In my first year of high school, I studied the reference department, and there was a physics problem

The laws of physics are the same in different frames of inertia, but not necessarily in physical quantities. Take your example as an example: under different frames of reference, the work done by a force on an object can be different, because the displacement is different under the same force in different frames.

When we say that we can think of the problem in a different frame of reference, we are saying that the laws of physics are the same in different frames of inertia. The so-called laws of physics have to be an equation in simple terms. Again, in this example, in two different systems, the definition of work is w=f point times s, although the result is different, but it is calculated in this way in any system; Then the kinetic energy theorem w = the amount of change in kinetic energy, which is also a physical law, and it is also true in any reference frame.

Conversely, for example, under the action of a force, the velocity of an object of 1kg accelerates from rest to 1m s, according to the kinetic energy theorem, this force does work. If you change the reference frame of 1m s in the opposite direction, then the object is accelerated from 1m s to 2m s, and the force does work. From this example, we can also see that it is normal and desirable for different systems to calculate work and energy with different results.

Remember: you can change the reference frame to consider the problem because the physical laws do not change, that is, you can use the relationship that the two sides of the equal sign are equal with confidence, but the two sides of the equal sign can change after changing the system; Don't just think that there are any physical quantities that will remain the same after changing frames of reference (even quantities like mass will change ...... after relativity).)

Specific to your question, the ground system, that is, the first one is right; The solar reference system, that is, the second is right, after all, it has run so far with the earth, and it is appropriate to do great work. The first step in thinking about physics is to choose a frame of reference, depending on which one you choose.

First of all, this uniform linear motion is not an experiment done on the earth, and it is not realistic, because there is no real uniform linear motion on the earth, it is all curvilinear motion.

Secondly, you have introduced two frames of reference into this diagram, one is the earth and the other is the universe.

If we take the earth as a frame of reference, then the work done is m 2

If you take the universe as the reference frame, the workmanship is m(2v0+1) 2 understand?

If you think that the earth is moving, then the objects that are stationary relative to the earth also have kinetic energy, and the kinetic energy increased after doing work is the work done, or the same, not to mention that you should choose a reference frame that you think is forbidden when considering the movement of the earth, this absolute rest does not exist, it is meaningless, can you point out which point in the universe is absolutely stationary?

If you consider only one side, the m object is in motion relative to the earth, and similarly, the smooth horizontal plane is also in motion relative to the earth, so the following equation is that you only consider the m object relative to the earth, and the smooth horizontal plane is regarded as stationary.

There is also a frame of reference that is only relative, and this question should use the smooth horizontal plane as a reference, not the earth.

-2v0 is their relative motion.

Alas, brother, you haven't learned this section of the reference system, review it well, it's confused **It's here.

The earth is generally as stationary.

Summary. Kiss <>

I'm glad to answer for you, you can ask about the first year of high school physics. When the objects have a relative sliding tendency, the friction generated between the objects is called static friction, and the frictional force generated at this time is called static friction. There is a limit to the static friction experienced by an object, and this value is called static friction.

The direction of the static friction is always tangent to the contact surface and opposite to the direction of the object's relative tendency to motion. The magnitude of static friction is determined by the motion state of the object and the external force, and has nothing to do with the positive pressure. <>

Can <> ask about the first year of high school physics?

Kiss <>

I'm glad to answer for you, you can ask about the first year of high school physics. When the objects have a relative sliding tendency, the friction generated between the objects is called static friction, and the frictional force generated at this time is called static friction. There is a limit to the static friction experienced by an object, and this value is called static friction.

The direction of the static friction is always tangent to the contact surface and opposite to the direction of the object's relative tendency to motion. The magnitude of static friction is determined by the motion state of the object and the external force, and has nothing to do with the positive pressure. <>

<>14 (1) to determine that the height of the experiment is the same (2) the total mass of the hooked code is too large, reduce the hook code quality.

Kiss <>

Physics learning method in senior one: all knowledge should be recorded comprehensively in the notes, the key points should be recorded in class, and supplemented after class. Because there is too much knowledge that needs to be supplemented in high school physics, it is very undesirable to record notes in the textbook, one reason is that there is too much knowledge that needs to be recorded and the blank area of the textbook is too small, and the other reason is that if it is recorded in the textbook, it will cause the textbook to be messy, which will affect both the memory effect and the mood.

I can't easily let go of any mistakes in every practice and exam. Don't accumulate mistakes in ordinary times, there is too much knowledge of physics in high school, and the study tasks are heavy every day, accumulate a few today and accumulate a few tomorrow, and in the end it will be difficult to return! In addition, we must learn to analyze the causes of errors, learn to generalize, classify, and draw infiences.

3. One question with multiple solutions, multiple questions into one! <>

<>There's one more thing, I'm sorry for you<>

1) The elastic force on the unilateral mask strap: According to Hooke's law, the elastic force can be determined by the elastic coefficient k and the force f, that is, the elastic force f = kx, where x is the elongation of the force f. (2) The elongation of the mask strap on one side:

According to the magnitude of the force f and the elastic coefficient k of the mask band, the elongation x of the mask strap can be calculated, that is, x=f k. Since the force f of the two sections of AB and CD mask straps is f, and the elastic coefficient k is the same, the elongation x of the unilateral mask strap is also the same, that is, x=f k.

1. No one says that there is gravity on near-Earth satellites, but what we all talk about when we talk about physics is that gravity provides the centripetal force.

2. Gravity refers to the force that arises due to the attraction of the earth, which is equal in magnitude to the support force of the earth facing it. This sentence illustrates the generation of gravity, which is a force generated by the attraction of the earth, not that it is gravitational, so to speak, a force produced by gravitational action; The measure of gravity can be derived by measuring the pressure on the ground.

Because f'It's very small, so you can think of f=g, as you drew on the diagram, g is gravity, in fact g is smaller than f. Gravity is provided by a component of gravitational force.

(1) At the equator, gravity and gravity both point to the center of the earth, and the magnitude of gravity is equal to the difference between the magnitude of gravity and the magnitude of centripetal force.

Specifically, for geostationary satellites, it should be considered according to the perspective of total weightlessness. As follows: in the high-altitude geostationary satellite, it is only subject to gravity, so all gravitational force is used to provide centripetal force, and other objects in the satellite (such as astronauts) are also gravity to provide centripetal force, and there is no elastic force between the astronaut and other things next to it (in a state of complete weightlessness, as if gravity does not exist, in fact, the gravitational force at this time is "gravity").

2) In fact, both centripetal force and gravity belong to the gravitational component. In fact, gravity is, to put it bluntly, supportive. On the ground at the equator, when an object rotates with the earth, it is subject to gravitational force f and supporting force n (at this time, the magnitude of n is equal to the magnitude of gravity, strictly speaking, the object cannot be considered to be subjected to "gravitational force, gravity, support force"), which is obtained by the formula of centripetal force.

The centripetal force of gravitational force is the supporting force, so the supporting force of gravitational force is the centripetal force.

Equivalent to the gravitational force at this time gravitational force centripetal force, if you ignore the influence of the earth's rotation, there is gravity gravitational force).

Regardless of the rotation of the Earth, or the absence of contact with the ground, gravitational force can be considered equal to gravity. The name gravity was coined before Newton discovered gravity, and it was only later that people learned that gravity actually arose because of gravity. To put it simply, these are the two names of a force.

The satellite moves in a uniform circular motion around the earth, which can be said to be the centripetal force provided by gravitational force, or it can be said that the gravitational force it is subjected to provides the centripetal force there.

The magnitude of the dynamic friction is only related to the pressure and the kinetic friction factor: f (kinetic friction) n direction is always opposite to the direction of motion: the movement to the right on the horizontal plane can know the reason why the dynamic friction force is horizontal to the left

The support force is always equal in magnitude and in opposite directions: the net force is zero in the vertical direction.

To the right is the positive direction: the net force in the horizontal direction is -4-10 -14n, so the net force experienced by the object is the force of 14n to the left horizontally.

The reason for this is that it is not subject to friction to the right.

The resultant force is to find the resultant force in the horizontal direction and the resultant force in the vertical direction for vector knowledge.

The direction of the kinetic friction force is opposite to the direction of motion to the left with a magnitude of 4n and a resultant force of 14n to the left.

There is no friction to the right.

The object should have an initial velocity that is decelerating to the right.

The resultant force is a force of 6n to the left horizontally and a force of 4n to the right horizontally. f umg 4n, that is, the friction force to the horizontal to the right is 4n, and there is a pulling force of 10n to the horizontal left, then the net force is 6n, I hope to solve your confusion and adopt my answer....

The main points of this question are:

1. The direction of friction only depends on the direction of motion, and it has nothing to do with the direction of force, the direction of movement in the question is to the right, the direction of horizontal friction must be to the left, as for the force to the left, the relative object is a resistance, which will gradually slow down the movement of the object, but in this process the friction force has always been to the left.

2. Calculation of the resultant force: the left friction plus the left resistance 10N, a total of 14N;

As for the fact that friction is the opposite of motion, and the object is also subjected to a force to the left, why does the object move to the right?

The object is still moving to the right because it has the energy to move to the right, and it has been moving to the right until it is not zero, and the object will stop after a certain distance of resistance along with the object, and then move to the left, you can calculate how far the object needs to move before it can stop.

The direction of sliding friction is always opposite to the direction of relative motion, and the object moving to the right must be to the left by friction, the calculation formula.

f= mg=4n There is also a force to the left, so the resultant force is to the left, and the magnitude is 14N

1。The resultant force is 14n2. The object does not experience friction to the right because the object is moving to the right, the resultant force = left force + left friction f=f(1)+f(f)=10+4=14

The resultant force is 14n2. Resultant force = left force + left friction f = f(1) + f (f) = 10 + 4 = 14

If the object is moving to the right, then the frictional force experienced by the object must be to the left because the direction of the frictional force and the direction of motion are opposite. The force experienced by the object when moving to the right is: frictional force f=20*.

At this time, by the action of an external force to the left, the direction of motion is still to the right, and the direction of friction is also to the left, f=20*, so the net force is f+f=10+4=14n, and the direction is left.

When an object is moving, it is the dynamic friction force, which does not mean that the external force acting in one direction necessarily corresponds to the frictional force in the opposite direction, but the direction of the dynamic friction force is always opposite to the direction of motion. Unlike static friction, the direction of static friction is opposite to the resultant force of the external force.

The resultant force is 14n to the left; There is no friction to the right; The resultant force is calculated: f = mg 20 * the force of 10n to the left with the dynamic friction factor.

Friction is the opposite of motion The object also has a force to the left, why does the object move to the right...

In fact, the criteria for the selection of the reference system are how to analyze the problem and how to choose conveniently.

But what we see in real life is an intuition that has been formed over thousands of years. For example, the rain must have fallen vertically relative to the earth. If a person stands still, then what he sees must be a vertical fall, but now that a person is "moving", the result of that person "seeing" must be different from when he is standing still, and the reason for this difference is the speed of the person itself.

But the rain still falls like that, right?

I'll give you an example.

A boat travels against the current at a constant speed of 6 m s in a straight river channel, and the current speed is 3 m s, which is constant. At one point, the sailor accidentally dropped a lifebuoy into the water, so he reported to the captain that by the time the captain turned the bow of the boat and started chasing the lifebuoy down the current, it had been 5 minutes since the sailor had dropped the lifebuoy into the water, and asked how much time it would take the boat to catch up with the lifebuoy.

Under normal circumstances, we do this problem, because we are all accustomed to the geodetic reference system, we will involuntarily think of finding the ship's hydrostatic velocity, and then calculate that the ship's downstream speed is 12m s, and then continue to slowly solve the equation to find that it takes 5 minutes to catch up with the lifebuoy, the calculation is complicated, and it also involves the unit conversion ......

But what if you choose the flow of water as the frame of reference? Then the water is stationary, and then, it is equivalent to running 50 meters round trip, it takes 6 seconds to go, and coming back, if you don't slow down, it is also 6 seconds! After selecting the current as the reference frame, the velocity of the ship in the current, whether it is downstream or countercurrent, is the same "hydrostatic velocity".

This is the question of frame of reference, like this one, if you choose the current as the frame of reference at the beginning, you don't even need to calculate, just make sure that the speed of the ship and the speed of the current are constant, then the answer will be on paper.