A few questions about friction? 15

Friction is related to positive pressure and coefficient of friction, which is determined by surface roughness.

1。Regarding the problem of rope, each of the 10 turns of the rope is affected by friction, so the resultant force is naturally large, does this have anything to do with the area? . . There is still no, to explain that after multiple coils, in fact, the positive pressure for the rope changes, for example, a large plate, and a small plate, if they are placed on the same ground, and the quality of the two plates is the same, the coefficient of friction is also the same, then the friction force of dragging the two plates is also the same.

2。The problem of landing with one foot and landing with both feet, if the effect of the moment is not considered, then the friction force is exactly the same. It is easy to topple not because the friction is reduced, but because of its own balance problems.

Two. It is still necessary to look at the coefficient of friction and the positive pressure, in this case, it is necessary to look at the positive pressure on the friction surface, if you have to say that the area is related, that is, it affects the positive pressure falling on the friction surface.

Three. If you hold two boards on the ground, then it has an effect, because the positive pressure on the planks under your feet becomes less, otherwise there is none.

These problems really boil down to one thing. It is what the friction force is relative to. and how its size is calculated.

So. A 1 is not required. The magnitude of friction is related to gravity.

2 same. The premise is that it must be translational. It is not rotation (torque is calculated for rotation), and all four surfaces of 2 a b are subjected to friction. Specific to each force may be different in magnitude. But the resultant force of the four forces must be the same.

3. There is no change in the friction between the plank and the ground.

Seeing your problem, I feel that you still have some problems with your understanding of force. Just talk about force. It is necessary to mention who is the force against whom. Force is the interaction of an object with an object. Only understand this. In order to better carry out force analysis.

That's all it can say. I don't know if it will help you. Above.

If we imagine that there is no friction at all, then no object, whether a large rock or a small grain of sand, can no longer support each other. Everything has to be slid and rolled until it is laid out in a flat surface. Without friction, the earth would be like a fluid, a ball that has no height at all.

We can also add that without friction, nails and screws would slip out of the walls, our hands would not be able to hold anything, no building would have been built, and the whirlwind would never have subsided. We will constantly hear the echo of the sound that comes out as it reflects off the wall and is not weakened at all.

Every time there is ice on the ground, it makes it clear to us the importance of friction. When it freezes on the streets, we can't do anything about it, and we are in danger of slipping at any time.

Friction has nothing to do with the mask.

All of this you are talking about can be solved by a lever principle.

And you third don't understand what it means.

Friction has nothing to do with area.

1. The kinetic friction factor seems to be a number between 0 and 1.

2. It is not only these two kinds that determine the frictional force, according to the situation, the object placed on the horizontal ground depends on how much force you exert on it in the horizontal direction, when this force is less than the maximum static friction force of the trillion return, the static friction force of the object is equal to the force you exert, but its maximum static friction is related to the two points you said; The static friction of an object at rest against a vertical wall is always equal to its gravity, regardless of other factors.

3. The maximum static friction will be greater than the dynamic friction, the above-mentioned horizontally placed object is a good example, the roughness and pressure of the contact surface determine its maximum static friction, this force will be greater than the sliding friction that he slides up, but the sliding friction will not change, and the static friction is passively variable before reaching the maximum value.

4. The resistance of some movements is related to speed, such as some planes or trains, and the resistance he receives is proportional to the square of his speed.

5. Because it is a uniform motion, it must be balanced by the force, if you ignore the influence of resistance, then the buoyancy is equal to the weight of the person plus the weight of the umbrella. If there is resistance, the buoyancy will be a little less than this value.

Don't worry, I'll explain it to you Remember.

The first paragraph.

When placed vertically, pull A directly, AB is equivalent to a whole, so there is no friction between AB, but A has, and is equal to 20N, flat put, A has friction, B also has friction, if you want A to move, B also has to understand, so you have to overcome two friction forces, which is equivalent to them as a whole, so why is it also 20N, according to the vertical placement, AB is the same weight, 20N pulling force is constant, get A or B to put on the ground alone, the friction is 10N, so you need 20N when you put it flat

Second paragraph. When standing, B is on A, and the force acts on B, AB is constant, first of all, we can be sure that the friction force received by A is 30N, although B does not move relative to A, but it will also be subject to the friction of 30N, but it is static friction, and it can be determined that the friction between AB is greater than or equal to 30N, otherwise relative displacement will occur, when pushing A, I think of a whole, and I know that the friction force of A is 30N