I can t figure out a high school physics concept and I hope adults will advise you

The frictional force exerted on an object is the sum of all the frictional forces exerted on that object.

May be produced by one or more other objects.

For example, in the real life of the car, the friction of the car comes from the air and the ground.

The frictional force of another object against an object indicates the force applied by the friction force and the person who receives the force.

For example: the friction of the ground against the car, the friction of the air against the car.

As for "for example, sometimes the topic is about the friction of the table against the object, and then it says that the object has a different friction on other objects".

The frictional force of the table against the object, indicating that the force of this friction force is applied to the table, the object subjected to the force; "Objects have different friction on other objects", it is the object that applies the force, and the force is applied to other objects, not the table, which of course is different from the friction of the table against the object.

For example, if there is a slippery plate on the table, and there is a roast duck on the plate, the table has friction on the plate, and the plate also has friction on the roast duck, the applicator and the receiver of these two forces are different, they are two different forces.

It should be noted that the Z force of X on Y is exerted by X and Y is subjected to force.

the frictional force experienced by an object and the frictional force of another object against an object".

The former is the force exerted, and the latter is the force exerted on other objects.

Objects have different frictional forces towards other objects"

Yes should be different for the friction factor between the two objects.

The friction is relative, the friction of the table against the object and the friction of the object against the table are not the same, the two objects are not the same, although the size is the same, the applicator is different.

Teach you, draw a unit circle, the radius length of the unit circle is the length of the amplitude, imagine that a line segment with a length of amplitude rotates along the origin, then its projection length on the x-axis: x=acos, a is the amplitude, is the angle between the line segment and the x-axis, that is, we say the phase, so you can use the projection of the x-axis to represent a simple harmonic motion;

For example, x1=4cos( t+ )t+ ) is the phase, where t is the angular velocity w, and the following is the initial phase;

This initial phase is the angle between the line segment and the X axis when t=0, that is to say, the initial state of x1 is on the negative half axis of x, and then with the change of t, the line segment begins to rotate counterclockwise;

In the same way, the initial phase of x2 is 2, that is, when t=0, its initial position is on the positive half axis of the y-axis, and then with the change of t, the line segment begins to rotate counterclockwise;

Drawing the diagram of the unit circle, we can see that the phase of x1 is ahead of x2 2, so the vibration of x1 is ahead;

If x1=4cos(- t+), then with the increase of t, the phase will become smaller, and the angle between the line segment and the x-axis will become smaller, so it can be seen that the line segment moves clockwise, so for the vibration equations of x1=4cos(- t+) and x2=5cos(- t+ 2), it is the phase of x2 leading x1 2;

In addition, because the angular frequency of x1 and x2 is , so no matter when t is t, they maintain the phase difference of 2, which is equivalent to two line segments with an angle of 2 at the same time at the angular frequency of rotation, the amplitude of the synthesis is under the root number (1 2 + 5 2), you can draw a vector diagram yourself, the primary phase of the synthesis is the angle between the synthesis vector and the x-axis, and the synthetic angular frequency remains unchanged, so the vibration synthesis of the two can obtain a stable expression.

If two simple harmonic vibrations with different angular frequencies are synthesized, a stable waveform cannot be formed, as will be discussed in universities.

The phase is , that is to say, the phase difference of the simple harmonic motion is 2, that is, x1 is 2 ahead of x2

The phase difference of the simple harmonic motion is 2, i.e., x1 lags behind x2 by 2

First, from Faraday's law of electromagnetic induction, we can get the electromotive force e= nbs t

Then from Ohm's law of a closed circuit, we can get the current i=e r=nbs tr

where b t is unchangeable, and we bring it up then.

i=(ns/r) (b/t)

With this formula, we analyze the topic.

a - double the number of turns. That is, n doubled. It seems that i can be doubled, but when n is doubled, the resistance r is doubled, but i is actually unchanged.

b Doubling the area of the coil will inevitably increase the length, resulting in an increase in resistance. Nor will the current double the desired effect.

Doubling the radius in item c increases the area by a factor of four, while the perimeter is only doubled. Divide the two, and the current can be doubled.

D, since the current magnetic field direction is 60 degrees between the coil, its vertical component should be cos60 = two-way root number three. More than one-half. In other words, no matter how you change the angle, there is no way to double the magnetic field.

Naturally, there is no way to double the current.

A is not true, the number of turns changes and the resistance also changes; b is also not right, the resistance has also changed; Item c is correct; Item D is feasible and essentially changes the magnetic flux [by changing the effective area].

The key to choosing a is the direction, e is the vector, what is the definition of the vector positive and negative on the coordinate axis? It is positive in the direction of the arrow, and negative in the opposite direction of the arrow.

The direction of e is the direction of the force on the positive charge in the electric field.

To the right of the charge on the right, the positive charge is stressed to the right, so it is positive;

Between the right charge and the origin, the positive charge is forced to the left, so it is negative;

And so on. In addition, the electric field at infinity is zero, and when the charge is close to the point, the electric field tends to infinity. So choose A.

aThe electric field strength is a vector quantity.

The closer to the field source, the denser the electric field lines, and the greater the value of e.

The electric field strength along the positive direction of x is positive, and vice versa.

b At the midpoint of the two charges, the electric field strength is very small, excluding d When the distance from the charge is 0, the electric field strength can be considered infinite. Therefore, choose B

ABCD, all wrong, but B is the closest, let the line of option B pass through point O.

Vectors and scalars are not comparable, but you can compare the magnitude of scalars to vectors, such as the magnitude of displacement versus distance. Vectors can only compare sizes, note: vectors have directions and sizes, so vectors and vectors are not comparable.

Since it is a comparative size, you don't have to consider the direction, and the plus and minus signs before the vector indicate the direction, so you don't have to think about it, and I will explain it below.

First of all, the vector is spatial and not all directions can be represented by the plus and minus signs alone, and the plus and minus signs before the vector only mean the opposite or the same as the positive direction you specify, which is only limited to one coordinate axis, that is, it is either positive or negative. So the plus and minus signs before the vector don't make much sense when calculating, and this again involves mathematical knowledge, and I don't know what level of your mathematical foundation has reached.

To give you a simple classification, the plus and minus signs before physical quantities have the following meanings:

1.Indicates the nature of things: such as positive work, negative work, positive and negative charges, etc.

2.Indicates that the vector direction on a uniform line is the same or opposite, as "e" indicates that the direction of the field strength is opposite to the specified positive direction.

3.Compare the magnitude of the scalar with zero as the boundary, such as gravitational potential energy, electric potential, electric potential energy, etc.

If you have any questions, you can send me a message.

When comparing sizes, no direction is considered, only absolute magnitudes are compared.

At a certain time or position, there is also a direction, such as: velocity 5 meters and seconds, the direction to the east vector and the scalar cannot be directly compared, but the product of the vector is a scalar, can be compared with the flat method I hope you are satisfied.

I can tell you unequivocally that there is no comparison between the two vectors, and the speed we compare is actually comparing their velocity, and comparing their values.

Since you said it's vector, of course you have to think about the direction.

Second, at a certain point in time, they still have a direction. Be sure to judge the velocity of the object according to the topic, the direction of acceleration, and many high school topics are made here. Especially multiple-choice questions.

Vectors are vectors, and scalars are scalars and cannot be compared. Not as good as velocity and rate, one is the ratio of displacement to time, while the other is the ratio of distance to time.

But vectors and vector scalars and scalars are comparable.

For example, a force of -8n and a force of 2n are -8 N

It can be understood mathematically, that is, the relationship between the function and the independent variable is a one-time function, that is, when the function image is a straight line, as long as the function image is not a straight line, it is a nonlinear relationship.

Systematic errors: Small errors that occur in a test because they cannot be ideal, also known as regular errors. It is that under certain measurement conditions, when the same measured size is repeatedly measured many times, the magnitude and sign of the error value (positive or negative value) remain unchanged; Or when the conditions change, the error that changes according to a certain law.

Acceleration = resultant mass.

The external force experienced by the object has an upward pull force and a downward gravitational force, so f together = f pull - mg = ma

So it is t-mg=ma

Because there is a weight of 5kg under the string, it also has to bear the gravity of this 5kg weight.

t-mg=ma is an evolution of f=ma.

Do you want to know what quantity f is? It is the resultant force.

In the question you posted, the resultant force f=t-mg

That's why t-mg=ma and not t=ma.

The first problem is actually the problem of hook 3 strands, 4 strings, 5 sin, cos is adjacent to the hypotenuse, cos is the adjacent edge than the hypotenuse, tan is the opposite edge than the adjacent edge, and cot is the adjacent edge to the opposite edge.

So sin37=3 5 sin53=4 5 cos37=4 5 cos53=3 5

The common angles in physics are 30, 45, 60, and the 37 53 that you asked, which is something to remember, and the rest of the angles will give us data, which are all available in these math books.

Newton's first law is relatively simple, it is a problem of inertia, the third law is action and reaction force, in fact, as long as you remember that you need to act on different objects, the second law is throughout high school physics, do a little more practice, and you can get familiar with it.

High school physics is one of the more difficult subjects, so it's okay to study it badly for the time being, do more and think more.

sin53 degrees = degrees.

sin37 degrees = degrees.

Sinx degree = cos(90-x) degree.

If you are from Hunan, it is recommended that you read Wang Houxiong's book, his physics is good, I personally think that physics is still more done, master the basic question types, and use it well, and there will be no problem with difficult problems. You can ask the teacher about the books, but no more than three, generally do two, and it's OK to do it from beginning to end.

sin37 degrees = 3 5, 53 degrees 4 5 ......What you say is very simple, Newton is not a problem, but how to tutor you? Keep in touch.

Common methods in physics: Method: Synthesis of vectors and orthogonal decomposition.

sin37 degrees is the hook three strands, four strings, five.

A: According to the kinetic energy theorem, ek = ep, ab height is the same, and the resistance is not counted, so the kinetic energy of ab point is the same, and the velocity is the same, which is correct.

B: A ball slides on the inclined plane, so g needs to be decomposed, the size is gsin (let the inclination angle be ), according to s=1 2gsin t can find the time t, B ball is in free fall, g does not need to be decomposed, according to h=1 2gt can find the time, the two equations are compared, gsin g, h s, it can be concluded that the time of ball A moving to a is greater than the time of ball B moving to b. Mistake.

c: Because the friction is not counted, the mechanical energy is conserved, and because the mass of the two balls is equal, both start to move from rest, so the mechanical energy of the two balls is equal. That's right.

D: According to W=PT, the work done by gravity at two points AB is equal, and the time is longer for ball A to move to point A, so the gravitational power of ball A is smaller than that of ball B. Mistake.

Answer: AC

I choose AC.

Gravitational potential energy is converted into mechanical energy. So c

Mechanical energy = 1 2 mv 2 m is the same so the velocity is the same, note that the velocity direction is different, the force in the velocity direction of A is mgsina is less than the vertical force of B, so the acceleration of A is less than B In the case of the same rate, A takes a long time. b wrong gravity does the same work, t a t b, so the gravitational power a b. D false.

a c correct.

Because the bevel is smooth, the mechanical energy is conserved. c correct.

a b On the same horizontal plane, the gravitational potential energy is the same. Of course, the kinetic energy is the same. So the rate is the same.

B is false, because it is clear that the time it takes for ball A to reach point A is greater than the time it takes for ball B to reach point B. Long time. Of course, the power can't be equal, so d is wrong.

The mechanical energy is conserved during the movement of the two balls, and both are the mechanical energy at the highest point, which is kinetic energy + potential energy = 0 + 0 = 0, c pair. Because the mechanical energy is equal and the potential energy at the dashed line is equal, the kinetic energy is also equal and the velocity is equal, a pair, the velocity component of a in the vertical direction is smaller than b, so the gravitational power of ball A at point A is less than the gravitational power of ball B at point B. I choose AC.