, therefore, it reduces the speed of the body. If it were not for its “harmful nature,” having accelerated on a bicycle or roller skates, you could enjoy the ride indefinitely. For the same reason, a car with the engine turned off will move by inertia for some time and then stop.
So, remember, there are 3 types of friction forces:
- sliding friction;
- rolling friction;
- static friction.
The rate at which speed changes is called acceleration. But, since the friction force slows down the movement, this acceleration will have a minus sign. It would be correct to say Under the influence of friction, a body moves with deceleration. It is to reduce friction that skiers lubricate their skis with special ointments to increase speed when moving. Rinks used by speed skaters or figure skaters are periodically watered and cleaned, also to reduce friction.
What is the nature of friction
If we consider smooth surface polished table or ice through a magnifying glass, then you will see tiny roughnesses, to which the body clings, sliding or rolling along its surface. After all, a body moving along these surfaces also has similar protrusions.
At the points of contact, the molecules come so close that they begin to attract each other. But the body continues to move, the atoms move away from each other, the bonds between them break. This causes the atoms freed from attraction to vibrate. Approximately the way a spring freed from tension oscillates. We perceive these vibrations of molecules as heating. That's why friction is always accompanied by an increase in the temperature of the contacting surfaces.
This means that there are two reasons causing this phenomenon:
- irregularities on the surface of contacting bodies;
- forces of intermolecular attraction.
What does friction force depend on?
You've probably noticed the sudden braking of a sled when it slides onto a sandy area. And one more interesting observation: when there is one person on the sled, they will go one way down the hill. And if two friends slide together, the sled will stop faster. Therefore, the friction force is:
- depends on the material of the contacting surfaces;
- in addition, friction increases with increasing body weight;
- acts in the direction opposite to the movement.
The wonderful science of physics is also good because many dependencies can be expressed not only in words, but also in the form of special signs (formulas). For the friction force it looks like this:
Ftr = µN
Ftr - friction force.
µ - friction coefficient, which reflects the dependence of the friction force on the material and the cleanliness of its processing. Let's say, if metal rolls on metal µ = 0.18, if you skate on ice µ = 0.02 (friction coefficient is always less than one);
N is the force acting on the support (support reaction force). If the body is on a horizontal surface, this force is equal to the weight of the body. For an inclined plane it is less weight and depends on the angle of inclination. The steeper the slide, the easier it is to slide down and the longer you can ride.
And, by calculating the static friction force of the cabinet using this formula, we will find out what force needs to be applied to move it from its place.
Work of friction force
If a force acts on a body, under the influence of which the body moves, then work is always done. The work of the friction force has its own characteristics: after all, it does not cause movement, but prevents it. Therefore, the work it does is will always be negative, i.e. with a minus sign, no matter which direction the body moves.
Is friction friend or foe?
Friction forces accompany us everywhere, bringing tangible harm and... enormous benefit. No friction We won’t be able to take a single step. After all, it is friction that helps us push off the ground when walking. Now it’s clear why slippery roads are sprinkled with sand or ash in winter so that no one falls on them. Some inventors and innovators even came up with the idea of gluing pieces of sandpaper to the soles of winter boots and boots just to increase the friction force.
And at the same time, sometimes friction causes significant harm. People have learned to reduce and increase friction, deriving enormous benefits from it. For example, wheels were invented to drag heavy loads, replacing sliding friction with rolling, which is significantly less than sliding friction.
Because a rolling body does not have to catch many small surface irregularities, as when bodies slide. Then the wheels were equipped with tires with a deep pattern (treads).
Have you noticed that all the tires are rubber and black?
It turns out that rubber holds the wheels well on the road, and the coal added to the rubber gives it a black color and the necessary rigidity and strength. In addition, in case of accidents on the road, it allows you to measure the braking distance. After all, when braking, the tires leave a clear black mark.
If necessary, reduce friction, use lubricating oils and dry graphite lubricant. A remarkable invention was the creation different types ball bearings. They are used in a wide variety of mechanisms, from bicycles to the latest aircraft.
Is there friction in liquids?
When a body is stationary in water, friction with the water does not occur. But as soon as it starts moving, friction arises, i.e. Water resists the movement of any bodies in it.
This means that the shore, creating friction, “slows down” the water. And, since the friction of water on the shore reduces its speed, you should not swim into the middle of the river, because the current there is much stronger. Fish and sea animals are shaped in such a way that the friction of their bodies on the water is minimal. Designers give the same streamlining to submarines.
The force of friction constantly accompanies us throughout our lives, just like the force of gravity. In some places it creates inconvenience for us, and in others we cannot do without it. But be that as it may, it exists, and our task is to learn to use physical laws so that our life becomes more convenient and comfortable.
