The direction of sliding friction 20, the direction of sliding friction

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The book above does not move forward.

Answer: The reason why the force maintains the motion state of the object, the upper book was originally balanced by the force, but the lower book was pulled back, and the friction of the lower book has two, the palm of the hand and the upper book, both of which are resistance, and the upper friction is recorded as f1, and the direction is opposite to the direction of motion, that is, forward. And the upper book is also subject to friction and f2 is an interaction force, therefore, the direction of f2 is backward, which can be understood as a driving force, that is, the two books move backwards together.

You can look at the two books as a whole.

However, it is possible that the two books have relative motion, when the book is pumped hard, the acceleration of the book below A1 is very large, and the friction force produces the acceleration A2 on the upper book, and then there is a situation, the force you use to pump the book is very small, and you can't pull it at all, that is to say, the force of the book is "the friction of the palm, at this time the two books will not move, and there is no friction.

1. The direction of friction: opposite to the relative direction of motion between objects; Or always hinder the relative sliding between objects.

2. Judgment method: AB is in contact with each other, there is pressure between AB, and there is a friction coefficient between AB: A slides to the left relative to B (or has a relative sliding tendency), then the friction force of A by B is to the right.

Sliding friction is a method of determining the direction of sliding friction between two objects that are in direct contact with each other and have relative motion: the direction of sliding friction experienced by an object is opposite to the direction of its relative motion.

For example, there is sliding friction between a and b.

The direction of the sliding friction that A receives (given) is opposite to the direction of motion of A's relative (B).

The direction of motion of A relative to B: See the direction of motion of A (effect) on B.

The formula for calculating sliding friction is f = n, and the dynamic friction factor in the formula is called the sliding friction coefficient, which is only related to the roughness of the material and the contact surface, and has nothing to do with the contact area; n is positive pressure.

Sliding friction: A force that occurs between two objects that are in contact with each other and slide relative to each other, hindering the relative sliding between them.

The direction of friction is opposite to the direction of the relative motion of the object or the direction of the relative trend of motion, not to the direction of the motion of the object, and friction can be used as a force or as a drag.

Properties of sliding friction:

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

When the pressure of the object and the roughness of the contact surface are the same, the magnitude of the sliding friction is independent of the size of the contact surface area.

The magnitude and direction of friction are independent of the direction of motion and velocity of the object.

Formula: f= fn (fn: positive pressure, not necessarily equal to the gravitational force of the object to which the force is applied: kinetic friction factor, is a numerical value, unitless).

The direction of the sliding friction is always tangent to the contact surface and opposite to the relative motion of the object. The so-called relative is still based on the force object applying friction as the reference frame. 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. The so-called "direction of relative motion" refers to the direction of motion of the "stressed object" relative to the "applied object".

For example, when a box is pushed on a moving car, the sliding friction experienced by the box is in the opposite direction to the direction of the box's motion relative to the car.

The direction of the sliding friction must be the opposite or the same as the direction of the object's motion.

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

Example: If an object is lightly placed on the left end of a conveyor belt that moves horizontally to the right at a uniform speed, the object moves to the left relative to the conveyor belt, and the object is subjected to the sliding friction force of the conveyor belt to the right, which accelerates the object's motion, and the sliding friction force on the object moves in the same direction as the object's motion.

The object slides on a rough horizontal plane, and the sliding friction force on the object is in the opposite direction to the object's motion.

When the object decelerates, the effect of friction hinders the relative motion of the object, and the direction is backward in the opposite direction of the object's motion.

Sliding friction: The force that hinders the relative movement between two objects that are in direct contact and squeezed against each other is called sliding friction.

Size: f= n

Direction: Tangent to the contact surface and the opposite direction of the relative motion of the object.

Conclusion: When the object decelerates, the direction of friction is opposite to the direction of the object's motion, which is backward.