The force of friction is encountered literally at every step. But do people know why it is needed? What is the harm and benefit of friction force? Let's try to figure it out.
Foreword
Several forces act on terrestrial objects, which are closely interconnected and affect the vital activity of bodies. First of all, it is gravity, elasticity (internal resistance of bodies in response to the displacement of their molecules) and support reactions. But there is also a very important physical quantity called the friction force. It, unlike the force of gravity and elasticity, does not depend on the location of the bodies. When studying it, other laws apply: the coefficient of sliding friction and the reaction force of the support. 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 applied to the cabinet? And this is hindered by nothing more than the force of friction, the principle of which is studied at school. The course of physics for grade 7 talks in detail about this phenomenon.
Ambiguous question
What is the harm and benefit 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 friction force has obvious disadvantages that create a number of difficulties in life, it is clear that without it there would be much more problems. Therefore, this value has its advantages and disadvantages.
Negative Examples
Among the examples of the harm of this force, one of the first places is the problem of moving heavy loads, the rapid wear of favorite things, and the impossibility of creating a perpetual motion machine, because due to friction, any movement sooner or later stops, requiring third-party intervention.
Positive points
Among the examples of the usefulness of this power is that we can safely walk on the ground without slipping at every step, our clothes are firmly seated and do not instantly become unusable, since the threads of the fabric are held by friction. In addition, people use the principle of this force by sprinkling slippery roads, due to which it is possible to avoid many accidents and injuries.
conclusions
Mankind has learned to interact with this physical quantity, increasing and decreasing it depending on the goals set. Our immediate task is to try to use it as efficiently as possible.
What is under our feet?
People encounter it very often. The benefit of friction is that we would not even be able to take a step without this physical quantity. It is she who keeps our shoes on the surface where we step. Each of us has walked on very slippery surfaces, for example, on ice, and knows firsthand that it is very difficult. Why is this happening? Before we talk about the harm and benefits of friction force, let's define what it is.
The essence of the concept
The force of friction 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 - rest, sliding and rolling.
Causes
The first reason is the constant surface roughness. It is this indicator that affects what kind of friction force will take place. If we are talking about smooth surfaces, such as a metal-plated 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 force of sliding friction will act. But if we talk about a cabinet standing on a carpet, then here the roughness of the two objects will significantly impede mutual movement. The second reason is the electromagnetic molecular repulsion that occurs at the point of contact between objects.
Friction of rest
What happens when we try to move a closet, but we cannot move it even a centimeter. What keeps an object in one place? This is the static friction force. The fact is that the applied efforts are compensated by the dry friction force that occurs between the cabinet and the floor.
Harm and benefit of static friction force
It is the static friction force that does not allow the laces on our shoes to untie on their own, the nail that we have just driven into the wall to fall out, and keeps the closet in place. Without it, it would be impossible for people, animals, or cars to move on the earth's surface. Friction damage is also present. It happens on a fairly global scale, for example, the static friction force can lead to deformation of ship plating.
Scientific rationale
In order to move the cabinet, it is necessary to apply a force to it that will overcome friction. That is, as long as the applied force is less than the friction force, the furniture will remain in place. In addition to these factors, there is also the reaction force of the support, which is directed perpendicular to the plane. It depends on the material from which the floor is made (here, the elastic force is also involved). There is also a coefficient of friction, depending on what the two surfaces that interact with each other consist of. Therefore, the friction force acting on the cabinet is equal to the coefficient of friction, 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 closet. What have we discovered? That after we applied a force that exceeded the static friction force, the cabinet not only shifted, but also continued to move in the necessary direction for some time, of course, with our help. And the effort spent was about the same throughout the entire journey. In this case, we were prevented by the sliding friction force directed in the opposite direction from the applied action. It is worth noting that its resistance is much lower than that of the static friction force. To reduce this figure, if necessary, apply various lubricants.
Rolling friction force
If we remember that someday we will have to move the cabinet back, we 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 on the surface. The rolling wheels will be pressed into the carpet a little, forming a tubercle that we will need to overcome. This determines the force of rolling friction. 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 parquet surface is harder than the carpet surface. For the same reason, it is much easier for cyclists to ride on a highway than on a fine sand beach.
The harm and benefits of friction force
Not going - just going
Because it's icy
But it falls great!
Why isn't anyone happy?
Such a naive nursery rhyme at first glance - and how much it contains, if you look at it from physical point vision! After all, it is precisely in it that the system of a contradictory attitude to the notorious force of friction is contained. This constant battle, where two concepts compete with each other - the harm and the benefits of the force 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.
Remember the story of Nikolai Nosov about the ice slide that the guys built in the yard? And when they all left for dinner, the one who did not participate in the construction came out. He tried to climb on it, but only hurt himself, but he could not climb. And the kid guessed to sprinkle sand on the ice - it became very convenient to climb to the very top even on ice! Thus, by increasing the force of friction between slippery ice and the sole, the boy realized that the use of friction allows you to overcome obstacles.
But after lunch, the kids came out with ice cubes to ride their slide to their heart's content. But it wasn’t there: the sled does not go on the sand! For them, this situation turned the other way, showing the harm of friction.
We observe similar cases in winter, when the boys roll out ice paths and rush along them with a run, covering the distance in a matter of minutes! And then elderly people hobble, slip on the snow-covered rolls and fall, breaking their arms and legs. Here you go again illustrative examples, where in the same case both the harm and the benefit of the friction force coexist.
It is to reduce the friction force that skiers lubricate their skis with special ointments in order to increase speed when moving. Skating rinks, where skaters or figure skaters are engaged, are periodically watered and cleaned - also to reduce friction. And footpaths, on the contrary, are sprinkled with sand or ash so that no one falls on them. Some 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 the wheels of cars. It's no secret that with the onset of winter, drivers "shoe" their iron horses in a special winter tires". Otherwise, without useful friction force increases braking distances, the car skids when cornering, it uses, and often the driver does not manage well. And how the accident ends, everyone knows for himself.
Something we are all about winter, but about ice, but about falling. But are there other moments in everyday life where you can clearly see how the harm and benefit of the force of friction compete with each other? Of course have! They are everywhere. Even in our room.
Here, for example, is a huge and heavy wardrobe. It stands to itself, as if rooted to the spot, and does not move. And if the force of friction suddenly disappeared, what could happen then? And this hulk would have gone from the lightest push around the room! And it is still unknown if we could manage to dodge it. 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, take it! Three - four, tensed up! Only everything turns out to be useless: the heavier the object, the stronger the friction force holds on to it. Terrible, nasty force!
Again they compete with each other - the harm and benefit of the force of friction. No competition needed! You just need to know physical laws well and be able to extract practical benefits from this knowledge. Not needed in this moment friction force? So, it should be reduced: to make the contact surfaces smoother, slippery. For this, someone advises smearing the floor with soap or oil, someone puts a wet rag under the legs of a heavy object. And now - one - two - and you're done! Moved quite easily a sort of colossus from its place.
The force of friction constantly accompanies us throughout life, just like the force of gravity. Somewhere it creates inconvenience for us, but somewhere it is impossible to do without it. But be that as it may, it exists, and our task is to learn how to use physical laws in such a way that our life becomes more convenient and comfortable.
The force of friction is encountered literally at every step. But do people know why it is needed? What is the harm and benefit of friction force? Let's try to figure it out.
Foreword
Several forces act on terrestrial objects, which are closely interconnected and affect the vital activity of bodies. First of all, it is gravity, elasticity (internal resistance of bodies in response to the displacement of their molecules) and support reactions. But there is also a very important physical quantity called the friction force. It, unlike the force of gravity and elasticity, does not depend on the location of the bodies. When studying it, other laws apply: the coefficient of sliding friction and the reaction force of the support. 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 applied to the cabinet? And this is hindered by nothing more than the force of friction, the principle of which is studied at school. The course of physics for grade 7 talks in detail about this phenomenon.
What is under our feet?
People encounter it very often. The benefit of friction is that we would not even be able to take a step without this physical quantity. It is she who keeps our shoes on the surface where we step. Each of us has walked on very slippery surfaces, for example, on ice, and knows firsthand that it is very difficult. Why is this happening? Before we talk about the harm and benefits of friction force, let's define what it is.
The essence of the concept
The force of friction 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 - rest, sliding and rolling.
Causes
The first reason is the constant surface roughness. It is this indicator that affects what kind of friction force will take place. If we are talking about smooth surfaces, such as a metal-plated 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 force of sliding friction will act. But if we talk about a cabinet standing on a carpet, then here the roughness of the two objects will significantly impede mutual movement. The second reason is the electromagnetic molecular repulsion that occurs at the point of contact between objects.
Friction of rest
What happens when we try to move a closet, but we cannot move it even a centimeter. What keeps an object in one place? This is the static friction force. The fact is that the applied efforts are compensated by the dry friction force that occurs between the cabinet and the floor.
Harm and benefit of static friction force
Rolling friction force
If we remember that someday we will have to move the cabinet back, we 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 on the surface. The rolling wheels will be pressed into the carpet a little, forming a tubercle that we will need to overcome. This determines the force of rolling friction. 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 parquet surface is harder than the carpet surface. For the same reason, it is much easier for cyclists to ride on a highway than on a fine sand beach.
Ambiguous question
What is the harm and benefit 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 friction force has obvious disadvantages that create a number of difficulties in life, it is clear that without it there would be much more problems. Therefore, this value has its advantages and disadvantages.
Negative Examples
Among the examples of the harm of this force, one of the first places is the problem of moving heavy loads, the rapid wear of favorite things, and the impossibility of creating a perpetual motion machine, because due to friction, any movement sooner or later stops, requiring third-party intervention.
Positive points
Among the examples of the usefulness of this power is that we can safely walk on the ground without slipping at every step, our clothes are firmly seated and do not instantly become unusable, since the threads of the fabric are held by friction. In addition, people use the principle of this force to sprinkle slippery roads, which avoids many accidents and injuries.
conclusions
Mankind has learned to interact with this physical quantity, increasing and decreasing it depending on the goals set. Our immediate task is to try to use it as efficiently as possible.
Friction forces, accompanying us everywhere, play a huge role in our life. True, we do not notice this behind everyday worries and most often strive to reduce friction to a minimum.
Bearings, lubricants, streamlined shapes - all this and much more allows you to successfully fight against various types friction. This takes a lot of effort and money, thanks to which there was an opinion about the dangers of friction, that if friction suddenly disappeared, then a person would only win. But is it?
Far from it, friction is both our enemy and our ally. In some cases, the absence of friction threatens with big troubles (for example, braking of cars occurs only due to friction forces arising between the pads and the drum), and in some cases even minimal friction forces have the most harmful effect(for example, in mechanical watches and thin scientific instruments). However, in order to understand the full significance of friction, it is necessary to “turn it off” and follow 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 we really are. smooth ice in the slipperiest shoes.
Not a single object (including us) can be in one place. After all, everything that lies on the table, floor or just the ground is held by the friction of rest. And what will happen? All bodies will start moving, trying to reach the lowest point. On Earth, it is almost impossible to create a perfectly horizontal surface, even flat laboratory tables or machine beds. have biases in thousandths of a degree. But in a world without friction, bodies will 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 road - none of this will experience mutual friction, which means it will not work. Yes, and the machines themselves will not be - all the bolts will be unscrewed from them and all the nuts will be unscrewed, since they are held only due to the forces of friction in the thread.
Suddenly disappear friction, our houses will crumble in the blink of an eye - the mortar will no longer hold bricks, driven nails will come out of the boards, because they are held there only due to friction! Only welded or riveted metal structures will remain intact.
Friction free many other familiar things will also disappear. It will not be possible to knit knots from the ropes - they will spread. All woven materials will disperse into separate threads, and the threads will fall apart into their smallest fibers. Such a fate also awaits metal and rope nets.
Catastrophic changes await nature - the very appearance of the Earth will change beyond recognition. The waves that arise 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. Rivers will overflow their banks and their waters will rush with high speed across the plains.
Mountains and hills will begin to crumble into separate blocks and sand. Trees whose roots are only held in the ground by friction will themselves begin to uproot 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 force of friction disappears, then our planet will become a smooth ball, on which there will be no mountains, no hollows, no rivers, no oceans - all this will break, flow out, mix up and fall into one heap. And strong, never abating winds will pick up dust and carry it over the planet. Life in such conditions is unlikely to be possible ...
Therefore, one cannot speak of friction as a harmful physical phenomenon. Yes, it is often vital to reduce friction to a minimum, but often the maximum possible frictional forces are also needed, because friction is both an enemy and a friend.
Friction is not always a bad thing. significant, and sometimes friction is simply necessary.
The Benefits of Friction - Examples
Once, a car was driving along the highway, loaded with three-meter rails. The rails protruded through the open tailgate. From the side it was noticeable that the truck was moving somehow uncertainly, roaring from side to side as if the driver was unable to cope with the steering. Here the car suddenly switched to left side road, the driver applied the brakes, the car leveled off and returned to the right side. But as soon as the driver increased the speed again, the car again began to wag to the right, to the left; the driver - on the brake, but, apparently, did not have time, and the truck buried itself in a ditch. The ditch was shallow. There was no serious accident. The driver turned on the stalled engine and in reverse got out on the highway. Then he stopped the car on the side of the road and began to look around - why did the car stop listening to the steering wheel? He checked steering- everything was OK; I went to inspect the cargo ... Suddenly, throwing off his jacket, he began to shift the rails. He guessed what it was. From the shaking, the rails slid back, and the front of the car began to rise. A little more - and the car would be "on its hind legs". The front wheels rolled, barely touching the ground. With each push, they completely lost traction with the ground. The friction between the front wheels and the road has become negligible; that's why the car lost control. The reason was in lack of friction. Friction often plays very important role, (more details: ). If the friction of the wheels on the rails is low on the locomotive, the wheels will begin to slip and the locomotive will not be able to move the train. Out of habit, it is difficult to walk quickly on a smooth, waxed parquet floor - the legs slip and do not provide the necessary support.The road turns the car
The driver, turning the steering wheel of the car, thereby causes his front wheels to turn. They are no longer along the road, but slightly sideways. The car, by inertia, tends to continue moving in the same direction, but the front wheels have turned and meet significant resistance from the road. Friction force the road turns the whole car in the direction in which the driver turns it.Water resistance force
Airplanes, steamships and simple boats also use the force of friction and water resistance force or air when they need to change the direction of their movement. For this they have a steering wheel. While the boat is moving straight, its rudder is in motion and encounters almost no resistance from the water: the jets easily flow around it. But as soon as the steering wheel turns to the side, water jets begin to run into one of its planes - significant water resistance, and its pressure pushes the rudder, and with it the stern of the boat, in the opposite direction to the rudder. The bow of the boat is heading in the same direction as the rudder is turned. On large ships, the forces generated by turning the rudder are so great that a person is not able to hold the steering wheel in his hands. Help comes Steam engine or Electrical engine. On large ships, special steering machines are installed that turn the steering wheel, and here, too, a person evaluates the benefits of variousIf 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 deed of putting things in order.
- And the traffic will be hindered by nothing more than friction work, 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 correct to say that without friction we cannot even take a step, since it is the forces of friction that keep our feet on the surface.
Any of us knows what it is like 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 the friction force. However, before talking about the benefits or harms of friction forces, let's first consider what the friction force is in physics.
Friction force in physics and its types
The interaction that occurs at the point of contact of two bodies and prevents them relative motion is called friction. And the force that characterizes this interaction is called the friction force.
- There are three types of friction: sliding friction, static friction and rolling friction.
Friction of rest
In our case, when we tried to move the cabinet, we puffed, pushed, blushed, but did not move the cabinet an inch. What holds the closet in place? The force of static friction. 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 static friction force.
Friction of rest keeps nails driven into the wall, prevents the shoelaces from spontaneously untying, and also keeps our closet in place so that we, accidentally leaning on it with our shoulder, do not crush our beloved cat, who suddenly lay down to take a nap in peace and quiet between the closet and the wall.
Sliding friction
Let's return to our notorious closet. We finally realized that we would not be able to move it alone and called for help from a neighbor. In the end, having scratched the entire floor, sweating, frightening the cat, but without unloading things from the closet, we moved it to another corner.
What did we find, except for clouds of dust and a piece of wall not pasted over with wallpaper? That when we applied a force exceeding the static friction force, the cabinet not only moved, but (with our help, of course) continued to move on, to the place we needed. And the efforts that had to be expended on its movement were approximately the same throughout the entire journey.
- IN this case bothered us sliding friction force. The force of sliding friction, like the force of static friction, is directed in the direction opposite to the applied force.
rolling friction
In the case when the body does not slide on the surface, but rolls, then the friction that occurs 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. That is why driving on the highway is much easier than on the sand. Rolling friction is in most cases significantly less than sliding friction. That is why wheels, bearings and so on are widely used.
Reasons for the emergence of friction forces
First is the surface roughness. This is well understood on the example of floorboards or the surface of the Earth. In the case of smoother surfaces, such as ice or a roof covered with metal sheets, the roughness is almost invisible, but this does not mean that they are not there. These roughnesses and irregularities cling to each other and interfere with movement.
The second reason- this 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, in order 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 many times less.
Composition on the topic "The force of friction"
In the seventh grade physics course, schoolchildren are given task to write an essay on the topic "The force of friction." An example of an essay on this topic is something like this fantasy:
“Let's say we decided to go on vacation to visit my grandmother by train. And they are not aware that just at that time, suddenly, for no apparent reason, the friction force disappeared. We woke up, get out of bed and fall, as there is no friction force between the floor and the legs.
We start to put on shoes, and we cannot tie laces that do not hold due to the lack of friction. The stairs are generally tight, the elevator does not work - it has been lying in the basement for a long time. Having counted absolutely all the steps with the coccyx and somehow crawled to the stop, we discover a new misfortune: not a single bus stopped at the stop.
Miraculously, we boarded the train, we think, what a beauty - it’s good here, less fuel is consumed, since friction losses are reduced to zero, we’ll get there faster. But here's the trouble: there is no friction force between the wheels and the rails, and, therefore, there is nothing to push off the train from! So, in general, somehow it’s not fate to go to my grandmother without friction.”
The benefits and harms of friction force
Of course, this is a fantasy, and it is full of lyrical simplifications. Life 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 dangers of friction forces and the benefits of all the same friction forces.
Examples of useful sides of friction forces it can be called that we can walk on the ground, that our clothes do not fall apart, since the threads in the fabric are held by the same friction forces that by pouring sand on an icy road, we improve traction in order to avoid an accident.
well and damage to the force of friction is the problem of displacement big cargo, the problem of wear of rubbing surfaces, as well as the impossibility of creating perpetual motion machine, since due to friction, any movement stops sooner or later, requiring constant external influence.
People have learned to adapt decrease or increase the force of friction, depending on the need. These are wheels, and lubrication, and sharpening, and much more. There are many 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 the benefit of man.
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