A maglev train is a train that is driven by magnetic levitation (i.e., the attraction and repulsion of magnets). Because the magnetic force of its track makes it float in the air, it does not need to touch the ground when walking, so its resistance is only the resistance of the air. The maximum speed of the maglev train can reach more than 500 kilometers per hour, which is faster than the more than 300 kilometers of the wheel-rail high-speed train. Research on maglev technology originated in Germany. As early as 1922, German engineer Hermann Kemper proposed the principle of electromagnetic levitation and applied for a patent for a maglev train in 1934. After the 1970s, with the continuous strengthening of the economic strength of the world's industrialized countries, in order to improve transportation capabilities to adapt to their economies, the world's first maglev train demonstration operation line, the Shanghai Maglev Train, was built. After completion, it will run from Pudong Longyang Road Station to Pudong International Airport is more than 30 kilometers away and only takes 8 minutes. The Shanghai maglev train is a "normally conductive magnetic levitation type" (referred to as "normally conductive type") maglev train. It is designed based on the principle of "opposites attract". It is a suction suspension system that uses levitation electromagnets installed on the bogies on both sides of the train and magnets laid on the track. The repulsive force generated under the action of the magnetic field makes the vehicle float. up (using the magnetic poles of the same name to repel each other). Electromagnets are installed at the bottom of the train and on the top of the bogies on both sides. Maglev train reaction plates and induction steel plates are installed above the "I" rail and below the upper arm part. Control the current of the electromagnet to maintain a gap of 1 cm between the electromagnet and the track, so that the repulsive force between the bogie and the train balances the gravity of the train. The repulsive force of the magnet is used to float the train by about 1 cm, so that the train is suspended on the track. run. This requires precise control of the current to the electromagnet. The driving principle of the suspended train is exactly the same as that of the synchronous linear motor. In layman's terms, magnetic forces similar to electric motors located on both sides of the track perform repulsion. To meet the needs of development, developed countries such as Germany and Japan have successively begun planning to develop maglev transportation systems.
The compass is a simple instrument used to determine direction. The predecessor of the compass is Sinan, one of the four great inventions in ancient China. The main component is a magnetic needle mounted on a shaft that can rotate freely. The magnetic needle can be kept in the tangent direction of the magnetic meridian under the action of the geomagnetic field. The north pole of the magnetic needle points to the geographical north pole, and this property can be used to identify directions. Commonly used in navigation, geodesy, travel and military. Also sharing the same name is the name of the band and the title of the movie.
China is recognized as the country in the world that invented the compass. The invention of the compass is the result of the Chinese Han working people's long-term understanding of the magnetism of objects. Due to production labor, people came into contact with magnetite and began to understand the magnetic properties. People first discovered the property of magnets to attract iron, and later discovered the directivity of magnets. After many experiments and research, a practical compass was finally invented. The earliest compasses were made of natural magnets, which shows that the Chinese Han working people discovered natural magnets and their ability to attract iron very early. According to ancient records, as far back as the Spring and Autumn Period and the Warring States Period, as we were in the period of great change from slavery society to feudal society, productivity had greatly developed, especially agricultural production, which promoted the mining and smelting industries. industry development. In long-term production practice, people have learned about magnets from iron ore. Guan Zhong's work "Guan Zhong" written in more than 600 BC recorded: "There are magnets on the top and copper and gold on the bottom." It means that if there are magnets on the mountain, there will be iron ore hidden in the mountain. In the famous ancient Chinese geography book "The Classic of Mountains and Seas", it is also recorded that "there are many magnets in the mountains". "Shui Jing Zhu" records that in front of the Afang Palace in the Qin State, a gate was made of magnets to prevent anyone from entering the palace for assassination. If a bad guy entered the palace wearing armor or hiding weapons, he would be attracted by the door and be discovered. This shows that people discovered the iron-attracting properties of magnets very early and took advantage of them. During the long-term production struggle, the Chinese Han working people further utilized the polarity of magnets to create a direction-indicating machine, which is the compass. This is recorded in "Han Feizi Youdu Pian" and "Guiguzi".
It is recorded in "Guiguzi" that when the Zheng people went to collect jade in the deep mountains and forests, they took "Si Nan" with them in order not to lose their way. This "Sinan" is a machine like a compass. Wang Chong of the Eastern Han Dynasty described "Sinan" in "Lunheng". It is like a water spoon.
It is made of natural magnets and ground. The bottom of the spoon is a sphere, the spoon is oval, and the handle is tapered throughout. Shrunk into a columnar shape. In order to determine the direction, there is also a "ground plate", which is a copper or painted wooden plate with a smooth circular groove in the center. The shape may be an inner circle and an outer square. The directional scale is carved on the frame, which is marked with "dry". , "branch" (i.e. A, B, C, D... and Zi, Chou, Yin, Mao...) and Bagua indicate the twenty-four directions. When it is thrown into the center of the land, its handle will roughly stop in the direction of the guide. It can be seen from the above that Sinan is the shape of a modern compass (magnetic compass). "Guide" was first proposed by Zhang Heng in "Tokyo Fu". It was gradually developed after more than a thousand years in the Wei, Jin, Southern and Northern Dynasties, Sui, Tang, and Song Dynasties. Shen Kuo, an outstanding scientist in the Song Dynasty, made a detailed discussion of the development of the compass at that time in "Mengxi Bi Tan". At that time, driven by the development of production and scientific experiments, especially the rise and expansion of navigation and foreign trade, the compass gradually developed. Shen Kuo summarized the four compass installation methods created by working people in practice. The first is the water float method, which floats the magnetic needle on the water for guidance. Although it is relatively stable, it is prone to instability; the second is the nail rotation method, which places the magnetic needle on the nail. It rotates flexibly and is easy to slide off; It is the bowl lip twisting method. The magnetic needle is placed on the edge of the bowl mouth. It can rotate more flexibly, but it is easy to slip. The fourth is the thread spinning method, which uses silk to hang the magnetic needle, which can achieve flexible and stable rotation. He also recorded the method of artificial magnetization, that is, "grinding a needle with a magnet can guide the needle." This artificial magnet is a huge progress. In addition, "guide fish", "dry needle" and "water needle" have also been produced. The two compasses, the dry needle and the water needle, laid the foundation for the basic structural principles of the modern compass (compass needle). In the process of studying the compass, Shen Kuo also concluded and discovered the existence of geomagnetic declination. In other words, the direction indicated by the compass is "often slightly east, not entirely south." This is my country's great contribution to geomagnetism.