Is static friction a force

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2. Static friction sometimes does work. For example, when an object is put on the truck, it accelerates and the object doesn't slide. At last, the two move together. At this time, it's time for static friction to do work.
but now the problem is that there is no static friction after the sliding friction disappears, because the two speed together. If you think about it, it can only be friction in the horizontal direction, Without a second force to balance it, can the object move at a constant speed of V = 6m / S?

3. The size of static friction is equal to the size of the thrust used or the size of the pull used
dynamic friction = positive pressure * friction factor

4. F = UN
F is the maximum static friction force
n is the positive pressure
u is the maximum static friction coefficient
but generally U is difficult to get, so the maximum static friction force is usually calculated by the method of force balance. When a force retreats from an object, it is the maximum static friction force. The maximum static friction force is close to the sliding friction force, Sometimes it can be approximately considered as equal to.
2. F = UN
F is the sliding friction force
n is the positive pressure
u is the dynamic friction coefficient
this is used a lot

5. The static friction can't be calculated in general.
it is calculated by dynamometer.
for example, when you pull a truck with 10N force (the truck doesn't move), the static friction on the ground is 10N.
when you pull a truck with 100N force (the truck doesn't move), the static friction is 100N. This is the conclusion drawn by Niu San.
the maximum static friction can be approximately regarded as FN * u (dynamic friction coefficient multiplied by positive pressure) < br/ >As mentioned above,
when the object is not moving, the static friction is equal to the driving force (the driving force is the resultant force other than the static friction)

6.

There is no calculation formula for both. The magnitude of static friction is related to the trend of relative motion between objects. The larger the trend is, the greater the static friction is. The specific value can be obtained through the force analysis of objects. The maximum static friction is slightly greater than the sliding friction, which is generally considered equal to the sliding friction. Sliding friction formula: F= μ N

Static friction:

when two objects in contact with each other have the tendency of relative sliding, but still keep relatively static, they act on each other to block the relative sliding resistance, which is called static sliding friction, or static friction for short, and is generally expressed by F. It is defined as the obstruction effect of another object on the surface of another object when one object has a relative motion trend. The magnitude of static friction can vary between 0 and Fmax (0 〈 f ≤ Fmax, where Fmax is the maximum static friction and is related to positive pressure). Generally, it should be solved by equilibrium condition or Newton's law according to the motion state of the object

sliding friction:

sliding friction is the force generated on the contact surface between two objects with relative sliding, which hinders their relative sliding. Generally speaking, it is the friction generated when one object slides on the surface of another object. It is always tangent to the contact surface and opposite to the relative motion direction of the object. The so-called relativity is still based on the reference frame of the object exerting the friction force. The value is approximately equal to the maximum static friction. When the roughness of the contact surface is the same, the sliding friction f is proportional to the positive pressure: F= μ N μ Is the dynamic friction coefficient)

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7. may not. The maximum static friction is a little bit larger than the sliding friction, but it can't be obtained directly from the formula of sliding friction.

8. When we push an object but can't push it, the object remains static, and the friction it receives is static friction; At this time, the friction force on the object and our thrust force are a pair of balance forces. That is to say, the static friction force is as large as the force we use
do you have a direct formula for the force we exert? Certainly not. We all apply it at will. We just need to know that when the object is still, the friction force is static friction force, and it is equal to the thrust force we put on the object

when an object is moving, the friction force on the contact surface is related to the positive pressure and the dynamic friction coefficient. This is the formula of dynamic friction force F = n* μ ， It is only related to these two factors, and has nothing to do with the speed of movement.