In physics, frictional forces include static friction and sliding friction. What are their concepts?

Definition of sliding friction: When an object slides relative to another object on the surface of another object, it is subjected to the force of another object that prevents it from sliding relative to each other, and this force is sliding friction.

Definition of friction: The tangential resistance that prevents the relative motion of two members when there is positive pressure between them.

Definition of static friction: that is, the maximum static friction, the friction force at the moment when the relative motion is about to begin.

When two objects in contact with each other move relative or have a tendency to move relatively, they will produce a force on the contact surface that hinders the relative motion or the tendency of relative motion, which is called frictional force;

Since these two objects directly follow only relative motion tendency, but no relative motion, it is called static friction;

When an object slides on the surface of another object, it is subjected to a force that prevents the other object from sliding, and this force is called sliding friction.

static friction; Refers to the occurrence of extrusion between objects. And at the same time has a relative tendency to move.

For example, a person walks on the ground.

sliding friction; Refers to objects that are squeezing each other and have relative motion.

For example, tires. The presence of friction means that the elastic force must be present, whereas the elastic force is not necessarily present.

The consideration here is that when the object changes from static friction to sliding friction, it has experienced the process of the object from rest to movement, and the tensile force provided here should not only overcome the maximum static friction, but also make the object move, that is, acceleration. But when the object is moving, there is no need for this acceleration.

Static friction and sliding friction are studied.

The maximum static friction is not less than the sliding friction - the maximum static friction is greater than or equal to the sliding friction, which is determined by the definition of "maximum static friction", because the static friction that does not satisfy the above relationship is not the maximum static friction. However, there is usually a situation where the maximum static friction is greater than the sliding friction, and it is irrelevant to explain this phenomenon that often occurs (but does not necessarily occur) regardless of the logical contradiction and definition mentioned above. This involves the theory of friction, which is so complex that it has not yet been conclusive.

Two models can be provided to explain qualitatively, but apparently they are not sufficient.

1) Compared with the two contact surfaces that slide against each other, the molecules (or atoms) on the contact surface at rest have sufficient time to be close to each other (in a certain range, the molecules are close to each other, which means that the attraction between molecules is larger), and the number of molecules with greater molecular force will be larger, so to overcome the attraction between these many molecules with larger molecular force and move, the external force should be greater - the maximum static friction force is greater than the sliding friction force.

2) Imagine that the surface in contact has many bumps and bumps, and the bumps between the two sides bite each other to become a ** of friction. When they are at rest with each other, they bite each other fully and tightly; When sliding against each other, the bumps have been ground (or pressed) flat on the front side – the bumps on the back side that can be bitten together have become shallower and smaller, so the sliding friction will be less. ,7,

Static friction exists between objects that remain relatively stationary, but there is a tendency to move, and the resulting static friction force acts, the magnitude of static friction can change, the object always remains stationary, and when the object is about to move, the magnitude of static friction is the maximum.

When the object moves in the horizontal plane, the object will be subjected to the obstructive force in the opposite direction of the horizontal face of the object's motion, that is, the sliding friction force, the magnitude of the sliding friction force is unchanged, and it is only related to the mass of the object, the acceleration of gravity, and the dynamic friction factor of the horizontal plane.

Static friction and sliding friction are studied.

Static friction, the resistance produced by objects pressing against each other and having a tendency to move relative to each other.

Sliding friction, the resistance created by objects squeezing against each other and moving relative to each other.

1. Correct, press an object by hand on the vertical car wall in the trolley driving forward 2. Wrong, in the direction of sliding friction, the object must be displaced, so it is impossible to be vertical, and it is possible to form an angle.

3. The pressure perpendicular to the contact surface of the object.

4. Correct, if the static friction is used, the friction has nothing to do with the positive pressure, and the dynamic friction is proportional to the positive pressure.

1. Yes. Static friction is an internal force between objects that is independent of the overall state of motion (velocity, direction).

2. Wrong. The existence of sliding friction must be the relative motion between objects, that is, the sliding friction force can only exist in the straight line where the relative direction of motion of the object is located.

3. A force that is in the same direction as the object or opposite to the direction of static friction. It can be understood as the force that causes a moving object to continue to accelerate or to bring a stationary object closer to breaking the static friction and starting to move.

4. Right. When a person pushes a stationary table, the positive pressure increases, but the table is not pushed, and the static friction increases with the increase of thrust. Once the force is large enough for the table to start moving, it changes from static friction to sliding friction, and the friction does not change when the thrust is increased.

a. Friction is to hinder the relative motion of an object or the relative movement trend, friction is not necessarily a resistance, or it may be a power so a mistake

b. The direction of sliding friction is always opposite to the relative direction of motion of the object, and may be the same as the direction of motion of the object, so B is wrong

c. The direction of static friction may not be high perpendicular to the direction of the object's motion, for example: the object at rest on the wall of the accelerating carriage, the direction of the static friction is perpendicular to the direction of motion, so c is correct

d. The elastic force is always perpendicular to the contact surface, and the friction force is along the contact surface, and the two are perpendicular to each other, so d is correct

So choose CD

Maximum static friction is a critical value that can be understood as a critical point for an object to move from rest to motion. If an object is to be moved from rest to motion, then the external force must be greater than the maximum static friction at the moment when the object is going to move.

The sliding friction force is the frictional force experienced by the object after sliding, and if the object is to move in a straight line at a uniform speed, the external force must be balanced with the sliding friction force.

A little understanding of the image is to make the object move, which is a process of changing the state of motion, the force should be larger, to reach the maximum static friction, in order to overcome the inertia of the object originally stationary, and after the object moves, the force can be relatively small, to achieve sliding friction.

The maximum static friction is the force required to push a stationary object.

Sliding friction is the magnitude of the force exerted on an object as it moves.

Stillness is as if an object is "glued" to the floor. Therefore, it takes a lot of force to destroy the glue. When you get moving, you need less force.

Kinetic friction is the ...... of sliding frictionThis is one thing.

There are two kinds of friction, one is static friction and the other is sliding friction.

Friction occurs when there is positive pressure between the objects, the contact surfaces are rough, and there is a relative or sliding tendency.

Sliding friction is when objects slide relative to each other, and they really move

Magnitude of sliding friction = pressure * coefficient of friction.

The coefficient of friction is a number between 0 and 1 and depends on the material properties of the contact surface.

Static friction is when there is a relative tendency between objects to slip, that is, they want to slide but do not slide.

Static friction cannot be calculated using the formula of sliding friction.

There are two objects with static friction that are relatively stationary (after all, "static" friction), so the force is balanced.

Other forces on the object can be analyzed first, and finally, the magnitude and direction of static friction (i.e., the magnitude of the resultant force of all forces except static friction in the opposite direction) can be obtained according to the equilibrium condition of the object (the resultant external force is 0).

Static friction and sliding friction must be clearly distinguished, static friction has no relative sliding, sliding friction has relative sliding.

Usually the maximum value of the frictional force is the magnitude of the sliding friction force, and when this value is reached, the object can be slid relatively

The words of the title ......

An object with a mass of 2 kg is placed on a level ground with a coefficient of friction.

Find: 1 When pulling an object with the horizontal tension of f=1 N, what kind of friction is experienced by the object and what is the magnitude.

2 What is the minimum external force to pull an object.

1 Solution: On a horizontal ground, the pressure of an object on the ground = gravity n = mg = 20 n

So the maximum static friction of an object is fmax= n=

Therefore, when pulling an object with a tensile force of 1n, the object is subjected to static friction.

The external force of the object in the vertical direction is already 0, and the external force of the object in the horizontal direction is also 0, so the frictional force f=f=1 n

The minimum external force pulling the object is the maximum static friction obtained earlier, i.e., the sliding friction fmax=2n

Sliding friction is a type of kinetic friction.

It is the kinetic friction that has relative motion.

There is a tendency to move relative to static friction.

Kinetic friction is divided into rolling friction and sliding friction.

Both cavity friction and sliding friction are equal to the force that makes it move (in equilibrium) and static friction you have to do according to the balance of two forces, depending on the situation.

Sliding friction is the force that hinders the relative motion of the contact surfaces due to their relative sliding. ok？

The dynamic friction is rolling friction.

Static friction is the phenomenon in which objects in contact with each other hinder their relative motion on the contact surface. The force that hinders the relative motion is called frictional force. Friction can be divided into static friction, sliding friction, and rolling friction.

static friction; Static friction is when you use a small force to push an object that is not moving, although the object is not moving, it has friction with the ground, and the object must overcome the maximum static friction before it can slide. Chopsticks can hold vegetables, and people can walk on the ground, relying on static friction.

Sliding friction. Sliding friction is the frictional force that occurs when an object slides along the surface of another object. The sliding friction experienced by an object is in the opposite direction to its motion, so friction occurs.

If there were no sliding friction in the world, people would push very heavy things faster than they could on ice! Rolling friction.

Rolling friction is the friction that occurs when an object rolls on another object. It is much smaller than the maximum static and sliding friction, and in general, the rolling friction is only 1 40 to 1 60 of the sliding friction resistance. So rolling an object on the ground is much less labor-intensive than pushing an object to slide.

Classic question: Among the following phenomena, the sliding friction is: a when sharpening the pencil with a pencil turner, the friction between the pencil and the inner wall of the rotary hole b the friction between the belt and the pulley when the belt is slipping when the belt is turned c the friction between the wheel and the ground when the bicycle brakes d d pushing the bicycle forward, the friction between the wheel and the ground.

Analysis: The friction caused by the relative motion of the contact surface is the sliding friction According to this principle, it is easy to get the answer a, b, c are all sliding friction, only d is the rolling friction Analysis: a, although it is a rotation process, but the relative motion between the contact surfaces is generated, and there are pen shavings.

b.Belt slippage, that is, the belt moves backward relative to the wheel, and the two produce relative motion, sliding friction cObviously, sliding friction is difficult to understand.

It turns out that when learning mechanical motion, there is a concept of reference object, when we study motion, we take an object as the standard, the tendency of relative motion refers to the possibility of moving in a certain direction, why it is called a trend, because it itself has no relative motion, but there is a trend, mainly because static friction prevents this trend, if there is no friction, what kind of motion will it be.

When an object is placed on an inclined plane, it has a tendency to move downward, that is, if there is no friction, it will go down the inclined plane, so the direction of the frictional force is parallel to the inclined plane upwards.

When a person is running, the sole (the latter one) is subjected to a forward friction force, because if there is no friction force, obviously, the shoe slides backwards relative to the ground, and it is not clear to ask questions if you are not clear.

Relative motion is a change in position relative to the objects in contact, such as when the object mounted on the car moves at a uniform speed with the car, although the object is moving relative to the ground, there is no change in the position of the car in contact, and the object is not subject to friction.

When a person walks, the foot has a tendency to move backwards relative to the ground, so the direction of friction on the foot is backwards.

For example, if you push an object hard, but it does not push it, then it is said that the object has a tendency to move relative to the ground, in other words, as long as the object is stressed but does not move due to friction, then the object has this tendency to move relatively.

When a person is running, the person's foot is pushed backwards, and there is a tendency to move backwards relatively on the ground, so the ground gives the foot a forward friction force.

Relative movement tendency, e.g. if you push a car but don't push it, the car has a tendency to move relative to each other (whether it wants to move or not).

When a person is running, the friction between the sole of the shoe and the ground is in the same direction, the person pushes the ground backward with his foot, the direction of movement of the foot is backward, and the friction force gives the foot a forward reaction force, and the person will run forward.

When an object remains stationary on an inclined plane, gravity causes it to slide, but friction makes it rest, which hinders the relative motion tendency.

When running, the friction is favorable due to the backward kicking and the friction force is forward.