maglev train
The induction plate and the induction steel plate control the current of the electromagnet to keep a gap of 1cm between the electromagnet and the track, so that the repulsive force between the bogie and the train is balanced with the gravity of the train, and the train is suspended about 1cm by the repulsive force of the magnet, so that the train can run on the track. This must accurately control the current of the electromagnet. The driving principle of suspension train is exactly the same as that of synchronous linear motor. Generally speaking, the magnetic forces similar to motors repel each other on both sides of the track. In order to meet the needs of exhibitions, Germany, Japan and other developed countries have begun to plan and develop maglev transportation systems.
Compass is a simple tool to judge the direction. The predecessor of compass is Sina, one of the four great inventions in ancient China. The main component is a magnetic needle that can rotate freely on the shaft. The magnetic needle can be kept in the tangential direction of magnetic meridian under the action of geomagnetic field. The north pole of the magnetic needle points to the geographical north pole, which can be used to identify the direction. It is often used in navigation, geodesy, tourism and military affairs. There are also band names and movie names of the same name.
China is regarded as the country that invented the compass in the world. The invention of the compass is the result of the working people of Han nationality in China's long-term practice in understanding the magnetism of objects. Due to productive labor, people came into contact with magnetite and began to understand its magnetism. People first discovered the property that magnets attract iron, and later discovered the directivity of magnets. After many experiments and studies, a practical compass was finally invented. The earliest compass was made of natural magnets, which shows that the working people of Han nationality in China discovered the attraction of natural magnets and their iron very early. According to ancient records, as early as the Spring and Autumn Period and the Warring States Period, the productive forces developed greatly, especially agricultural production, which promoted the development of mining and smelting industries. In the long-term production practice, people know magnets from iron ore. In Guan Zhong's book "Guan Zhong" more than 600 years BC, it is recorded: "There are magnets in the world. There is copper and gold under it. " It means that if there is a magnet on the mountain, there is an iron ore hidden in the mountain. In Shan Hai Jing, an ancient Chinese geography classic, it is also recorded that "there are many magnets in the mountains". It is recorded in the Notes on Water Classics that the front of Epang Palace in Qin State is made of magnets to prevent people from entering the palace to assassinate. If the bad guys wear dark armor and take hidden weapons into the palace, they will be caught in the door and found. This shows that people have long discovered the iron attraction of magnets and used it. In the long-term production struggle, the working people of Han nationality in our country further used the finger polarity of magnets to make a machine to indicate the direction, which is the compass. This is recorded in Youdu Pian and Guiguzi. It is recorded in Guiguzi that when Zheng people went to the deep forest to collect jade, they brought "Sina" in order not to get lost. This "Sina" is the mechanical compass. Wang Chong in the Eastern Han Dynasty described "Sina" in Lun Heng, just like a water spoon.
Made of natural magnets, the spoon bottom is spherical, the spoon body is oval, and the handle gradually shrinks into a column. In order to determine the direction, there is also a "place", which is a copper or painted wooden board with a smooth circular groove in the middle, which may be outside the inner ring. The rack is marked with azimuth scale, and 24 orientations are represented by "stem" and "branch" (namely, A, B, C, D, Zi, Ugly, Yin and Mao, etc.). ) and gossip. When it will be thrown in the center of the field, its handle will usually stop in the direction of the guide. As can be seen from the above, Sina is in the shape of a modern compass (magnetic compass). "Dao" was first put forward by Zhang Heng in "Tokyo Fu", which developed gradually through Wei, Jin, Southern and Northern Dynasties, Sui and Tang Dynasties, and lasted for more than 1000 years in the Song Dynasty. Shen Kuo, an outstanding scientist in the Song Dynasty, made a detailed discussion on the development of the compass at that time in Meng Qian 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 four installation methods of compass created by working people in practice. The first is the water float method, in which the magnetic needle floats on the water for guidance. Although relatively stable, it is easy to be unstable. The second method is nail rotation, and the magnetic needle is placed on the nail, which is flexible to rotate and easy to slide down; The third method is that the bowl lip rotates, and the magnetic needle is placed on the edge of the bowl mouth, which is flexible to rotate but easy to slide down; The fourth method is the spiral method, which can realize flexible and stable rotation by hanging the magnetic needle with silk thread. He also recorded the method of artificial magnetization, that is, "grinding a tit with a magnet can guide you." This artificial magnet is a big step forward. In addition, there have been "guiding fish", "dry needle" and "water needle". Dry needle and water needle laid the basic structural principle of modern compass (compass needle). In the process of studying the compass, Shen Kuo also found the existence of magnetic declination. In other words, the direction indicated by the compass is "always slightly east, not completely south". This is China's great contribution to geomagnetism.