Some issues of the National Applied Physics Knowledge Competition

First, explain the cause of the formation of the lower pressure.

Pressure, which is the pressure of the atmosphere on an object per unit area, is essentially the magnitude of the force generated by the gas molecules striking the wall of the device per unit area. If an object is placed on a tabletop, we say that the resultant force on it is zero, in addition to the gravitation force and the supporting force given by the tabletop, the atmosphere will also give it pressure, but the density of gas molecules around the whole object is constant, that is, the resultant force of the atmosphere on the object is zero.

Let's talk about the second problem, in the calculation process, any undivisible result must be fractional, this is done to reduce the error, for example: a problem has three steps, the first part of the calculation result is 1 3, the second part of the result is 5, the third part is 5 divided by 1 3, then the result is 15If the first step is to convert 1 3 to a decimal, that is, then the result must be greater than 15, because it is an approximate number, it is equal to 33 100, not equal to 1 3, so there is an error in the calculation result.

In calculations where errors can be avoided, if there is an error, then the result of the problem is wrong.

That's all, I hope it helps!

pressure, if there is atmospheric pressure, if it is a communicator, the atmospheric pressure on both sides can be offset; One side is sealed, and the other side is counted. Hey, I don't know this question, have you really read the two competition books? Didn't you get it in high school, did you? Isn't it allowed to bring a calculator to the contest?

You are already a master, the question you ask can be understood, about atmospheric pressure, often a practical problem to consider, the key is to see what the question of the question requires; Intermediate results can be used as fractions for the convenience of calculation, but the final results cannot be expressed by fractions except for the problems of ratio or multiples, because the physical problems are closely related to reality, and it is not intuitive to use fractions. The final result is often about 1 difference from the actual result, and no points are generally deducted.

Results can be expressed in terms of scores, and there is a big difference between a secondary school exam and a physics competition. Don't be nervous, relax, just think about everything before the exam.

In 2017. Since the founding of the People's Republic of China, the National Middle School Applied Physics Knowledge Contest Committee has organized the National Middle School Applied Physics Knowledge Contest in order to stimulate students' interest in learning science, expand students' horizons, promote the connection between middle school physics teaching and technology, society and daily life, better implement the three-dimensional goals of basic physics education, and effectively improve students' scientific and cultural literacy.

Significance. The competition highlights the application of physics knowledge in terms of content, focuses on the ability of students to apply physics knowledge and innovates, does not engage in pre-competition training, and emphasizes the connection between ordinary teaching and practice.

Therefore, over the years, the competition has promoted the implementation of the goal of quality education in physics teaching. In recent years, the reform of the content of the competition has been carried out simultaneously with the curriculum reform of the Ministry of Education, especially in the educational goals of embodying the process and method, emotion, attitude and values. Some of the competition questions have been included as examples in the Physics Curriculum Standards.

The competition has been completed, and the details are available at the test centers in each city and county.

I'll give it to you. There are so many topics...

First question:

Pressure * volume = work.

The charged additional pressure of the sphere can be done using the "virtual work principle".

The electrostatic energy of a uniformly charged ball is: kq 2 2r, which represents the power operation, and the denominator of 2 is because the mutual electrostatic energy is double-counted.

Suppose the ball grows a little longer after stabilization, and the radius of the growth is r, then the corresponding change in energy is: E=kq 2 2(r+ r)-kq 2 2r=-(kq 2 2r 2)* r

The reduction of this potential energy is equivalent to the additional pressure external work: w=p v=p*4 r 2* r

The additional pressure is obtained from e=w, p=kq 2, 8 r 4

The formula is not easy to write, you read carefully and don't read it wrong)

The second question: the problem of elliptical orbit you have to experience and understand again, the elliptical motion of satellites, the earth is not in the center of the ellipse, but in a focal point of the ellipse, a is the major axis, b is the short axis, they should not be confused with r.

If you have any questions, send a message to ask.