Why is object A placed on object B and thrown together upwards, and there is no force on each other

Because they have the same initial velocity and acceleration when they make a vertical upward throwing motion together, they always remain relatively stationary, so although they are in contact with each other, they do not squeeze each other, so they cannot produce elastic force, and there is no interaction force between them.

A b object can be regarded as a whole, because the initial velocity and direction of both are the same, and the acceleration is also the same, and naturally there is no force in motion.

a, b if they remain relatively stationary then there is no interacting force between them, if there is an interacting force, the effect of the force must be produced, and they cannot move together as a whole!

Let me be a physics major :

First of all: you also said that since they are thrown up together, "together" indicates that they are always in contact, so their speed is also equal, and they must have no force on each other in a relatively stationary state!

Again: I ask you, you can think of it this way, if there really is an interaction between them, would the two of them still be moving "together"? If there is an interacting force, it will definitely separate! Only when they are relatively stationary do they move together!!

Because the two objects are in a state of weightlessness.

You can assume that if there is a force, the acceleration of the object on it will be less.

And the acceleration of the object below will rain heavily so that the two objects will be separated.

There is force when accelerating up and decelerating, but not when there is a constant velocity.

To give you a classic physics common sense, objects with different weights fall at the same height and land for the same time.

Do you understand?

This question should be considered in parts and in its entirety! First consider the top C, C is at rest, suppose B has friction on C, then C is only subject to friction in one direction in the horizontal direction, then C should move, but C is stationary, so B has no friction on C!

Think of BC as a whole! A is subjected to a horizontal tensile force, and if B has no friction force against A, then A will move (same reason)! So B has friction against A, and according to the action and reaction force, then A also has friction against B!

From top to bottom, it's ABC

Let's look at a first, A is stationary, the force is balanced, the vertical direction of gravity and the supporting force are balanced, and the horizontal direction is not forced, so A will not be subject to the friction of B to A. If the A level is only subject to friction, it will be unbalanced.

From the analysis of A, it is found that there is no friction between A.

Analyzing B, it is still balanced by force, and there is a tensile force at the level, then there must be something else that balances it, which can only be the friction force of C to B.

So there is friction between the BCs.

Let object b be on a smooth and horizontal tabletop and suddenly give b a horizontal thrust f to the right, then:

A object: Subjected to gravity Ga, B to A's support force Na, B to A's right static friction force F. The gravitational and supporting forces are balanced, and the static friction forces change the motion state of A (from rest to right).

B object: the downward gravitational force GB, the downward pressure of A on it n, and the support force n of the desktop on B', horizontal thrust to the right f, static friction f from a to the left of b'。where gravity GB plus pressure n is balanced with the supporting force of the table, and the thrust f causes b to change the state of motion (from rest to motion).

The answer is yes, it's 0n.

Your sentence "So these two frictional forces are balanced, so the frictional force from A to B is also F, and the direction is opposite to the friction force given to B by the ground, that is, it is the same as the direction of the pulling force." "I think there's a problem. There is also a tensile force f, how can you judge the balance of two frictional forces?

It should be analyzed as follows: AB is in equilibrium with uniform speed movement. So a is either not a force in the horizontal direction or there are at least 2 forces that balance each other.

From the title, it seems that A is only subject to one frictional force at most, and it is impossible to equilibrate, so A is not subject to friction, that is, the friction between A and B is 0n. This is b by the friction of the ground as f.

Because A and B move together in a uniform linear motion, there is Newton's second law: any object always maintains a uniform linear motion or a state of rest when it is not subject to external force or the resultant force is 0. Therefore, this problem B is also doing a uniform linear motion, and the net force on A is 0, that is, the net force on A in the horizontal direction is 0, so there is no friction.

The reason your answer is wrong is that you can't directly tell whether there is a force between A and B.

The tensile force F and the frictional force of B are balanced by the pulling force F on object B, so there is no force between A and B.

If object A is placed on an object and object B is subjected to a tensile force f, what is the friction between A and B? The answer is 0, take b as the research object, b does uniform linear motion and its net force is 0, vertical direction b is subject to gravity and support force, they are a pair of balanced forces, and are not forced in the horizontal direction, if b is still subject to friction in the horizontal direction, it will do variable speed motion, not uniform linear motion.

A moves in a uniform linear motion, and the resultant external force is zero, then the frictional force between A and B is zero.

The conditions for the occurrence of friction are: Two objects are in contact with each other Relative motion or relative motion tendency occurs between two objects In Figure B, the weight and the wooden block are relatively stationary, and there is no friction

b will be subjected to the friction given to it by the ground. Because AB is in uniform linear motion at this time, both the vertical and horizontal directions are affected by the balancing force. Because it is a forceful pull B object, because the two forces are balanced, it cannot be a single reverse force, and there must be a friction force to balance it, and the B object is dynamic friction at this time, and the direction of friction is opposite to the direction of movement of the B object relative to the ground, so B is subject to friction at this time.

And A is also a uniform linear motion, because it does not experience other forces in the horizontal direction, (if there is a force, there is no force and it is balanced by two forces, which is not in line with the facts), so there is no friction between object A and object B.

Hope it helps, o(o

It does not move at a uniform speed and is not affected by frictional forces.

a. The object moves in a straight line at a uniform speed. Illustrates that the net force experienced by the object a is zero.

Analyze the force of an object:

Gravity and elasticity are balanced. There is no force acting in the horizontal direction.

Therefore, there is no tendency for AB objects to slide relative to each other.

Stress is applied by motion analysis.

If there is air resistance, since A moves in a straight line at a uniform speed, the force on A is balanced, and the frictional force of B on A is equal to the air resistance.

If there is no air resistance, then a is only subject to gravity and support, and the force is balanced. Since the friction force needs to be generated, there is elastic force between the two contact objects, and the two contact surfaces are rough and have a tendency to move relatively, and the common velocity of AB has no tendency to move relatively, so there is no friction.

Analysis of the force on B: B is subjected to gravity (the combination of AB) and the supporting force, the horizontal tension force f and the frictional force F (because of the uniform motion, the dynamic equilibrium friction force is equal to the tensile force), and the horizontal direction of A follows B to do a uniform motion, because of the dynamic equilibrium (the sum of all the forces on A is 0, and A is offset by gravity and support forces in the vertical direction and the horizontal direction is 0), so the horizontal is equivalent to the force and the air resistance is also considered a horizontal force.

This problem only needs to consider the situation after uniform velocity, if a is subject to friction, then there must be acceleration, which contradicts uniform acceleration... I would like to ask if you are teaching yourself Physics in your first year of high school?

High school physics does not need to consider air resistance, except for experimental questions and calculation problems with clear explanations.

Imagine that if B is a piece of ice, will A slip when you pull B, that is, it will not go with B.

Therefore, A must be forced to go, and A can only be subjected to the frictional force given to him by B to make A and B go together.

This kind of problem is not done with relative motion or relative rest, but force analysis. But it can be, if we look at a, a and b are relatively stationary, and a is relative to the earth in motion.

Dear, learn to analyze the force, and there will be more places to use it in the future.

I'm sorry, A, B are drawn in reverse!!

Because object b has acceleration, it is not an inertial coordinate system.

Therefore, in addition to the frictional force mg in the horizontal direction, a is also affected by a implicated inertial force am, when am= mg, a is immobile with respect to b; AM< mg A accelerates to the right with respect to B;

AM MG A accelerates to the left with respect to B.

It can be considered as follows: First, A must be acting on a force that can only be the frictional force given by B to A. Second, whether the relative motion is relative to rest depends on whether b accelerates the motion, if b accelerates the motion, ab has the same acceleration, and the initial velocity is the same, then it is relatively stationary; If b moves at a constant speed, ab is relatively stationary.

Thirdly, in the following question, "ab does uniform linear motion together" means that ab has no relative sliding. Suppose A has a slide on B, then A is only affected by friction on B, and there is acceleration when there is force, so A does an accelerated motion on B, and the title says that it is moving at a uniform speed, so A is not affected by force in the horizontal direction.

Hehe, you still haven't thought through the analysis of force.

Think about it, does a object have inertia? Assuming that there is no friction, then B is moving forward relative to A, then A will fall. (So it's a static friction).

But obviously, this phenomenon does not exist, A has pressure on B, the contact surface between the two is not smooth, and the two have a relative tendency to move, so there is friction.

It's a bit messy, welcome to ask!!