Weather phenomena such as fog, snow, frost and hail are all related to the change of water. Are they new substances? Fog, snow, frost,

The phenomenon that a substance changes from one state to another is called state change.

The process by which a substance changes from a solid to a liquid is called melting. The process by which a substance changes from a liquid to a solid is called solidification.

The process by which a substance changes from liquid to gas is called evaporation. The process by which a substance changes from a gaseous state to a liquid state is called liquefaction.

The process of changing a substance from a solid state to a gas state is called sublimation. The process by which a substance changes from a gaseous state to a solid state is called sublimation.

There are three states of water: solid, snow and frost, liquid, rain and fog dew, gas and water vapor.

Formation of rain: Clouds composed of liquid water droplets (including supercooled water droplets) are called water clouds. If the conditions for cloud droplets to grow into raindrops are met in the water cloud, and the raindrops have a certain falling speed, then it is rain or Mao Mao rain that falls. Clouds composed of ice crystals are called ice cloud, and clouds composed of water droplets (mainly supercooled water droplets) and ice crystals are called mixed clouds. Ice crystals or snowflakes falling from ice cloud or mixed clouds fall into the gas layer above 0℃, and after melting, they also fall to the ground as raindrops, forming rainfall.

Formation of snow: water vapor in the cloud condenses on the surface of ice crystals, while supercooled water droplets are evaporating, and then ice crystals "adsorb" water vapor from supercooled water droplets. In this case, ice crystals will grow rapidly. Besides, supercooled water is very unstable. If you touch it, it will freeze. Therefore, when supercooled water droplets collide with ice crystals in mixed clouds, they will freeze and adhere to the surface of ice crystals, making them grow rapidly. When small ice crystals grow up, they overcome the resistance and buoyancy of air and fall to the ground. This is snow.

Cloud formation: Clouds floating in the sky are composed of many tiny water droplets or ice crystals, and some are composed of small water droplets or ice crystals mixed together. Sometimes it also contains some big raindrops and ice particles. The bottom of the cloud does not touch the ground and has a certain thickness. The formation of clouds is mainly caused by water vapor condensation.

Fog formation: When the temperature drops and the air is quite humid, then when it cools to a certain extent, part of the water vapor in the air will condense out and become many small water droplets suspended in the air layer near the ground. This is fog. Both it and clouds are caused by temperature drop, and fog can actually be said to be a cloud near the ground.

Dew: Above 0℃, the temperature at which air is saturated with water vapor due to cooling is called "dew point temperature". In warm seasons, when the ground objects are cooled by intense radiation at night, the temperature of the air in contact with the surface of the objects drops, and after it drops to the "dew point", excess water vapor is precipitated. Because the temperature is above 0℃ at this time, these excess water vapor condenses into water droplets and adheres to ground objects, which is dew.

Frost formation: It should be said that the water vapor in the air becomes cold, and the ability of air to carry water vapor decreases. Part of the water vapor condenses into small ice cubes, producing many small ice cubes, which fall to the ground and accumulate continuously, becoming frost.

Formation of hail: In the hail cloud, the strong updraft carries many large and small water droplets and ice crystals, some of which fuse with the ice crystals and freeze into larger ice particles. These particles and supercooled water droplets are transported by the updraft to the water content accumulation area, which can become the hail core. The initial growth core of these hailstones has good growth conditions in the water content accumulation area. After the hail A enters the growth area with the updraft, it collides with supercooled water droplets in the area with large water volume and low temperature, and grows into a transparent ice layer, and then enters the low temperature area with small water volume, where it is mainly composed of ice crystals, snowflakes and a small amount of supercooled water droplets, and the hail adheres to them and freezes to form an opaque ice layer. At this time, the hail has grown up and the updraft there is weak. When it can't support the growing hail, the hail will fall in the updraft and continue to grow through the fusion of ice crystals, snowflakes and water droplets in autumn. When it falls to a higher temperature area, the supercooled water droplets that hit it will form a transparent ice layer. At this time, if it falls into another stronger updraft area, the hail will rise again and repeat the above growth process. In this way, hail grows in transparent layer and opaque layer; Due to the differences in growth time and water content, the thickness and other characteristics of each layer are also different. Finally, when the updraft couldn't support the hail, it fell from the clouds and became the hail we saw.

More physical changes in nature:

1. In summer, "white gas" (liquefaction) will be emitted around popsicles.

2. In the morning, the water droplets on the vegetation (liquefied)

3. In winter, the ice on the glass window (condensation)

4. When iodine is heated at high temperature, the volume of iodine becomes smaller (sublimated).

The mothballs in the suitcase gradually become smaller (sublimated).

6. In summer, the outer layer of water tank will "sweat" (liquefy).

7. Clothes frozen outdoors in winter will also dry (sublimate).

8. The water spilled on the ground soon dried up (evaporated).

I felt cold (evaporated) after swimming ashore.

10, there is a layer of frost on the roof tiles.

1 1, dense fog (liquefaction) in the morning

12, water becomes ice (solidified)

13, molten steel is cast into wheels (solidified)

14, hanging trees in winter in the north (Ninghua)

15. In the cold winter, the snowman becomes smaller (sublimated).

16, Wusong (Ninghua) seen in the snowstorm in South China

17, icicles formed on telephone poles during snowstorm (solidified)