Tension is friction

1. Friction is determined by friction coefficient and pressure. No matter how hard you pull, as long as it is horizontal force, the car's pressure on the ground will not change, so no matter what kind of motion the car does, the friction will not change. It is 5N. When you pull with 5N force, the two forces will balance, and the car will move at a constant speed. When you pull with 6N force, the car will still move with 5N force, which is greater than the friction, so the car will accelerate

2. In case of static friction or uniform linear motion, the component force of pulling force in the direction of friction is equal to the friction force (in case of oblique pulling, such as being directly equal in a straight line)
in case of non-uniform linear motion, it is sliding friction force, f = UN, n is the pressure of vertical object, which can be calculated from the component force of pulling force and gravity

3. If the body moves at a constant speed, the pulling force and the friction force are equilibrium forces rather than interaction forces
the balance force acts on the same object
interaction force: if a has a pull force on B, then B has a pull force on A. these two pull forces are called interaction forces and must act on different objects

4. Thrust is equal to friction, because it does not move, indicating that there is no force, so friction is equal to thrust

5. It can't be generalized. You always remember, "force is what changes the motion of an object."
this analysis:
1. As you said before, the object moves in a uniform and straight line, that is, the speed and direction of the object do not change, so the combined external force on the object is 0. But now there is a pull force F = 5N, so there must be a friction force corresponding to it, equal in size and opposite in direction
2. Friction itself is related to the movement of an object, which is interpreted as "the force that hinders the movement or movement trend of an object". Its size can be divided into two categories: one is static friction, which is related to the movement trend of an object. As long as there is no motion, the external force is 0; The other is dynamic friction, which is only related to the weight of the object and the friction coefficient of the two contact surfaces
when the external force on the object is removed, if the object is still in motion, the friction force on the object is the same as that on the pulling force
3. When the speed of an object decreases to zero e to the obstruction of friction, the dynamic friction force on the object will be gone. The static friction force should be analyzed according to the actual situation. For example, if the contact surface is horizontal.

6. If the object is in equilibrium in the horizontal direction only under the action of friction and tension, then friction and tension are a pair of equilibrium forces
supplement: it is a pair of balanced forces, because these two forces act on the same object at the same time and belong to forces of different properties, and these two forces will cancel each other. A pair of action and reaction forces act on different objects respectively and are forces of the same nature. They will not cancel each other. For example, objects and the ground friction, objects friction the ground, the ground also friction objects, they are a pair of action and reaction.

7. In the experiment of "exploring which factors are related to the sliding friction", the sliding friction is related to the pressure and the roughness of the contact surface. In the experiment, the spring dynamometer should be used to pull the wood block at a constant horizontal speed, because from the knowledge of two force balance, the sliding friction force on the wood block is equal to the indication of the spring dynamometer. The friction force is measured indirectly. From the experimental data of Xiao Li, it can be seen that the speed of wood movement has no effect on the size of friction, so the conjecture that friction is related to the speed of object movement is wrong. If we want to verify that the size of the friction force is related to the size of the contact area between objects, we should control the size of the pressure and the roughness of the contact surface, and change the size of the contact surface to study. That is to say, put the wooden block flat on the long board, pull it horizontally and uniformly with the dynamometer, and read out the indication of the dynamometer. Then put the long board on the same side, pull it horizontally and uniformly with the dynamometer, and read out the indication of the dynamometer. Finally, compare the indication of the two dynamometers and draw a conclusion.

8. If acting on the same object, the object is in a state of static or uniform linear motion, then the tension and friction are a pair of [balance] forces!

9. It doesn't matter. The relationship can only be the problems themselves. Sometimes it seems to have a relationship. For example, if a pulling force acts on an object, there is friction between the object and the ground. When the pull is less than or equal to the maximum static friction, the friction is equal to the pull. When the pull is greater than the maximum static friction, the friction is equal to the maximum static friction.

10. The pulling force acting on the same object is not necessarily related to the friction force unless the acceleration of the object is known