What are some questions about Physics, Relative Motion, and Friction?

The understanding is a bit off, according to your understanding, it should be that there is friction in the process from the beginning of rest to the uniform motion. And in this topic, it has been said that the two move together to the right at a uniform speed, and there is no relative trend when the uniform movement has been done, let alone relative motion, so there is no friction. The process you understand is not the same as the process described in the title.

I don't know if I understand when I say that!

It's a deviation. However, if you make a mistake in your question or write it incorrectly, if the horizontal force acts on A, your question is too ridiculous, and the horizontal force should act on B. You have to keep this firmly in mind:

If there is a uniform linear motion in a certain direction, then the net force experienced by the object in that direction must be 0In the question, if an object A moves in a straight line at a uniform velocity, the force must be 0 in the horizontal direction, that is, there is no friction between AB.

If you are confused about how to start ab to do a uniform linear motion together, I suggest that you might as well assume that they are separated, a on a smooth horizontal plane, b on the horizontal plane of the problem, and ab with a rod connected between them. When AB moves in a straight line at a uniform velocity with the same velocity, do you consider the force on the rod?

I don't think the answer is correct, if there is no friction, can a move at a uniform speed under the action of a horizontal force? A has been subjected to a horizontal force to the right, and to maintain a constant velocity, it must have been subjected to the friction of B to the left; In this way, B is obviously subjected to the friction of A to the right, and in order to maintain a constant velocity, it is naturally subjected to the friction of the ground to the left.

Static friction is not friction.

Just think about this.

The answer is right. Because the title is about uniform motion.

If it is an accelerated motion, B will have a frictional force to the right on A...

f= n is used to calculate the sliding friction, where n is the positive pressure static friction can not be used by this formula, and the calculation of the static friction is calculated according to the balance of two forces.

Question 1: It belongs to the problem of static friction, and static friction and gravity are a pair of equilibrium forces. f increases, pressure increases. f=g remains the same.

Question 2: It belongs to dynamic friction.

First of all, the force in the vertical direction is g, f2, and f satisfies f=g+f2(equilibrium force) -1) The dynamic friction force formula is: f= n= f1 --2) Simultaneous (1) (2) has:

(f2+g/)f1

Question 1: Press the object against the vertical wall with force f and do not move It means that the wooden block is balanced by force. The pressure fn of the iron block against the wall is equal to the compressive force of the object against the wall.

In the vertical direction, the frictional force f is always equal to the gravitational force g and is constant. (No matter how much the pressure of the iron on the wall fn keeps getting bigger).

To use f= n, this is the formula for calculating the sliding friction force, > the static block in this problem cannot be used this formula, you should analyze the force balance.

Question 2: The wooden block happens to move downward at a uniform speed, indicating that the wooden block is still in force balance. In the vertical direction, downwards f2+g=f

f= n in the horizontal direction n=f1 so =(f2+g) f hope you study well!

The middle five pieces are at rest considering the force balance f=g=mg fn increases f does not change uniform motion force balance f=g+f2= n calculation =f2+g f1 principle: the rest of the block is subject to static friction The size of the static friction of the block is equal to the magnitude of gravity f= n, and the formula is not applicable.

Constant motion The sliding friction f= n is applicable, so it can be calculated in this way.

There is a relative moving friction, which can be used by this formula, i.e., sliding friction or rolling friction.

There is no relative movement of friction, no formula can be used, this friction is static friction.

When an object is stationary, it cannot be calculated using the friction formula, but the maximum static friction of an object in motion or in the street state can be calculated using this formula. Static friction is not affected by the action of external forces. So the first question, fn increases, f does not change.

The second question is a force analysis. In the vertical direction, the downward gravitational force and tensile force f2 and the upward frictional force are subjected, because they are in uniform downward motion, so the upward force is equal to the downward two forces; If it is known that the elastic force f1 is applied in the horizontal direction, then f = f1; And because f=g+f2, you can calculate it.

The key to this kind of problem is to see how much positive pressure n represents in f= n, there will be many forms of n in the specific topic, but the meaning is the same, the key to dealing with this friction problem is to distinguish what is positive pressure, and then you can apply the formula.

Big brother f=un is the calculation formula of sliding friction, the first question is that the object is "pressed against the vertical wall and does not move", so when analyzing friction, we should use force analysis.

Understand friction, sliding friction, static friction, maximum static friction. The basic concepts of high school physics are fundamental.

For the first question, because the slider is stationary, the friction force given to it by the wall is equal to the gravitational force on the slider. then the friction remains unchanged. You know this for sure.

We know that sliding friction is equal to the pressure multiplied by the kinetic friction factor. At this time, the slide remains stationary with the wall, so the formula of sliding friction does not apply, and can only be solved according to Newton's laws of motion.

For the second problem, since the slider is in relative motion to the wall, the formula of sliding friction is used. According to Newton's laws of motion, if the slider slides at a constant speed, the resultant force of f2 and gravity is balanced with the frictional force (numerically equal). So friction = f2 + mg

And the dynamic friction factor = friction divided by pressure, the pressure is f1, so it is as above the solution.

There is a relative sliding that can be used, otherwise it may not be possible.

a. Static friction has nothing to do with the positive pulsation pressure, A is wrong.

b. There must be elasticity with Hui Yinqing friction.

b right. c. The object is rubbed on the ground, and the ground is stationary, but the friction force is the friction force of the sliding friction.

d. If it is smooth, it will not be wrong.

So choose B

The friction of the second piece of paper is f, so the total friction is equal to 5*10 -3*f*(1+2+3+4......).Orange +999) = (100 * 499 + 500) * 5 * 10 -3 = 252n

f=f=252n

Kinetic friction is divided into sliding and rolling friction.

Generally, there is no rolling friction in high school physics.

So just ignore it.

Sliding friction as long as the contact surface in contact with the object is not smooth.

And there is a relative displacement.

It must exist.

The magnitude can be calculated directly using the formula for calculating sliding friction.

As for static friction.

Generally, it is necessary to combine the force analysis.

If the net force of the other forces is 0 in the direction parallel to the contact surface at the end, there is no static friction.

If it is not 0, it exists.

Because the final resultant force must be 0 in the parallel direction

Otherwise, it's not static friction.

In addition, if the topic talks about smooth contact surfaces.

No matter what kind of friction force there is, there is no such thing.

The relative direction of motion is the unequal velocity of two objects.

When the slow one is used as a frame of reference, the fast one moves forward relative to the slow one.

When the fast is used as a frame of reference, the slow moves backwards relative to the fast one.

The sliding friction experienced by the object is opposite to the relative direction of motion of the object's relative contact surface.