However, the contribution of dust can never be erased. If there is no dust in the atmosphere, sunlight will not be absorbed, reflected, scattered and refracted, and the sky will be white, without snow, rain, sunshine and rainbow. Because dust is a hygroscopic particle, without its core, water vapor in the air can't condense and clouds in the sky can't form. Without the cover of clouds, the surface will become dry and barren, and the weather will be either too hot or too cold. Without dust, many harmful rays in the universe will break into the earth's surface without hindrance, posing a fatal threat to human beings and all kinds of creatures.
In addition to these benefits, dust can condense water vapor. Let them become water drops, otherwise, everything will be wet.
Although Dust has many shortcomings, its contribution is endless. It can make the earth get solar energy gently, and it can also make enough condensation nuclei in the atmosphere, increasing the chances of cloud and rain formation. Adjust the surface temperature to make it suitable for the survival and reproduction of life.
Dust is very harmful to computers. Excessive dust may block the CPU fan, make the fan stop running, cause the CPU to overheat and burn out, affect the contact between boards, and may also cause corrosion of the circuit board.
Dust also made Pickering's ten years of hard work go down the drain. After Lovel predicted that there was a Pluto, he observed it for more than ten years and never saw it. It was not until he found Pluto that he remembered that he had been there, but he thought it was a grain of dust.
Lesson 12 of the first volume of the fifth grade, Without Dust, written by Zhou Yuangui. I also talked a lot about dust, so you can have a look! !
[Edit this paragraph] Types of dust
I. Types of dust
Dust can be roughly divided into three types according to particle size:
1. Powder dust
Dust is particles produced by the extrusion of objects and dispersed into the air. Its particle size varies greatly, the big one can be seen by the naked eye, and the small one can only be seen by a high-power microscope. The particle size is generally 1 μm ~ 10 μm, and its shape is irregular, but its composition is the same as before.
2. Condensed solid smoke
Condensed solid smoke is formed in the process of combustion, sublimation, evaporation and condensation. Its particle size is generally 0. 1 μm ~ 1 μm, which is different from dust and has great cohesion. Most of them are gases formed during the melting process of metal substances. After cooling in air, it condenses into solid smoke, and the particle shape is more regular.
Edited on 20 15-02-06
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Dust travel composition 300 words
Dust travel dust is a fine dry powder of soil or other substances, which is converted into a fine part of something; The diameter of fine powder and dust particles is generally between 1% and hundreds of millimeters, which is invisible to the naked eye. Dust is the enemy of human health, so people especially hate it, because it carries many bacteria, viruses and eggs everywhere and spreads diseases. Industrial dust and fiber dust can make workers suffer from various incurable occupational diseases. Excessive dust will also cause environmental pollution, affect people's normal life and work, and induce human respiratory diseases. However, the contribution of dust can never be erased. If there is no dust in the atmosphere, sunlight will not be absorbed, reflected, scattered and refracted, and the sky will be white, without snow, rain, sunshine and rainbow. Because dust is a hygroscopic particle, without its core, water vapor in the air can't condense and clouds in the sky can't form. Without the cover of clouds, the surface will become dry and barren, and the weather will be either too hot or too cold. Without dust, many harmful rays in the universe will break into the earth's surface without hindrance, posing a fatal threat to human beings and all kinds of creatures. In addition to these benefits, dust can condense water vapor. Let them become water drops, otherwise, everything will be wet. Although Dust has many shortcomings, its contribution is endless. It can make the earth get solar energy gently, and it can also make enough condensation nuclei in the atmosphere, increasing the chances of cloud and rain formation. Adjust the surface temperature to make it suitable for the survival and reproduction of life. Dust is very harmful to computers. Excessive dust may block the CPU fan, make the fan stop running, cause the CPU to overheat and burn out, affect the contact between boards, and may also cause corrosion of the circuit board. Dust also made Pickering's ten years of hard work go down the drain. After Lovel predicted that there was a Pluto, he observed it for more than ten years and never saw it. It was not until he found Pluto that he remembered that he had been there, but he thought it was a grain of dust. Lesson 12 of the first volume of the fifth grade, Without Dust, written by Zhou Yuangui. I also talked a lot about dust, so you can have a look! ! [Edit this paragraph] Types of dust 1. Types of dust According to the particle size, dust can be roughly divided into three types: 1. Dust is particles that are produced by the breaking of objects and spread into the air. Its particle size varies greatly, the big one can be seen by the naked eye, and the small one can only be seen by a high-power microscope. The particle size is generally 1 μm ~ 10 μm, and its shape is irregular, but its composition is the same as before. 2. Condensed solid smoke Condensed solid smoke is formed in the process of combustion, sublimation, evaporation and condensation. Its particle size is generally 0. 1 μm ~ 1 μm, which is different from dust and has great cohesion. Most of them are gases formed during the melting process of metal substances. After cooling in air, it condenses into solid smoke, and the particle shape is more regular. 3. Wood, paper, cloth, oil, coal, cigarettes and other organic substances will produce smoke when burning. Its particle size is generally below 0.5 μ m, and dust is a solid impurity with irregular shape, mostly angular and gray, brown, black and other colors, with water absorption. When there is a lot of dust in the air and the relative humidity reaches a certain level, water vapor forms water droplets, so the dust is easily wetted by water and easily absorbs water. Looking at its chemical characteristics, the composition of dust is more complicated, and sometimes it provides acid radicals and metal ions that lead to degradation. Some dust itself is acidic or alkaline, such as sulfuric acid smog, photochemical smog, metal oxides and other particles are alkaline. In addition, the floating dust in the dust is acidic or alkaline because of its small particle size, very large surface area and strong adsorption capacity. Dust often contains substances such as clay, which will absorb moisture in the air or substances composed of archives, make it undergo hydrolysis reaction and decompose viscous aluminum hydroxide. Biological characteristics: Because the spores of mold are small in size and light in weight, they are scattered around with the air and inevitably attached to dust, so dust is an ideal culture medium, breeding ground and disseminator for microorganisms. Microorganisms secrete mildew spots containing enzymes and organic acids during their growth. Therefore, throughout the ages, people have always been' often wiped, not stained with dust'. However, have you ever thought that human beings can't live without dust? If there is really no dust in nature, what kind of situation will we face? The diameter of dust particles is generally between one ten thousandth and one millionth of a millimeter. The dust that the human eye can see is a giant in the dust, and the tiny dust can only be seen under a high-power microscope. The main sources of dust are soil and rocks. After weathering, they split into fine particles. These particles float in the air with other organic particles. Dust will absorb some sunlight and reflect it around, just like countless point light sources. The sunlight is greatly weakened by the reflection of dust, so it becomes soft. If there is no dust in the atmosphere, strong sunlight will make people unable to open their eyes. Interestingly, dust particles also have a "strange temper", which tends to reflect purple, blue and cyan light with shorter wavelengths, and "likes" to absorb other colors with longer wavelengths. The sky we see on the ground is blue because of the high dust content in the lower atmosphere. If there were no dust in the atmosphere, the sky would be white. Most dust is hygroscopic. Water vapor in the air must adhere to dust to condense into small water droplets. In this way, when the water vapor in the air reaches saturation, the dispersed water vapor will adhere? Dust forms stable water droplets that can float in the air for a long time. If there is no dust in the air, everything on the ground will be wet. What's more, there can be no clouds in the sky, and it is impossible to form rain and snow to adjust the climate, so it is impossible for water evaporated from the ground to return to the ground. If there is less and less water on the earth and it dries up completely, living things can't survive. In addition, due to the refraction of sunlight by these water droplets, there will be colorful natural scenery such as sunset glow, idle clouds and rainbow halo from Zhao Hui. If there were no dust in the air, how monotonous nature would be! The role of dust tells us that everything has its two sides.
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The main content of Dust Travel is 50 words in Grade Three?
Dust Journey mainly introduces us to the characteristics, volume, size, source and harm to human health, which makes us realize that in order to be healthy, we must control dust and protect the environment. Dust fills all the spaces around us and can only be seen when the sun shines on the dark room. The amount of dust varies from place to place. Dust also has a great influence on meteorological changes. There are many sources of dust, which may come from nature or cities. Dust can also cause diseases. Nowadays, people are trying to make dust benefit mankind. Extended information "Dust Journey" fragment: Dust is a tireless traveler on the earth, and it drifts with the turbulence of the air. The air around us is almost everywhere, from indoors to outdoors, from cities to villages, from plains to mountains, from deserts to oceans. A truly dust-free space can only be created in the laboratory. Dust is invisible under a clear sky. Only when the sun shines into the dark room through the cracks in the shutters can you clearly see countless dust flying in the air. Of course, big dust can be seen by naked eyes, and small dust is smaller than bacteria and cannot be observed by microscope.
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How to write a composition about dusty travel?
Write casually! !
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Thoughts on dusty travel. Urgent. . .
The wonderful microbial world in American literature, you will be fascinated by it and can't put it down; In music, you will be intoxicated and immersed in it; In terms of technology, you will be surprised and amazed. In the world of microorganisms, it often makes you dumbfounded and full of freshness. Recently, I read a book "Travel of Dust", which made me know more about microorganisms. Next, let me take you to the microbial world! Microorganisms-bacteria can be regarded as "the earth knows everything", and it can be found in every corner of the earth except the big desert and the top of snow-capped mountains. It is sometimes a bad guy, doing damage in the human respiratory tract and doing evil in the nose and throat. Some "bacterial bullies" can also cause some diseases, which is worrying. But as long as you develop good hygiene habits, there will be no disease. They have invaded blood vessels many times, but thanks to white blood cells and antibodies, they can only look at "blood" and sigh. Once the white blood cells and antibodies are insufficient, the consequences are unimaginable. They also wage wars in milk, esophagus and intestinal cavity to compete with humans. Everything has its shortcomings and advantages, and bacteria also have its advantages, such as composition advertisements.
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