The physical forces of the super incomprehensible are related to the question of physical forces

1.If there is no friction on the horizontal plane, then what your teacher said is not right, it should be a uniform acceleration linear motion.

2.If there is friction in the horizontal plane, the friction can be calculated under known conditions, and then the friction force is equal to 2n, then a uniform linear motion should be done.

The direction of resistance is opposite to the direction of the force, and the direction of friction is always directed in the direction of the trend of movement.

If there is a drag force of 2n and the object is at rest, then it should be a three-force balance.

The learning ability section is not to think too much about it, and not to complicate simple problems. All you have to do is memorize the theorem. Actually, I don't know much about this.

I guess you're a middle school student like me.

Hee-hee......I think. A: (1) Imbalance. (Rest) (2) Yes (Friction) (3) No.

I'm dizzy!!

On a smooth horizontal plane, the pulling force on the left side of the object is 7n and the pulling force on the right side is 5n These two forces are in the same straight line and in opposite directions, the object does not move in a uniform linear line, and the object moves in a straight line with uniform acceleration. It's not balanced.

If there is static friction and the object is stationary, it must be balanced.

If it is a dynamic friction force, it depends on which direction it is moving,..

Anyway, two forces are collinear, equal, reversed, and acting on an object, which is balanced.

If it's not collinear, it's a force couple.

But if an object is on a horizontal plane, the pulling force on the left side of the object is 7n and the right side is 5n The two forces are in the same straight line and in opposite directions, but the magnitude is different.

If there are no other conditions, it should be a linear motion with uniform variable speed. The direction of acceleration is the side with the greater force.

If there is a resistance to the right and the magnitude is 2N, it is a three-force balance (7n left pull, 5n right pull, 2n resistance). The object is in equilibrium and either stands still or moves in a straight line at a uniform speed.

In your hypothesis, if the ground is smooth, it is impossible to do uniform linear motion, in other words, you are wrong, if you count the resistance, the simple understanding is that the resistance is the force that hinders the movement of the object, and it should be in the same straight line as the direction of the object's motion (even if the direction of the force is no longer the direction of motion, only the component of the direction of motion plays the role of resistance), and both uniform motion and rest are in equilibrium.

In equilibrium, the combined external force of the object must be zero.

Uniform linear motion is definitely in equilibrium, but the object in equilibrium is not only subject to two forces, but also three forces balanced, four balanced, etc., because at this time the object is subjected to the two forces of 7n and 5n, and these two forces cannot be balanced, so it is impossible for the object to move in a uniform linear motion, it should be accelerated to the right, if the object is moving in a uniform linear motion, then it must also be subjected to other forces, as you said, when it is resisted by 2n (the direction is the same as the direction of 5n, and in the same straight line), In this case, it is possible to do a uniform linear motion. It is also possible to be stationary, depending on the initial state of the object, if the initial state is stationary, then it is stationary, if the initial state is moving, then it is a uniform linear motion.

Two-force equilibrium refers to the situation when an object is in motion at rest or at a uniform speed.

The uniform linear motion mentioned in the textbook is for Newton's law, that is, it is carried out in the ideal state of "no friction, no resistance", so there is no need to consider resistance, as long as it satisfies that "the object is acted on by two forces, and these two forces are in the same straight line, in opposite directions", you should only use it when you consider the slope problem, but you already know trigonometric functions at that time.

It is indeed necessary to have friction, and it is the balance of the three forces.

1. When two forces are acting at angles to each other, their resultant force is equal to gravity. Two forces and gravity at angles to each other form a triangle, and the sum of the two forces must be greater than the third force, and the difference between the two forces is less than the third force, so it may be 20 N.

2. Since there is no picture, it may be like this:

Let the center of the smooth hemisphere be O, the small ball can be regarded as the particle A, and the upper part of the thin line is K.

The ball is subjected to three forces, you know.

Let the force along the thin line be f1, the force f2 perpendicular to the outward direction of the large sphere, and the gravitational force g.

then f1:f2=ka:oa

Only in this way can the resultant force of f1f2 be vertically upwards and balanced with gravity.

In this case, what do you think f1:g should be equal to?

That's right, it's ka:ko

Based on this proportional relationship, we know that g and ko are constant.

Whereas, the KA becomes shorter during the lifting process. So f2 becomes smaller.

In the same way, we can see that f1 does not change.

I don't know if it will help you.

Problem 1, because f2 and f1 are not on the same line, that is, the component of f2 may be equal in magnitude and opposite to f1 in the same line. So it could be 20 Ox.

Question 2, analyze the force, the supporting force, the gravitational force, the decomposition force, and then use the trigonometric function ratio to know.

The resultant force with f2 is in the direction upwards and the magnitude is 20n. In this case, it is possible to be stationary.

2.This depends on the position of the fixed pulley and the direction of the pulling force.

1 Solve it with the balance of Newtonian forces. Make a vertical upward force equal to 20n, and then use this force as the diagonal of the parallelogram, using the already two forces because from the beginning of the diagonal to the end point can be a result, this upper force is combined.

2 fn should be changed from large to small, because at the beginning the support force is the combination of the gravitational force and the pulling force of the ball, and after reaching the apex, the support force is only gravity.

Please refer to the above explanation.

Question 1: As long as the resultant force of the three forces is 0, it is OK, and it is OK to do it with a vector triangle. If the three sides of length 10, 20, and 20 can form a triangle, then the resultant force of these three forces can be 0.

Question 2: You should notice the slowness in the question, which means that the combined force of the ball is 0 at any time when the ball rises, first of all, the gravitational force on the ball is always downward, and the supporting force of the smooth hemisphere facing it is always along the radius away from the center of the circle. Connect the center of the circle and the center of the fixed pulley, connect the center of the fixed pulley and the center of the ball, and see the triangle for yourself, I haven't reached level 2 yet, so I can't get on the picture.

I remember doing one of these questions. That's how it works, I'll give you the picture when I'm second.

1. Is the speed related to the pull force (or)?

The speed of the change of velocity is related to the magnitude of the force, the greater the force, the faster the speed change, and if the object is not subjected to the force, the velocity does not change.

Two: Is the kinetic friction of an object constant? That is to say, if all other conditions are equal, if only the speed of the friction is changed, will the friction change? If not, then why?

The factors that affect the magnitude of sliding friction are the amount of pressure and the roughness of the contact surface, and have nothing to do with other factors or the speed of the object's movement.

3. Why are friction and tension the same? Friction and tension are not the same, only when the uniform linear motion or the object is at rest, that is, when the object is in equilibrium, the tension and friction are a pair of equilibrium forces, equal in magnitude, opposite in direction, in a straight line, but they are not the same and have no dependence.

Your question is very good, ask a few more whys, and if you keep doing so, you will definitely be able to learn physics well.

1.Power w=f

Traction) xv (speed) from this formula to see the speed vs. f

traction) is not directly related.

a(acceleration) = f

m acceleration is related to the size of traction. That is, as long as you can ensure that a traction force is applied to an object at all times, the resistance of the object can make the object reach infinite speed. (The magnitude of the force only determines the speed of the time required).

2.The kinetic friction force is not constant.

Kinetic friction = positive pressure between the object and the contact surface x friction coefficient (the friction coefficient depends on the nature of the two objects in contact, that is, the object slides on the stone and iron, and the friction coefficient is not the same).

3.It should be said that when the object is at rest or moving in a uniform linear line, the frictional force and the tensile force are equal (just the magnitude) (but the direction is opposite).

Because the net force of the object is 0 when the object is in the state of 2 above...

First. p=fv, your thrust remains the same, but if the speed increases a lot, the power still becomes a lot more.

Second. Regarding kinetic friction, as long as your positive pressure remains the same and the friction factor remains the same, then of course it will not change. It doesn't change no matter how fast you are, f = n, is the friction factor, and n is the positive pressure.

Third. You may be talking about a state of uniform motion or a state of rest, and these two states are states of equilibrium. In this way, the friction force can be the same as the pulling force, otherwise the pulling force must be greater than the friction force, so that the object will not remain in equilibrium.

What you say makes a lot of sense, there is no force and velocity increases a bird, history changes the motion of objects and the basis of maintaining the motion of objects.

I think it's important to understand physics in its own way, to figure out what each force does in the motion of an object.

The ball is subjected to three forces:

The gravity of the ball is m1g, and the direction is downward;

The support force n on the bevel is oblique to the ball, and the vertical bevel is diagonally upwards (top left);

The tensile force f of the lightweight string, diagonally upwards in the direction of the string (top right).

The angle between the string and the inclined plane = (90-30)-30 = 30°, and the ball is balanced by force in the direction parallel to the inclined plane

fcos30°=m1gsin30°

f=m1gtan30°=root:3 3=5,root:3,3

Balanced force in the direction of the vertical inclined plane:

m1gcos30°=fsin(90-30-30)+n

n = m1gcos30°-fsin30° = root number 3 2-5 root number 3 3 * 1 2 = 5 root number 3 3

The inclined block is subjected to 4 forces:

The slope itself is gravity mg, downward;

The ball is under positive pressure n, and the vertical bevel is obliquely downward (lower right).

Ground support force n2, upward;

The ground is the static friction f of the inclined block, to the left.

The inclined block is balanced by force in the horizontal direction:

f=nsin30°=5 root number 3 3 * 1 2 = 5 root number 3 6

The support force of the ground for a is n=g1+g2

There is no relative motion between the person and A, and they move to the right at a uniform speed together, first using the integral method:

A person and an object are pulled to the right by two strands of rope 2f

The dynamic friction of the ground towards a is f= n, to the left.

The person moves to the right at a uniform speed with a, thus:

2f=μn=μ（g1+g2)=

Rope tension: f=100n

The person is subjected to two forces, the static friction force f1 of a to the person is to the left, the rope tension force f is to the right, and the force is balanced in the horizontal direction, so f=f=100n

Calculation: The maximum static friction between a person and a is f1max = g1 = , so there is no relative slip between a person and a .

The static friction of the human foot against A and the static friction of A on the human foot are a pair of action and reaction forces, and the magnitude is equal and opposite to the direction, so the static friction of the human foot to A is 100N, and the direction is to the right.

In 1, the ground support force plus the pulling force of the person is equal to the gravitational force of the object, so the net force is 0

2 is the same as 1, the object is subjected to three forces, the "two forces" mentioned in the question can only refer to the gravity and the pulling force of people, the resultant force is 50n direction straight down, and this resultant force is balanced with the ground support force (from the balance should be 50n direction vertical upward), so the object is subjected to 0 external force and is in a state of rest.

In both cases, the object is subjected to 3 forces.

Gravity, lifting force and support force of the ground.

The first case says that the resultant force of the three forces is 0

The second case says that the resultant force of gravity and lifting force is 50n downwards, and what is not mentioned is the supporting force of the ground 50n upwards

Together, these three forces are still 0

Definitely not == on the same exercise book

It's easy! The first object is subjected to 3 forces, which are gravity 60n, vertical upward pull 3n, and ground support force 57n, gravity straight downward, and pull and support force upward, so the net force is zero.

And the second object is also subjected to 3 forces, gravity, pull and support Unfortunately, the second one does not count the resultant force, but the resultant force of gravity and tension, and the resultant force of these two forces is equal to the supporting force, and the direction is opposite.

Do you understand? I was so slow to draw that I had to type and explain.

Child, the second one is wrong, you have to remember: as long as the object is not zero in terms of net force, it will move, which high school has said.

Neither of these two is a matter of two-force balance, because the two bodies are subject to three forces: the first problem: the bottom has a support force of 57n on the object, and the direction is vertical upward, and the second question: the resultant force is also zero, and it cannot be lifted, and the table has a support force of 50n on the box, and the direction is vertically upward.

At that time, the second resultant force is also 0, and there is a support force of 50n.

How can the first resultant force be zero?

C should be chosen because the state of motion is determined by the external force applied to it and not by the change of a single force. In this problem, the resultant external force is always 0, i.e. the object is always balanced by the force, so the state of motion does not change. It is still a linear motion with a constant velocity at the original velocity.

You can also think of this problem in this way, from a broad symmetry perspective.

Since the two forces were the same before, and they are the same after the instantaneous change, then we can consider the two forces to be "fair and equal", and no force is more "special" than the other, so the effect of the two forces should be the same, and then they will cancel each other out and have no effect on the original state. If the velocity decreases or increases (stopping means decreasing to 0), then it means that one of the two forces is "more important" than the other, which violates the principle of "equality and fairness" and is impossible.

In fact, this kind of symmetry is widely used in the two basic disciplines of mathematics and physics. Hopefully, you can make more progress with the help of this kind of thinking.

I hope I understand that.