Children's popular science knowledge I
The invention of false teeth
Dental caries has always been a problem. Around 700 BC, Etta Lasquin in ancient northern Italy made false teeth out of gold. But until the18th century, teeth of this texture were still rare. It is very difficult to make teeth that are completely suitable for patients, and the upper denture often falls off. Sometimes wearing false teeth is almost as bad as tooth decay itself.
In order to prevent the upper teeth at the top of the mouth from falling off,18th century, a Parisian dentist named Fouchard first made dentures with steel springs. But even as far as these springs are concerned, they are rarely properly installed, and the traditional tooth-making material ivory will soon deteriorate and there will be an unpleasant smell in the mouth.
/kloc-In the late 8th century, French dentists introduced porcelain. The whole upper and lower rows of teeth can be molded from a whole piece of porcelain. This makes a set strong and durable, but they are still uncomfortable. Right: After design, modern dental technicians can make dentures that are very similar to natural teeth and can be used to replace natural teeth. These dentures are well assembled and comfortable to wear.
Until 65438+1940s, wearing dentures was still uncomfortable. Then, in 1844, American hardware dealer and inventor Charlie goodyear announced a new hardened rubber structure called hard rubber. When making oral impression of patients, the hard rubber mold can be cast into a comfortable matching bottom plate for installing dentures. Finally, people can wear comfortable and durable dentures.
In order to make dentures very suitable for use, teeth should be accurately printed in the patient's mouth. The first person to do this may be a Frenchman, Dubois de Chemante, who put wax in the patient's mouth to make an impression.
The invention of abacus
Abacus is a common calculation tool. Who is the inventor of abacus? What is the exact year of invention? We first saw the word "abacus" in Xu Yue's book Numerology Legacy in the Eastern Han Dynasty. However, the note says that only addition and subtraction can be done. Today, it seems that this theory is the embryonic form of an abacus. From the analysis of available reliable data, abacus was invented in Song and Yuan Dynasties. People have consulted a lot of historical documents, but they can't find the name of the inventor of the abacus. This of course shows that feudal rulers did not pay enough attention to scientific and technological inventions. On the other hand, it also shows that their invention is a step-by-step process, which is gradually improved and perfected. It's hard to say which is responsible.
Due to the development of society, the speed and accuracy of calculation are increasingly demanding, so people have reformed the earliest used algorithms and created various songs. For example, the song of 14+7 is "Seven divided by three is one". All addition, subtraction, multiplication and division have a set of songs. In fact, before the abacus appeared, almost all the abacus rhymes were ready except for a few division rhymes. After melody appeared, the calculation speed was improved. In this way, abacus instead of calculation has become an inevitable development trend, not only the conditions have been met, but also a very urgent matter. It was in this situation that craftsmen, calculators and businessmen at that time worked together to develop a sophisticated abacus.
The abacus is one of China's great scientific achievements in ancient times. It has the advantages of simple structure, simple operation and convenient carrying, so it is widely used and lasts for a long time. After China showed his talents, abacus calculation spread to Korea, Japan, Southeast Asia and Arabia, and made great contributions to world civilization.
The invention of handball
Handball is a ball game, which can be played indoors and outdoors. It combines many characteristics of basketball and football, so it is very popular. Handball first appeared in Europe. Legend has it that in 1898, a European football player injured his right foot in the game and could never play football again. So he was very upset, so he came up with the idea of using hands instead of feet to complete football action and created handball. At first, handball was an outdoor sport, and the competition system was 1 1. Players wear football shoes, and only 6 players are allowed to take part in the offense and defense, and they can dribble continuously without restriction. 19 17 officially organized the competition in Germany. Since then, handball has become popular in Europe. Handball was officially included in 1 1 Olympic Games in 1936.
What you must know about popular science II
What metal minerals are there in the stratum?
Metal minerals refer to rocks that can extract a certain amount of metals. In nature, only gold and copper exist independently, and they are not combined with other elements. In addition, most metals are extracted from ores. The earth provides us with many metal minerals, such as common copper and iron. By refining these minerals, we can get metals. Metal is an indispensable material in human production and life, while the reserves of gold, silver, platinum and other metals in the earth's crust are very small, also known as precious metals. They are the main materials for making ornaments, and the price is usually more expensive.
How are minerals formed?
Minerals are natural simple substances or compounds formed by geological processes. At present, there are more than 3,000 known minerals on the earth, but only more than 50 are the most common. Minerals are formed under certain physical and chemical conditions. When the external conditions change, the original minerals can change and form new minerals. The formation of minerals includes three forms: gas to solid, liquid to solid and solid to solid. The most common form from gaseous state to solid state is hydrogen sulfide gas ejected from volcano to form elemental sulfur, while liquid state to solid state is salt minerals formed by evaporation and crystallization in salt lakes, and solid state to solid state is mainly amorphous to crystalline minerals.
Where does the oxygen come from?
The existence of life is thanks to cyanobacteria, which completely changed the earth's atmosphere. They discharged oxygen as waste, making the earth's atmosphere full of oxygen for the first time 2.4 billion years ago. However, rock evidence shows that in the past 3 billion years, the oxygen level increased and decreased rapidly like a roller coaster, and gradually stabilized until 54.48 billion years ago in Cambrian. Are bacteria contributors to oxygen in the earth's atmosphere? Or are there other influencing factors? Understanding how the oxygen-enriched atmosphere is formed is a key factor to decipher the history of life development on earth.
Do you know what the solar wind is?
During the total solar eclipse, a circle of pale yellow light will appear on the surface of the black sun. This phenomenon is called corona. The corona extends millions of kilometers from the surface of the sun. The corona consists of gases as high as 65438+500,000℃.
The charged particles (positrons and electrons) that form the corona flow around the earth at a speed of 500 kilometers per second. This is the so-called solar wind. The solar wind also circulates around the earth at 200,000 ~ 300,000 degrees Celsius, and it is very terrible because it is a stream of charged particles. Fortunately, the earth's magnetic field acts as a barrier to protect the earth from the influence of the solar wind.
Because the earth is a magnetic field, the charged particles of the solar wind surround the earth, thus forming a strong radiation belt, which is the Van Allen radiation belt.