Whether the coefficient of friction is artificially defined or is it present in nature

To be precise, artificially defined. The theory of coefficient of friction is only a macroscopic appearance. There are two theoretical explanations I can remember.

One refers to the force between molecules close to each other, and the magnitude of the molecular force and the distance between molecules are inversely quadratic ratio; The pressure changes the distance between moleculesAccording to the mechanics of materials, the force and the distance are linear; Considering the above two relationships, the relationship between pressure and friction does not conform to a linear relationship. Of course, the above is just a personal reflection, but the molecular force is a microscopic phenomenon, and the tensile pressure changes the length of the material as a macroscopic phenomenon, so my thinking also has limitations.

One is that any plane is microscopically uneven, and the interaction force is generated. This microscopic interaction force is a randomly distributed force. Ideally, the Gaussian distribution is conformed.

Probabilistic analysis can be done. However, the force between the concave and convex peaks should be expressed is also a question.

There are a lot of personal opinions above. Please see the reader to question. Communicate with each other.

The coefficient of friction is only related to the roughness of the surface of the object, and the force used for the same object placed on the surface of different objects will be different, which is directly proportional to the roughness of the surface of different objects. It can be seen that the coefficient of friction exists and exists naturally.

But the magnitude of the value is artificially defined, and there must be a standard object with a coefficient of friction of 1. Just like the definition of density, the density of pure water is defined as 1; But matter itself has a density, even though the word "density" is also taken by man...

Hehe. Between two objects in contact, there is friction between the surface because it is impossible to be absolutely smooth, which is natural.

In order to measure the roughness of the surface of an object in order to calculate the amount of friction, a coefficient of friction is artificially introduced. So the coefficient of friction is artificially defined.

Definition: When the contact surface of the two members that make up the moving pair is not a plane, an equivalent is introduced for the convenience of calculationCoefficient of frictionfv and equivalent friction angle.

Relative motion at a uniform velocity.

If the contact surface of the two objects is a groove surface and the load q is not perpendicular to one of the sides, then the total friction force is at this time.

The calculation of the driving force p) is carried out according to the formula p=fδq, and fδ is called the equivalent friction coefficient.

It is related to the type of the groove surface, the direction of the slag only high and the friction coefficient of the load q. In the groove surface, fδ f sin( 2), f is the plane friction coefficient, and is the groove angle. For two objects with relative rotation, when the contact surface is a groove surface, the equivalent friction coefficient should also be used to calculate the friction moment instead of the friction coefficient.

With the introduction of this concept, it is possible to turn the problem of complex contact surfaces into a plane friction problem, which can be calculated in a simple way.

If the coefficient of friction is greater than 1, then the calculated friction force is greater than the kinetic force, then it will go backwards.

This is the reality. Sliding friction.

It is equal to the kinetic friction factor.

The product of the pressure at the contact surface. In reality, most of the time this pressure is greater than the sliding friction.

In fact, there are some special cases where the coefficient of friction is greater than 1: when the contact plane and the contact surface of the object are smooth at the same time (not generally smooth, but very, very, very smooth), then the object and the contact surface will be "cold welded", that is, the friction coefficient is greater than 1, and it is difficult to push and pull the object from all directions.

Kinetic friction factor (or coefficient of kinetic friction.

It is the relative motion of objects that are in contact with each other.

The ratio between the force of friction and the positive pressure. When the object is in horizontal motion, positive pressure = gravity. The dynamic friction factor of objects of different materials is different, and the rougher the object, the greater the kinetic friction factor. Digging branches.

f=n* is the coefficient of friction, if =1, it can only mean that the positive pressure n and the friction force f are equal.

Categories: Education, Science, >> Science & Technology.

Problem description: Definition and calculation method.

Analysis: The coefficient of friction refers to the ratio of the frictional force between two surfaces and the vertical 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 coefficient and static friction coefficient.

If the two surfaces are stationary with each other, the contact between the two surfaces will form a strong binding force Static friction force, unless the binding force is broken can one surface move to the other surface, and the force before the movement of the force before the destruction of the force is called the static friction coefficient s, which is written as follows:

Equation Fig. 1) fs is the static friction force.

or f sn n n is the vertical force.

And this destructive force is also the maximum force to make the object activate, and we call this force the maximum static friction force. Therefore, we should rewrite the above equation as:

Equation Figure 2).

After the object is started, such as a car after a while, it will slowly slow down, and finally come to rest, which means that when the object is moving, its surface and another surface, such as the ground, still have friction, and the experiment finds that this force is smaller than the friction force at rest, we define this friction force and the force perpendicular to the ground is called the dynamic friction coefficient k, which is written as follows:

fk＝μkn

So, from the above we can know s k

The coefficient of friction refers to the physical quantity of the ratio of the frictional force between two surfaces to the normal pressure, usually expressed by letters. It is a measure of the strength of the friction of the surface of an object or substance against the surface of another object or substance. The greater the coefficient of friction, the greater the friction between the two objects; Conversely, if the coefficient of friction is smaller, the friction between the two objects will be less.

The coefficient of friction depends not only on the properties of the surface of the object but also on the pressure between the two objects.

By extension, the coefficient of friction is an important physical quantity, which is very useful in a variety of industries and daily life. The most obvious of these is the application in the manufacture of machinery, because the operation of machinery is inseparable from friction, so understanding and mastering the coefficient of friction can help in the design and manufacture of mechanical parts. In addition, the coefficient of friction is widely used in various fields, such as materials science, geology, automotive engineering, construction engineering, and aeronautical engineering.

Since it is mentioned in the Meaning of Dingfu that the coefficient of friction is related to the contact pressure of two objects, we can have this relationship. When two objects come into contact, the incomplete regularity of their surfaces makes the contact point just a few points, and the excavation is not the entire surface. The size and number of contact points depend on the range of pressure.

The smoother the surface of the object, the smaller the contact points, which results in a lower coefficient of friction. High pressures lead to more contact points, which increases the coefficient of friction. In addition, humidity and temperature also affect the coefficient of friction, which decreases as humidity and temperature increase.

In conclusion, the coefficient of friction is an important physical quantity that affects a variety of fields, from mechanical engineering to construction and aeronautical engineering. Understanding the coefficient of friction in relation to pressure, surface shape, humidity and temperature can effectively address friction-related issues, such as extending the service life of mechanical parts by reducing the coefficient of friction in machine building. <>

The coefficient of friction (friction factor) is the ratio of the frictional force between two surfaces and the perpendicular force acting on one of their surfaces. It is and the roughness of the surface.

related, but not related to 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. When the object is in horizontal motion, positive pressure = gravity. The kinetic friction factor of an object of different materials.

Differently, the rougher the object, the greater the kinetic friction factor. The static friction factor is the ratio of the maximum static friction force to the pressure of the contact surface, and the dynamic friction factor is the source wheel of the sliding friction force.

The static friction factor is usually slightly larger than the dynamic friction factor of the ratio to the pressure of the contact surface, which is also the reason why the spring dynamometer indicates a slight decrease at the moment of pulling the wooden block in the friction experiment. To determine the direction of sliding friction, it is necessary to grasp the direction of sliding friction and the relative motion of the object.

in the opposite direction". The specific method is to first select the object subject to friction as the object of study, and then take the object in direct contact with the object of study as the reference.

Find the direction of the velocity of the object of study with respect to the reference, then the direction of the sliding friction is opposite to the direction of the relative velocity.

The basis for judging the direction of static friction is that "the direction of static friction is always in opposition to the contact surface, and opposite to the direction of the relative motion trend of the object". Here's how:

Firstly, the object subject to static friction is selected as the research object, and then the object in contact with the research object is selected as the reference object, and then the velocity direction of the research object relative to the reference object is judged by assuming that the contact surface is smooth, that is, the direction of the relative motion trend. Then, the direction of the static friction is opposite to the direction of the relative trend of motion.

In general, we can consider the maximum static friction between objects to be approximately equal to the sliding friction.

It's the same thing, it's just a different statement in different versions of the book.

The friction coefficient can usually be determined by the method of friction angle, and the method is generally: one of the two objects to be measured is placed obliquely as an inclined plane, and the other is placed on the inclined body and slides down along it, and gradually reduces the inclination angle of the inclined plane.

mgsin 0 = mgcos 0, get: =tan 0. （1）

0 is the friction angle, and if 0 is measured, you can know the value between these two objects, which is easy to see from equation (1):

When 0 <45 °, < 1, when 0=45 °, =1, when 0>45 °, >1.

Since the tangent function in the quadrant is in the range of (0, ), it is not necessarily less than 1, and the exact amount depends on the properties of the material, the condition of the interface, etc.

It's possible. Because what we usually see is less than 1, we develop habitual thinking. But in fact there are such examples.

The first thing to know is that friction is divided into two main categories: dry friction and wet friction. The friction between solid surfaces is called dry friction (which is mostly discussed in secondary school). The friction factor of dry friction is generally less than 1, but there are also greater than 1, and the following is the static friction factor between several materials:

Timber vs. Timber:

Leather & Metal:

Aluminium and aluminum: The sliding friction factor is only slightly smaller than the static friction factor, so it can also be greater than 1. Since the nature of friction there are various theories: bump collision theory, adhesion theory, electromagnetic force theory.

The various causes of friction should be a combination of them, not a single cause. The study found that the friction between the two surfaces that are very rough will be very large, which may be the main reason for the collision"Ultra-clean"The friction between the two surfaces will be greatly increased, which may be due to the fact that the surface atoms of the two surfaces are quite close together, resulting in the electromagnetic force between the atoms. There has also been information that the dry friction factor between the two surfaces can reach as much as 50.

However, these are the contents studied in engineering mechanics, and the friction factors involved in secondary school are all less than 1.

Of course, when the surface of the object is rough enough, the force required to propel the object on the plane is greater than the gravity of the object, and the coefficient of friction is greater than 1; In other cases, if the surface of an object is too smooth, such as rubber and glass, then there is an adhesion between the two, which will also make the coefficient of friction very large. If you look at the table of common friction coefficients, you can also see that there are cases greater than 1.

No, because the maximum friction coefficient is only 0.9, the friction coefficient is less than 1.

The coefficient of friction cannot be greater than 1, this is common sense!

No, the grinding coefficient is greater than zero and less than one.

Impossible: the coefficient of friction is an operation symbol prescribed by physics, which stipulates that it has its own characteristics and cannot be greater than 1; At the same time, this characteristic has been proven by numerous experiments (it can be inferred from the formula of the coefficient of friction: the frictional force can never be greater than its corresponding positive pressure).

Possibly, but in secondary school physics, it is generally accepted that the coefficient of friction of most contact surfaces is less than 1.

For example, the coefficient of static friction between copper and copper is, and the coefficient of static friction between rubber and solid

If it's just a question in middle school, it's better to default to less than 1.