How to determine the magnitude of sliding friction and static friction

1) Sliding friction: f= m fn

Note: Fn is the elastic force between the contact surfaces, which can be greater than g; It can also be equal to g; It can also be less than g

m is the sliding friction factor, which is only related to the material and roughness of the contact surface, and has nothing to do with the size of the contact area, the relative motion of the contact surface and the positive pressure n.

2) Static friction: its magnitude is related to other forces, solved by the equilibrium condition of the object or Newton's second law, and is not proportional to the positive pressure.

Size range: o 0 5 F static 0 5 fm (fm is the maximum static friction, related to the positive pressure).

Description: a. The friction force can be the same as the direction of motion or the opposite direction of motion.

b. Friction can do positive work, negative work, or no work.

c. The direction of friction is opposite to the direction of relative motion between objects or the direction of relative motion tendency.

d. Stationary objects can be affected by sliding friction, and moving objects can be affected by static friction.

1 Friction.

1) Definition: Two objects in contact with each other when they are about to occur or have been in relative motion. This creates an obstruction phase on the contact surface.

The force on motion is called friction.

2) The following three conditions must be met for friction between objects to occur:

First, objects are in contact with each other and squeezed.

Second, the contact surface is not smooth.

Thirdly, there is a tendency or relative motion between objects.

3) Be clear when understanding the concept of friction.

First. Friction is only possible when two objects come into contact with each other. Friction occurs when there is a tendency to relative motion or a relative motion has already occurred.

Second. Friction occurs in pairs, and the two objects A and B are in contact and have a tendency to relative motion or have occurred relative motion, then A is in production for B.

There is friction, and at the same time, B also has a frictional effect on A.

Third. There are two types of friction: static friction and dynamic friction. When two objects come into contact with each other, there is a tendency to move relative to each other, but there is no relative motion, and the frictional force at this time is called.

Static friction. If there is a relative motion between objects that are in contact with each other, the frictional force is called kinetic friction.

Fourth. The relative motion of objects when they come into contact. It could be sliding, or it could be rolling, so the friction could be sliding friction or it could be rolling.

Kinetic friction. Fifth. There is a tendency of relative motion between objects to mean that the objects are in a state of being moving but not moving, and the objects are still relatively stationary at this time, so they can't.

It is believed that objects at rest are not subject to friction; Conversely, moving objects are not necessarily subject to friction. For example, objects A and B are stacked on top of each other.

Moving in a uniform straight line along the horizontal plane at the same velocity, although both objects are moving, due to the magnitude and direction of the velocity of the objects A and B.

Similarly, there is no relative motion between them, so there is no friction between the two objects.

Sliding friction refers to the force generated by the friction between the object and the contact surface when it is in relative motion, and there is usually a dynamic friction factor. Static friction is when there is a tendency for objects to move relative to each other, but no relative motion occurs, such as when you pull a table but don't pull it.

Static friction and sliding friction are studied.

The maximum value of static friction is greater than that of sliding friction, while the magnitude of static friction and sliding friction cannot be compared. 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, which is generally represented by f.

When two objects slide relative to each other (or have a tendency to slide relative to each other), a force that prevents the object from sliding will arise between the contacts, and this force is called sliding friction, or friction for short. The frictional force acts on the contact surface of the object in the opposite direction to the direction of the slide (or the direction relative to the sliding trend). According to whether there is relative motion between the contact surfaces, sliding friction can be divided into two categories: static sliding friction and dynamic sliding friction.

1。Friction refers to the force that hinders the relative sliding of two objects that interact with each other when they are in relative motion or have a tendency to move relative to each other, and it is always the force that hinders the relative motion of the object.

2。The statement that "static friction can be a drag, it can be a driving force" is incorrect, and don't be superstitious about some books or authoritative explanations. For example, the belt conveys objects and extracts bricks with brick cards, the power is the role of the belt and the hand, and friction only plays an intermediary role, it is a kind of power caused by the action of pressure, and the value is not necessarily equal to the power.

Moreover, the direction of the static friction force is always opposite to the direction of the active force, and it is always the resistance that hinders the relative sliding of the object, rather than the driving force that prompts the relative motion of the object. In other words, it is always a drag to motivation and can never be called a driving force.

3。For rolling force systems, static friction is neither resistance nor power. It is an auxiliary force that stabilizes the transient center.

Some people use the direction of static friction to determine whether it is rolling resistance or power, and it is even more wrong. The direction of static friction is related to whether the rolling elements are subject to rotational or translational action, so it is not a discriminant condition of resistance and dynamics. Attention is drawn.

Static friction is also called maximum friction and friction between relative motion.

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

Imagine pressing the blackboard eraser with your hands, at this time it is static friction, slowly reduce the pressure, and at a certain moment, it is about to start relative motion (blackboard eraser) to fall, at this time the static friction is the largest, and then from static friction to sliding friction.

At this point, sliding friction is related to pressure!! And you have very little pressure, and the friction generated must not be as great as gravity, and the blackboard eraser will fall !!

Is it okay to explain it that way? If you can, remember, ahh!!hhh

In the case of a stationary opening bridge, the object is stationary when the friction is less than the maximum static friction. The frictional force at this time is determined by the external force and balances with the external force. If the flame decaying fruit object is in motion, for example, if it is moving in a uniform linear motion, the friction force and the dynamic force are equal to the kinetic force, which is slightly smaller than the maximum friction force at rest in the same scenario.

When the friction is less than the maximum static friction, the body will not slide.