Urgent!!! What is the essence of the roughness of friction in physics?

The essence can only be said to be electromagnetic. No one can fully understand how it works, because there are too many molecules and the effects are too complex. And what you are talking about is all obtained from experiments in classical physics, a bit of an empirical component, of course, from a macroscopic point of view.

You want to know exactly what it is and why I can understand it, but any law of physics is just an approximation of the laws of nature, and you can't think of those laws as strict as the definition in mathematics. So all you've learned is to solve real-world problems on a macro level. As for what your teacher said, it is also a practical problem, it is more complicated, maybe no one knows why, he said that it is related to the area, and I also said that it is because it is rolled up, and the nature of the contact area has changed.

The teacher is wrong, the example given is inappropriate, the most essential relationship between the friction factor of an object is the material of the object itself. Once two objects are separated, the forces between the molecules or between the atoms are negligible. So roughness doesn't have much to do with the intermolecular forces.

However, the formula of driven friction does not mention the force area, so it has nothing to do with the contact area.

The roughness has a lot to do with the contact surface of the object. Let's take an example, you ride your bike onto the road and it feels flat and you keep going. However, once you walk the stone road in the mountains, although it is also straight, it is very difficult for you to ride.

That's because although there are gaps in the gravel on the road, this space does not affect your bike. However, the gap between the rocks in the mountains greatly affects your bicycle, so the friction factor of the road is small, and the friction factor of the road in the mountains is large. If we make these two paths smaller, we will be the surface of the object.

Some objects have very smooth surfaces, such as glass. Some objects have very rough surfaces, such as wood. From a physical point of view, when we say that there is friction in an object, it is actually just these small bumps and bumps between two objects that hinder each other.

Different objects have different levels of smoothness due to the different ways in which their molecules or atoms are arranged.

Let's analyze why the example given by the teacher is inappropriate. Because the force per unit area is very small, and the gap between the hairs of the blanket is very large, the obstructive force (friction factor) is large, so it is difficult to drag. And when rolled up, the force per unit area is very large.

In this way, the gap between the hairs is correspondingly reduced, so the blocking force (friction factor) is small. So the blanket is rolled up with less friction.

Friction is the positive pressure friction factor, the friction factor is the roughness of the object, it is the macroscopic thing, how to get the molecular angle.

Sweat! Are you in junior high school?

Friction is the force that hinders the relative motion of two objects on the contact surface of two objects when they are in relative motion or have a tendency to move relative to each other.

There are three types of frictional force, sliding friction, rolling friction and static friction. Sliding friction is the force generated when two objects in contact are in relative motion and sliding, the direction is opposite to the direction of motion, and the magnitude is determined by the roughness of the contact surface and the pressure on the contact surface, and other factors such as the speed of sliding cannot affect its size. Static friction is the friction between two objects that are in contact but have not yet moved in relative motion, for example, if you push a car with your hand, but it has not been pushed, then the car is subjected to static friction.

The influencing factor is the external force that balances with it, just like how much force you use, how much friction there is, because it is stationary, and the force experienced horizontally balances each other and is equal in magnitude. However, it should be noted that there is a maximum value of static friction, and the maximum value of static friction is equal to the magnitude of sliding friction when the roughness of the contact surface and the amount of pressure applied to it remain unchanged. Rolling friction is the friction experienced by the wheels when they roll on the ground, and junior high school does not require in-depth study.

The friction force is opposite to the direction of movement, generally the traction force is greater than the friction force, so that it is an acceleration movement, and vice versa. In a straight motion at a constant velocity, traction = friction.

What the teacher said makes sense

I wish the landlord a good progress!

The rough surface is uneven, and the two such planes are together where one surface protrudes will insert the other surface where it is concave, forming a staggered trend, so that if you move the protruding place of one plane, it will get stuck in the protruding (or concave) place of the other surface, hindering its relative motion, which is friction.

If the surface is very uneven, then the more likely it is to get stuck in the protruding places when there is a relative tendency to move, and the more the friction coefficient is relative to the macroscopic, the greater the friction force. When there is a force acting on an object in the horizontal direction, the surface of the two objects may be separated a little, so that the places where they intersect have a certain degree of separation, so that the cross is not very deep, and relative motion may occur. If there is a force that presses them tightly together, then they will be stuck deep with each other, and it will be difficult for the relative movement of the side car, which corresponds to the greater the positive pressure on the macroscopic level, the greater the friction.

Broadly speaking, there is no direct correspondence.

But it can be summed up in two trends:

For dry friction conditions, the lower the surface roughness, the lower the relative coefficient of friction;

For wet friction, generally for friction with oil lubrication, the surface roughness is not lower than the better, generally speaking, the rz is lower than for the oil friction between the cast iron and the cast iron I use, in other cases for reference only) The following is not conducive to the formation of oil film measurement, and the friction coefficient is increased. It can be said that in an oily environment, the lower the better. There is an equilibrium value, and the specific friction pair needs to be tested and explored.

These are two concepts.

Relative roughness.

It refers specifically to the ratio of the rough protrusion height of the pipe wall (absolute roughness) to the inner diameter d of the pipe, that is, d, which is the number of unfactored times.

in laminar flow. , the flow system flows in parallel and no vortex is generated, so the friction coefficient of the pipe wall has nothing to do with the roughness. During turbulent flow, roughness has a significant effect on the coefficient of friction of the pipe wall. The greater the roughness, the greater the impact.

Coefficient of friction: refers to the ratio of the frictional force between two surfaces and the perpendicular force acting on one of their surfaces. It is related to the roughness of the surface, not the size of the contact area. According to the nature of the motion, it can be divided into dynamic friction coefficients.

and the coefficient of static friction. Sliding friction is produced when two objects come into contact with each other and slide relative to each other.

The amount of friction is related to the smoothness of the contact surface (the smoother the contact surface, the less friction the object is subjected to; The rougher the contact surface, the greater the friction experienced by the object).Friction is related to objects rubbing against each other, so the description of friction in physics is not generalized and not as precise as other forces. Without friction, shoelaces cannot be fastened, and screws and nails cannot hold objects in place.

The biggest distinction within friction is between static friction and other frictional forces. Some people believe that static friction should not actually be counted as friction. All other frictional forces are related to dissipation: it reduces the relative velocity of objects rubbing against each other and converts mechanical energy into heat.

The friction between solid surfaces is divided into sliding friction, rolling friction, static friction, rolling friction and rotational friction. In engineering, lubricants are used to reduce friction. If two surfaces rubbing against each other are separated by a layer of liquid, then liquid friction can occur between them, and mixed friction can also occur if the liquid is not completely isolated.

Air cushion rails work by using gas friction. Both the lubricating oil and air cushion rails work by using "friction with a liquid or gas (i.e. fluid) instead of a solid friction".

If lubricating oil, liquid, or gas flows along a solid surface, its velocity is reduced by friction. The structure of the solid surface has less influence on this frictional force, the most important being the cross-sectional area of the fluid. The reason for this is that there is friction not only at the interface between the fluid and the solid, but also between the different layers inside the fluid, and the flow velocity of the fluid is different depending on the distance from the solid surface.

There are two factors that affect the amount of friction: 1The magnitude of friction is related to the pressure between the contact surfaces, and when the roughness of the contact surface is constant, the greater the pressure, the greater the friction.

We have this common sense in life, when the bicycle is low on the tire, it is more laborious to ride. 2.The magnitude of friction is related to the roughness of the contact surface, and when the pressure is constant, the rougher the contact surface, the greater the friction.

What is a tug-of-war competition for? Many people will say: Of course, it is stronger than which team!

Actually, the question is not that simple. A force analysis of the two teams in the tug-of-war shows that as long as the tensile force is less than the maximum static friction with the ground, it will not be pulled. Therefore, increasing the friction with the ground becomes the key to victory or defeat.

First of all, wearing shoes with concave and convex soles can increase the coefficient of friction and increase the friction force; In addition, the heavier the weight of the players, the greater the pressure on the ground, and the greater the friction. When it comes to tug-of-war between adults and children, adults easily win, and the key is that adults weigh more than children. Also, in a tug-of-war, winning or losing depends a lot on people's skills.

For example, if you push the ground, you can put more pressure on the ground than you think on in a short period of time. Another example is when a person leans back, using the other party's pull to increase the pressure on the ground, and so on. The aim is to maximize the friction on the soles of the feet in order to win the game.

It is generally believed that the smoother the surface of an object, the less friction there is. But the smoothness is very small, and the friction increases.

That's right. Friction surface refers to the surface on which the relative moving parts interact with each other, and the difference between friction surface and non-friction surface can be measured by the surface friction value.

The surface roughness value is divided into 14 grades, and the smaller the surface roughness, the smoother the surface. The influence of surface roughness will change the service life and reliability of parts in mechanical operation, and reduce the mechanical efficiency. Since the 20s and 30s of the last century, many scientists have been working on the influencing factors of surface roughness and how to improve mechanical efficiency by changing the surface roughness of the grandson type.

Among them, the processing method and processing material have a great influence on it, and it is very important to choose the appropriate material and processing method. Surface roughness is a micro-geometric error that needs to be measured with a special tool.

<> experimental design: the same wooden block is pulled by the spring dynamometer to do uniform motion on the surface of the horizontal wooden board and the horizontal cotton cloth respectively, the wooden block is in a balanced state, the friction force of the wooden block is equal to the tensile force of the spring dynamometer, and the size of the spring dynamometer is read, you can know that the friction of the wooden block is large and the judgment is small, and the conclusion can be drawn by comparing the friction force; As shown in Fig

It can be seen from the spring dynamometer shown in the diagram that the friction of the wood block on the cotton cloth is greater than the friction on the wooden board, because the cotton cloth is thicker and bent than the wooden board, it can be seen that the rougher the contact surface, the greater the friction

So the answer is: as mentioned above

Friction is the "relative motion" of two objects that are in contact with each other and are about to occur, if there is or is about to occur between them, a frictional force that prevents this relative motion force will be created on the contact surface.

There are two factors that affect pressure friction, one is the amount of pressure, and the other is the roughness of the contact surface.

In experiments to study the relationship between the contact area and roughness and the friction force. Because of the shallow "degree", experiments usually collect 3 sets of data.

To study whether the contact area is related to friction, all that is required is a spring dynamometer and a cuboid with two different surface sizes; To study the relationship between roughness and friction, you need at least three surfaces with different roughnesses, such as glass, wood, towels, etc.

The friction force on the stationary object is the static friction force, and its magnitude should be found according to the force balance, and has nothing to do with the roughness of the contact surface, but the actual static friction is between zero and the maximum static friction, and the roughness of the contact surface can directly affect the maximum static friction.

The magnitude of sliding friction is directly related to the roughness of the contact surface, the rougher the contact surface, the greater the friction factor, and the greater the sliding friction under the same positive pressure.

Chapter 7 Motion and ForceSection 6 "What is the magnitude of friction related to the student's experiment".

Solution: From the velocity image of Figure B, it can be seen that in 0-t1, the acceleration is upward, and the friction force of the rope on Xiao Ming is greater than his gravity; In t1-t2, the frictional force is equal to the gravitational force when the velocity rises; In t2-t3, the acceleration is downward, and the friction force is less than the gravitational force.

According to the options, choose C

Only sliding friction is exactly what you say: it is only about pressure and roughness.

However, here is static friction (Xiao Ming climbs up along the rope, the rope cannot slip, otherwise it will not be able to climb high), static friction is a passive variable force, related to external factors, commonly determined by Newton's second law.