Why is sliding friction an effect force while friction is a property force?

The effect force is defined according to the effect of the force, and the qualitative force is defined according to the nature of the force itself, such as "elastic force", it is the qualitative force, its definition is defined from "deformation", "restitution" and "generating force", it is not only the process of elastic force generation, but also the nature of elastic force, it has no trace of effect at all, it can never be said that it is powerful because of "elasticity", and the effect force can be said in this way: because it is the force that makes the object move, it is called "power"; Because the effect of the force of objects is to attract objects to each other, it is called "attraction"; Because it has a pressure effect on the plane, this force is called "pressure". Another example is that "friction" is a qualitative force, because there is no trace of "friction" in its definition, but "sliding friction", "rolling friction", "static friction" are effect forces, because literally there are already force effects such as "sliding" and "static".

In addition, in addition to gravity, the concept of other property forces is relatively broad, and generally contains several common effect forces, and the effect force can be borne by a certain property force, but no effect force can be said to contain a certain property force. The second method is the one I don't want my students to use, which is that there are only six types of physical forces in high school: "gravitational force, elastic force, frictional force, molecular force, electric field force, and magnetic field force".

Sliding friction is the generation of relative displacement.

Friction does not necessarily have to be desired for displacement.

Static friction: When two objects in contact with each other have a tendency to slide relative to each other, but remain relatively stationary, they act on each other to hinder the resistance of relative sliding, which is called static sliding friction, referred to as static friction.

Sliding friction: When objects that are in contact with each other (and squeezing each other) have relative sliding between each other, the friction that arises between objects is called sliding friction (or "friction that occurs when an object slides on the surface of another object"). Note that sliding friction is not kinetic friction!

Rolling friction: When an object rolls without sliding or has a tendency to roll on the surface of another object, the obstruction effect on rolling due to the deformation of two objects under pressure in the contact part is called "rolling friction". Its essence is static friction.

The difference between static friction, sliding friction, and rolling friction is the reason for their occurrence, the direction and magnitude of the force, and the specific details are as follows

1. The causes are different: sliding friction is the friction generated when an object slides along the surface of another object. Static friction is the frictional force caused by an object having a tendency to move on the surface of another object (when in fact the object is still at rest).

Rolling friction is the friction that occurs when an object rolls on another object.

2. The direction of the force is different: the direction of the sliding friction force is opposite to the relative direction of the object; The direction of the static friction force is opposite to the direction of the object's relative motion trend; The rolling friction is in the opposite direction to the rolling direction.

3. The magnitude of the force is different: the maximum static friction is greater than the sliding friction, and the rolling friction is much smaller than the maximum static friction and sliding friction.

Ways to increase beneficial friction.

1. Increase the roughness of the contact surface;

2. Increase pressure;

3. Turn rolling friction into sliding friction.

Ways to reduce harmful friction.

1. Replace sliding friction with rolling friction;

2. Separate the contact surface [form a layer of air cushion or magnetic levitation on the contact surface of the object];

3. Reduce pressure;

4. Reduce the roughness of the contact surface of the object.

Examples of friction in life.

Sliding friction: In life, the conveyor belt sends the goods from the low to the high place, which is achieved by the friction of the conveyor belt on the goods obliquely.

Rolling friction: The friction of the train's driving wheels is the driving force that pushes the train forward. The static friction of the driven wheels is the rolling friction that hinders the progress of the train.

Static friction is static with a relative sliding tendency but no relative sliding occurring, and the focus is on the trend. Whereas, sliding friction is the relative slip that has taken place.

Since the resultant external force on the object at rest is 0, the static friction force and the horizontal force on the object are balanced to a certain extent, which is determined by the balance of two forces, but the static friction force has a limit, this limit is the maximum static friction force, and its value f(max) 0n, where 0 is the static friction factor, and n is the pressure of the object on the horizontal plane.

If the static friction exceeds the maximum static friction, the object will move, and the horizontal force can be reduced to make the object move at a uniform speed, and the friction f n at this time is the kinetic friction factor, which is different from 0, and f is slightly less than f(max). The sliding friction force is not determined by the balance of two forces, because the object can do accelerated motion after motion, and the resultant external force is not necessarily zero

Sliding friction occurs between two objects that are in contact with each other and have relative sliding and relative motion, because these two objects have relative motion, they will hinder each other's motion, so a force that hinders relative motion is generated on the contact surface, we call this force sliding friction.

Static friction occurs between two objects that are in contact with each other, but relatively stationary, when there is a tendency to move relative to each other, a force will be generated on the contact surface that hinders the relative motion of the object, we call this force static friction.

The problem to note here is that an object subjected to sliding friction is not necessarily in motion, and an object subjected to static friction is not necessarily stationary.

(1) Static friction: When there is a relative sliding tendency between objects that are in contact with each other (and squeezed by each other), the friction generated between objects is called static friction. (or "There is a tendency for objects to move relative to each other, but there is no friction in relative motion".)

For example, a block that is stationary on an inclined plane is subject to the static friction given by the inclined plane.

2) Sliding friction: When there is relative sliding between objects that are in contact with each other (and squeezing each other), the friction generated between the objects is called sliding friction. (or "the friction that arises when an object slides on the surface of another object.")

For example, a block moving on a horizontal plane is subject to the sliding friction given by the horizontal plane.

3) Rolling friction: The friction generated when a "wheel-shaped or spherical object" rolls on the surface of another object is called rolling friction. For example, if a car is moving at a constant speed on a level road, the friction on the wheels is called rolling friction.

The greater the pressure on the sliding friction when the roughness of the contact surface is the same, the greater the sliding friction. The rougher the contact surface, the greater the sliding friction when the pressure on the object is the same. The direction of the static sliding friction fs is opposite to the sliding trend, and the magnitude is determined by the equilibrium condition.

The magnitude of the static sliding friction is a variable value, i.e., 0 fs fmax

Because the object is at rest when subjected to static friction, the force is balanced, so the magnitude of static friction is only related to the magnitude of the external force. Whereas, the sliding friction changes when the positive pressure changes.

Because the magnitude of sliding friction is determined by the nature of the friction surface and the pressure of the contact surface. The maximum static friction is also determined by the nature of the friction surface and the pressure of the contact surface. But in general, the magnitude of static friction is determined by equilibrium conditions.

Because the essence of static friction is to rebel against the tendency of relative sliding between two objects that are in contact with each other. If there is no tendency to slide relative between two objects in relative contact, then the magnitude of the static friction force is equal to 0.

I'd like to give you a brief and comprehensive overview of your question, because I was just as confused as you when I was a student, and now I finally understand a little bit. If you don't think about this question at the level of Newtonian mechanics, you always feel that the answer is incomplete.

Newtonian mechanics is a gravitationally centered mechanic that is closely related to our daily senses. In our daily life, we often divide force into power and resistance, and sometimes we use elastic force. In physics, we often refer to force as force, because our latent resistance can also be our subconscious power, such as an object on a conveyor belt, when it is transported upward, the direction of the static friction force is along the conveyor belt.

Therefore, it is more accurate to call it an action force, also because there is often a reaction force in practice, which is very important in Newtonian mechanics, because Newtonian mechanics does not study the interaction force between particles deeply, and often uses internal force for the internal parts of an object that can be regarded as one. The elements of a force are divided into the magnitude and direction of the value, and as long as one element changes, then it is a different force.

I think the force should be understood in Newtonian mechanics, and the acceleration and velocity we are talking about are actually the result of the change of force, rather than the possibility of change in acceleration and velocity itself. In other words, in Newtonian mechanics, changes in physical phenomena are the result of the action of forces, so it is necessary to have a deep understanding of inertia and force.

Talking about the previous lot, talk about your problem specifically, when you talk about the sliding friction force, then you will think of the non-smooth plane, this plane is often elastic, then the elastic force and pressure are a pair of action and reaction forces in the opposite direction, the size is equal, which is the premise of analyzing the sliding friction force. The predecessors have concluded that the sliding friction force = n, is the coefficient of friction, which is related to the smoothness of the contact surface, n is the pressure, and the point of action is the surface of the object. The appearance of the simple phenomenon of sliding friction shows that the object is in motion, which may also be a constant motion or a variable speed motion, and it shows that there is elastic force and pressure in the direction perpendicular to the sliding surface, which are in opposite directions and equal in size, remember that the point of action of elastic force is the object.

When we pull the object on the non-smooth plane, but the object does not go, then there is a static friction force, I suggest not to overemphasize the movement trend (as I just said, we may be affected by daily life, always think that the friction force is a resistance, which causes confusion when analyzing the direction of the force), but from the direction of the force, the static friction force can be regarded as a force parallel to the friction surface and the opposite direction of the interaction force of equal magnitude, that is to say, in the state of inertia at rest, The magnitude of the static friction force changes with the magnitude of the reaction force, otherwise the object loses its equilibrium, and it will produce acceleration and lose its state of inertia.

Because when there is static friction, it means that the object is not moving relatively, and the equilibrium static friction force of the directly applied force is equal to the applied thrust.

Kinetic friction is the dynamic friction factor. According to this, the amount of friction is calculated.

Static friction is the frictional force when an object is at rest, its magnitude is limited, beyond a certain limit, the object will move and no longer remain at rest.

Kinetic friction is the frictional force generated when an object is moving, and this friction should be balanced with the active force in order to maintain a uniform motion.

Its friction, a kind of friction, is also friction how to slide the size of friction is proportional to the size of the contact area, and the static friction should be because after all, it is equivalent to the static friction at rest, so it must have no relevance.

The maximum static friction is approximately equal to the sliding friction = n. You are confusing the concepts of "static friction" with "maximum static friction".

Let me give you an example: if a book is placed on a flat table, the static friction is zero, and if I put another book on top of it, the positive pressure is doubled, and the static friction is still zero; When a book is pressed against the wall, the static friction is equal to gravity, and I press it with more force, and the static friction is still equal to gravity.

1. The causes are different.

If two objects that are in contact with each other and squeezed each other, and are relatively stationary, if they only have a relative sliding tendency under the action of external forces, but do not slide relatively, the force that prevents them from sliding relative is called "static friction". When static friction occurs two objects are at rest relative to each other.

Sliding friction is the force generated between two objects with relative sliding on the contact surface that prevents them from sliding relative to each other. Sliding friction requires relative motion.

2. The direction of the force is different.

The static friction force is always opposite to the direction of the relative movement trend, and is not necessarily tangent to the contact surface, which can be judged by the equilibrium method. It can be a drag force or a driving force, and a moving object can also be subjected to static friction.

The sliding friction is always tangent to the contact surface and opposite to the relative direction of motion of the object.

3. The magnitude of the force is different.

The maximum static friction is greater than the sliding friction and the rolling friction is much smaller than the maximum static and sliding friction.

1. Static friction is the obstruction of an object by another object when it has a relative motion tendency on the surface of another object.

2. Sliding friction is the force generated on the contact surface between two objects with relative sliding that hinders their relative sliding, generally speaking, the friction generated when an object slides on the surface of another object.

The difference between static friction and sliding friction is that static friction is the force experienced by a stationary object, which has a relative sliding tendency but does not occur relative sliding. Whereas, sliding friction is the relative slip that has taken place.

Friction: 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.

Static friction:

Static friction is when two objects in contact with each other are relatively stationary, but there is a tendency to relative motion, a force will be generated between the contact surfaces that hinders the relative motion, and this force is static friction.

Definition: When an object moves on the surface of another object in the tangential direction of the contact surface or has a tendency to move relatively, a force that prevents their relative motion or tendency to move relative to each other occurs between the contact surfaces of two objects, and this force is called friction.

If two objects are in contact with each other and squeezing each other, and the objects are relatively stationary, if they only have a clear and cautious relative sliding tendency under the action of external forces, and no relative sliding occurs, the force that prevents the relative sliding between their contact surfaces is called "static friction".