Seek the understanding of sliding friction in high school physics, and experience in high school phy

The formula of sliding friction depends on the conditions of the question, if the object is in relative motion, that is, the object is in motion, and the contact surface between the object and the horizontal plane must be rough, that is, only the surface of the object is rough, the horizontal plane is not rough, or only the horizontal plane is rough, and the surface of the object is not rough, this formula cannot be used. When an object is subjected to gravity, it exerts a pressure on the plane, which in turn gives the object a supporting force. On the inclined plane, the gravity force is vertically downward, and the supporting force is vertically inclined upward, and the gravity needs to be orthogonally decomposed, decomposed into the vertical inclined plane direction and along the inclined plane direction, at this time, the component force of the gravity in the vertical inclined plane direction is equal to the supporting force received by the object, and the sliding friction force of the object can be found by substituting the formula of this force.

This formula can also be used for the object having to move (or if the object is stationary and about to slide). If there is a force that is opposite to the relative motion, the friction does not increase, it is only related to the supporting force (the pressure experienced by the plane) and the coefficient of friction experienced by the object. If friction is resistance, in high school, it is considered to be the total resistance experienced in most cases.

The object will definitely experience other resistance, such as air resistance, but not in high school).

Hope these things can help you.

High school friction can also be a balancing equation.

The inclined plane component is built on the parallel inclined plane and the vertical inclined plane.

The frictional force only varies with the pressure and coefficient of friction, and is independent of other forces.

Not necessarily.

Friction is related to the balance of two forces and is static friction. The kinetic friction is naturally calculated according to the friction formula. Note that it is a positive pressure with the horizontal plane, which requires a force analysis.

Friction is only related to the amount of positive pressure on the upper, as long as the amount of positive pressure does not change, the amount of friction will not change. You have to understand the meaning and constraints of each quantity in the formula, and you will understand how the formula is derived. The derivation of the disclosure is much more important than the formula itself.

The gravitational force of the object is: g

g*tan37 = force down the inclined plane = (1).

g*tan53=friction=(2).

According to Niu Er's law, (1)-(2) is the external force of the object on the inclined plane, and the acceleration is divided by the external force by the mass.

Let the kinetic friction factor between the object and the inclined plane be that the mass of the object is m

1) When an object slides upwards along an inclined surface, it is subjected to the gravitational force mg, the support force n, and the sliding friction force f (the direction is parallel to the inclined downward direction).

The acceleration is set to .

A1 is obtained from bovine two, f is combined with mg*sin, 37 degrees, and f m*a1

and f * n *mg*cos37 degrees.

The acceleration is.

a1 g*(sin37 degrees *cos37 degrees), the direction of acceleration is downward along the inclined plane.

2) When an object slides downward along an inclined surface, it is subjected to gravity mg, support force n, and sliding friction force f (direction parallel to the inclined upward side).

The acceleration is set to .

A2 is obtained from bovine two, f mg*sin, 37 degrees, f m*a2

and f * n *mg*cos37 degrees.

The acceleration is.

a2 g*(sin37 degrees *cos37 degrees), the direction of acceleration is downward along the inclined plane.

Because the problem lacks a condition: the kinetic friction factor, if this factor is known, the acceleration value in both cases can be obtained.

Hello! In the case of sliding up, acceleration = sliding force mg*sin37 + sliding friction. In the case of sliding, it is necessary to see whether it is deceleration or acceleration, acceleration situation a=mg*sin37 - sliding friction.

In the case of deceleration, a = sliding friction - mg*sin37%$$

Static friction refers to the friction force that occurs when an object has a tendency to move when it is at rest, which is called static friction, and static friction is the force when it is in equilibrium. Therefore, the magnitude of the static friction force can be analyzed according to the equilibrium state and the static friction force can be calculated.

The magnitude of the sliding friction force is opposite to the relative direction of motion of the object, the sliding friction is a kind of dynamic friction force, and the magnitude of the mode tension force is only related to the roughness of the contact surface and the amount of pressure. There is no relationship between the velocity of the object and the size of the area of the contact surface.

It is proposed to use the above method to measure, when the blocks are pumped, the friction between them is the sliding friction.

Static friction and sliding friction are studied.

Don't think about the ground, just consider whether the two objects in contact with each other have sliding against each other, if it happens, it is sliding friction, and if it doesn't happen, then it is mostly static friction, and it is possible that there is no friction.

There is no relative sliding between objects that are in relative contact with the static friction, only a tendency to move relatively. Sliding friction is generated when there is relative sliding between objects in contact. There may be static friction between moving objects and sliding friction between stationary objects.

1. The causes are different, if two objects that are in contact with each other and squeeze each other, and are relatively stationary, if they only have a relative sliding tendency under the action of external forces, and no relative sliding occurs, the force that hinders the relative sliding between their contact surfaces 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 static friction force of the different direction of the force is always opposite to the direction of the relative motion 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 maximum static friction is greater than the sliding friction, and the rolling friction is much smaller than the maximum static friction and sliding friction.

The conditions under which static friction is generated.

1) Two objects are in contact with each other and squeezing each other; (2) The contact surface is rough; (3) There is a tendency to relative movement. All three conditions must be met, and none of them is indispensable. The effect of static friction is to hinder the relative motion of objects and keep them relatively stationary with each other.

3. The direction of static friction.

The direction of the static friction is always tangent to the contact surface and is opposite to the direction of the relative motion trend of the object. The relative motion trend can be understood as follows: relative motion refers to the change in the position of an object relative to another object, and the relative motion trend is that the position of the object is originally going to change, but due to the obstacle of static friction, the object is no longer moving, and the direction of its friction is opposite to the direction in which the object will move.

Fourth, the magnitude of static friction.

There is a maximum value of static friction, which is called maximum static friction, which can be expressed in terms of fmax, which is equal to the minimum external force required to make the object just about to move. When the external force gradually increases but the two objects remain relatively stationary, the static friction increases with the increase of the external force, but the increase of the static friction can only reach a certain maximum. When the magnitude of the external force is greater than this maximum, the two objects will move from relative rest to relative sliding.

This maximum value of static friction is called "maximum static friction". Assuming that the maximum static friction is fmax: then the static friction f is between 0 fmax, i.e., 0 f fmax.

The maximum static friction fmax is proportional to the positive pressure n of the contact surface, and the maximum static friction fmax increases with the increase of positive pressure n and decreases with the decrease of positive pressure. It can be calculated using the formula fmax = n. It can be concluded that the magnitude of the static friction force is not a fixed value, and the static friction force varies with the actual situation, and the magnitude is between zero and the maximum static friction force.

Its value is determined by the external force on the object at this time.

A must first be forced, and then remain relatively stationary with B to have static friction.

The reverse is the same for b.

There is also a rough contact surface of A and B.

To put it simply, for example, after an external force is applied, but the object does not move, it means that there is static friction.

Do A and B have relative motion or a relative movement trend?

Is it in equilibrium? If yes, no.

Once you have performed a force analysis on A and B respectively, the problem is solved.

Let's look at b first, b is subjected to a force f to the right, although there is a tendency to move, but it is still at rest, indicating that it is also subjected to a frictional force f to the left, and f = f

In addition, B is subjected to the downward gravitational force g, the upward ground support force n, and the downward pressure n of A on it, n=g+n

Looking at A, A is supported by gravity G and B, and the two are equal in size and in equilibrium. If A is again subjected to the friction of B, an external force must cancel out the friction to keep A at rest.

B has friction with the ground, because it is the balance of force, there must be a small F balanced with F, so that B does not understand, and A is not subject to external force, of course, there is no friction.

When the whole is not moving, there is no friction between A and B. B is balanced by a pulling force of 5N to the left, so B is subjected to the friction of C5N to the right. Analyze C again, with 10 to the right and 5 to the left, the ground needs to give him 5N to the left

When the acceleration is 1m s2, it should be an overall acceleration and accelerate to the right. Since A needs the power of Ma, that is, the frictional force that B gives to A, there is between B and A. Analyze B again, it is subject to the leftward 5N tensile force and the leftward friction force of A to B, and a rightward friction force is still needed, and the resultant force is to the right, providing its acceleration to the right, so the relationship between b and c is.

Looking at C again, it is given to the left by 10n to the right and B to the left, and it produces an acceleration to the right, so the friction force given to it by the ground should be left.

When the whole is not moving, f ground is c = 5n (left), f c is b = 5n (right), and f b is a = 0

When the acceleration is 1m s (a to the right for example), f to c = left), f c to b = left), f b to a = right).

When the whole is not moving, fc=5n, fb=0, fa=0;

When the acceleration is 1, fc = 5- (fb = (, fc =.)

Answer: 10n 25n

Analysis: 1When the wooden box is pushed with a horizontal thrust of 10n, the wooden box does not move, and the force in the horizontal direction of the wooden box is balanced, that is, thrust = static friction = 10n.

2.When the wooden box is pushed with a horizontal thrust of 25N, the wooden box still does not move, so the thrust is still = static friction = 25N.

3.When the wooden box is subjected to 20n horizontal thrust, the wooden box happens to move in a uniform linear line, then the force in the horizontal direction of the wooden box is balanced, that is, thrust = sliding friction = 20n.

Static friction and sliding friction are not related to gravity and are related to support forces.

So f=u(fn) fn=g=100n, so u=20 100=

When pushed with 10N, the static friction is 10N.

When just pushed with 25N, the maximum static friction is 25N.

The coefficient of sliding friction is.

Because static friction is actually independent of weight, while sliding friction is the coefficient of friction * positive pressure.

1. When pushing with 10N, the static friction is 10N (the static friction force on the block will increase with the increase of thrust, and the thrust at this time is the maximum static friction when the block just moves).

n just started moving, so the maximum static friction is 25n

3. F=Un, F=20N, (N=100N, so U=The maximum static friction is greater than the sliding friction.

The maximum static friction of the object is known to be 400*.

Therefore, if you pull it with a force of 300N, the object will slide, and the frictional force will be applied even if the sliding friction is the maximum static friction: 100N.

And with a force of 50N, because the pulling force is less than the maximum static friction force, the object does not move, and the frictional force is the static friction force, that is, the tensile force of 50N.

Let the maximum static friction be equal to the sliding friction. Then f=

Pulling with a force of 30N, the object is at rest at this time, and the static friction force f1 = 30N

When pulling an object with a tensile force of 50N, the object slides, and the object is subjected to a sliding friction force f2=100N

Since the maximum static friction is regarded as the sliding friction force.

f = with a force of 300n, the object slides, the friction force is sliding friction is equal to 100n, the force is 50n pull, the object does not move, the friction force is static friction equal to 50n, if it helps, thank you, please ask if you don't understand.