Research work “Friction force and its beneficial properties. Friction Types of friction forces What does the friction force depend on? Friction in mechanisms and machines Interesting facts

If you suddenly want to move a heavy object, it will become obvious that something is blocking you. The friction force will interfere with the movement. We encounter friction at every step. In the literal sense of the word. More precisely, we cannot take a step without friction, since friction forces keep our feet on the surface.

Friction is a consequence of many reasons, but two main ones are. Firstly, the surfaces of bodies are uneven, and the jagged edges of one surface cling to the roughness of another. This is the so-called geometric friction. Secondly, the rubbing bodies are in very close contact with each other, and their movement is influenced by the interaction of molecules (molecular friction).

There are three types of friction: static friction, sliding friction, and rolling friction.

Static friction force - a force that arises between two contacting bodies and prevents the occurrence of relative motion. This force must be overcome in order to set two contacting bodies in motion relative to each other.

Sliding friction force - the force that arises between bodies in contact during their relative motion.

Rolling friction force - call the resistance that occurs when one body rolls over the surface of another.

Obviously, any phenomenon has pros and cons. And it’s stupid to say that friction is not needed, for example, because parts wear out. But how would we go?

Below I will try to write the main pros and cons, although I know in advance that this is difficult to do.

Without friction, objects would slip out of our hands, and we would not be able to walk on the ground, we would only slide (I dare say, like snails).
Friction is the main, sometimes the only force that can stop a moving body.
Friction prevents the threads from straightening out and the fabric from falling apart into individual threads.
Getting fire in a primitive way.

Friction is a factor that transfers part of the energy imparted to the system (for example, vibration) into heat until all this energy is used up. For example, when a swing swings, it will sooner or later stop if no action is taken on it.
Static friction is the main obstacle to moving a heavy object from its place.
Friction causes a decrease in the performance of parts and assemblies of mechanisms, deterioration in the quality of surfaces and, as a consequence, a sharp decrease in efficiency, in some cases, failure of parts and assemblies or even the entire mechanism as a whole.

I realize that this division is purely everyday. Any plus can be turned into a minus, and a minus into a plus. I can say for sure that we definitely cannot do without friction. We can say that it hinders us, but do not forget how many times it has helped. We just don't think about it. And, probably, it would be worth it, although this is a philosophical question.

If you think the list is incomplete and you would like to add to it, please provide your suggestions in the comments.

Did you know that back in 1500, the brilliant Leonardo da Vinci was very interested in what the force of friction depends on and what it represents? The strange experiments that he conducted caused considerable surprise among his students, and what else could be expected from people who see a talented scientist dragging a rope across the floor, either unwound to its full length, or tightly coiled. These and other similar experiments allowed him a little later (in 1519) to conclude: the friction force that appears when one body comes into contact with the surface of another directly depends on the load (pressure force), does not depend on the interaction area and is directed in the opposite direction from the movement side.

Opening the formula

180 years passed, and Leonardo's model was rediscovered by G. Amonton, and in 1781, S. O. Coulomb gave it its final formulation in his works. The merit of these two scientists is that they introduced such a physical constant as the friction coefficient, thereby making it possible to derive a formula that can be used to calculate what the friction force is equal to for a specific pair of interacting materials. Until now it is this expression

F t = k t x P, where

P is the pressing force (load), and k t is the friction coefficient, which migrates from year to year to various textbooks and manuals on physics, and the coefficients themselves have long been calculated and are contained in standard engineering reference books. It would seem that this phenomenon had finally become completely clear, but that was not the case.

New nuances

In the 19th century, scientists became convinced that the formulation proposed by Amonton and Coulomb was not universal and absolutely correct, and the friction force depended not only on the coefficients and the applied load. In addition, there is a third factor - the quality of surface treatment. Depending on whether it is smooth or rough, the friction force will take on a different value. In principle, this is quite logical: moving a sliding object is much easier compared to moving an object with an uneven surface. And at the end of the 19th century, new achievements appeared in the study of viscosity, and it became clear how the friction force acts in liquids. And although lubrication of rubbing surfaces was used from the very beginning of technology, it was only in 1886, thanks to O. Reynolds, that a coherent theory dedicated to lubrication appeared.
So, if there is enough of it, and there is no direct contact between two objects, the friction force depends only on its hydrodynamics. And if there is not enough lubricant, then all three mechanisms are activated: the Coulomb force, the viscous resistance force and the force that prevents it from moving away. Do you think this theory has put an end to the study of this phenomenon? That's right, no. At the threshold of the twentieth century, it turned out that at low speeds in the absence of lubrication, a stripe effect occurs. Its essence is that when there is no lubrication, the resistance force does not immediately decrease from the starting force to the level of the coulomb force, but falls gradually as the speed increases. In the twentieth century, further research in this area brought so much new information that it needed to be somehow systematized. As a result, a whole science appeared - tribology, which studies how the force of friction acts in nature. In the USA alone, the number of scientists working in this field has exceeded one thousand people, and more than 700 articles are published annually on this topic around the world. I wonder what else interesting things scientists will be able to discover? Wait and see!

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! Thus, by using sand to reinforce the space between the slippery ice and the 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 are again clear 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 “shoe” their iron horses in special “winter tires.” Otherwise, without useful friction force, 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 friction force, 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, 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 at this time. This means that it should be reduced: make the contacting surfaces smoother and slippery. 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 or 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 as somewhere it creates inconvenience for us, and somewhere 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.

There are many physical phenomena in the world around us: thunder and lightning, rain and hail, electric current, friction... Our report today is dedicated to friction. 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 in the direction opposite to the movement of the cabinet. 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 moving the cabinet further is much easier.

You, of course, have had to watch how 2-3 people roll away a heavy car with a suddenly stalled engine. 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.

What is the nature of friction

If you examine the smooth surface of a polished table or ice through a magnifying glass, you will see tiny roughnesses to which a body sliding or rolling along its surface clings. 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 = kN Where:

Ftr - friction force.

k - 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 k=0.18, if you skate on ice k=0.02 (the friction coefficient is always less than one);

N is the force acting on the support. 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 way the body moves.

Is friction friend or foe?

Friction forces accompany us everywhere, bringing tangible harm and... enormous benefit. Let's imagine that friction has disappeared. An astonished observer would see how mountains collapse, trees are uprooted from the ground by themselves, hurricane winds and sea waves endlessly dominate the earth. All the bodies are sliding down somewhere, the transport is falling apart into separate parts, since the bolts do not fulfill their role without friction, an invisible monster would have untied all the laces and knots, the furniture, not held by friction forces, has slid into the lowest corner of the room.

Let's try to escape, to escape from this chaos, but without 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 covered with sand in winter...

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 of different types of 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 against the water is minimal.

Designers give the same streamlining to submarines.

Our acquaintance with other natural phenomena will continue. See you again, friends!

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The science

European scientists have provided a modern explanation for the origin of sliding friction between solid objects. Despite the fact that friction is one of the fundamental phenomena of modern applied physics, This phenomenon has not stopped being studied for many centuries.. Until the present day, it was believed that mechanical wear resistance and the presence (or absence) of liquid lubrication are among the main factors influencing friction, but the fundamental causes of sliding friction remained unknown.

Dr. Lacey Makkonen, a senior researcher at the Technical Research Center in Finland, presented his own explanation of the origin of sliding friction between solid objects. His theory fully confirms the fact that the magnitude of friction also depends on the so-called surface energy of the materials in question. Moreover, friction has a significant effect on many phenomena that we encounter every time (such as, for example, the absorption of energy).

Makkonen's new thermodynamic model is the first of its kind to quantify the coefficient of friction of materials by taking into account the surface energy of materials. The model, in fact, shows that friction occurs when materials come into contact at the nanoscale level, resulting from the formation of new bonds at the atomic level. This theory complements the explanation of the origin of friction force and the presence of frictional heating during dry friction. It can also be used to more accurately calculate the friction coefficients of combinations of different materials.

The constructed model also makes it possible to more accurately control friction processes by selecting a specific surface of materials or through the use of lubricating layers, taking into account the presence of surface energy between them. It is noteworthy that this theory confirms the opinions of many physicists that in the well-known tables with friction coefficients presented in them for various materials (especially for homogeneous ones) there are noticeable inaccuracies.