Exchange of scientific knowledge

Exchange of scientific knowledge

The solid body has vanished into thin air! The liquid was gone, and it was also in air! How do they do it?

Volatile and evaporation:

Evaporation means that molecules of a substance freely radiate around themselves, move freely and are not affected by temperature. It can be liquid or solid.

Evaporation usually means that liquid components are converted into gas molecules and leave surface of liquid before reaching boiling point. Most solutions are volatile because their intermolecular attraction is relatively small and they are in constant random motion. So their molecules move into air and slowly evaporate. However, due to different solutes, volatility is different.

The process of phase transition of water from a liquid or solid state to a gaseous state. Evaporation and boiling are phenomena of evaporation and are two different ways of evaporation. Evaporation is a process of vaporization that occurs on surface of a liquid, and boiling is a phenomenon of rapid vaporization that occurs simultaneously inside and on surface of a liquid[

Evaporation is a physical change in which water molecules in a liquid change from a liquid state to a gaseous state due to random motion. Evaporation can occur at any temperature, higher temperature, higher evaporation rate.

Evaporation is also a physical change. This is free distribution and movement of molecules of a substance, which does not depend on temperature. It can be liquid or solid. Volatile substances usually refer to organic substances such as alcohol, gasoline, camphor, etc.

Children should watch drying of clothes, disappearance of alcohol, etc. carefully! ! !

What is ice and what is frost?

Frost formation:

Frost refers to white ice crystals formed by sublimation on ground or objects when air near ground cools below freezing (i.e. dew point below 0) due to effect of radiative cooling of ground. . Frost is a weather phenomenon that belongs to content of China's surface meteorological observations. "Frost" usually appears in autumn-spring period. In meteorology, first frosts that occur in autumn are usually referred to as "early frosts" or "first frosts", and last frosts in spring as "late frosts" or "last frosts". period.

"Hoarfrost" does not descend from sky. "Hoarfrost" is formed as a result of condensation of water vapor on ground in cold weather. Frosts occur in autumn, winter and spring. Hoarfrost is formed when water vapor condenses in air near formation directly on ground or objects near ground; lower temperature, greater density of air and greater specific gravity. With flow of air, coldest and heaviest air will enter lowest point, and when it reaches lowest point (depression), it will gradually accumulate and condense into frost. Therefore, frosts form more often in depressions than in ordinary places, and plants in depressions are especially vulnerable to frost.

Children, ice and frost are not same thing, you must clearly distinguish between them! ! !

The opposite is you, and it seems that you are not yourself, but he is really you!

Strange mirror:

A mirror is an object with a smooth surface and ability to reflect light. Originally, ancients used polished bronze as a mirror. There are two types of flat mirrors and curved mirrors. Flat mirrors are often used by people to organize their appearance. Curved mirrors are divided into concave mirrors and convex mirrors. They are mainly used as clothing mirrors, furniture accessories, architectural decorations, optical instrument accessories, solar panels, reflectors for car headlights and spotlights, reflecting telescopes, car rear-view mirrors, etc.

In science, mirrors are often used in telescopes, lasers, industrial equipment, and other instruments. Surface polished metal instruments with regular reflective properties and glass or metal products coated with reflective metal films are often encrusted with metal and plastic or wood edging. .

Mirror is principle of reflection. A mirror is an object with a smooth surface and ability to reflect light. Whether it is a flat mirror or a non-planar mirror, light obeys law of reflection and is reflected by mirror. After reflected light enters eye, it can form vision on retina. On a flat mirror, when a beam of parallel rays hits mirror, everything changes its direction in a parallel pattern, and image at that time is same as what eyes see.

Do children see themselves same way when they look in mirror? Then watch yourself in a mirror without light! ! !

As they say, water and fire must be irreconcilable, so who can't stand whom?

Water and fire are incompatible:

The presence of combustibles, flash point temperature, and sufficient contact with oxygen are three main elements of a fire. Due to large specific heat of water and a large amount of sufficient water, it can also play role of oxygen isolation, and can quickly lower flash point temperature, so effect of using water to extinguish a fire is very significant. .

Combustible substances are fully exposed to hot surface, electrical heating wires, small ignition sources in radiant energy (such as medium electrical spark discharge) can cause fire, heat capacity and heat of vaporization of water is relatively large, water can absorb a lot of heat from burning material and reduce temperature of burning material. When water meets a burning material, its temperature rises and it turns into water vapour. It takes 539 kcal to convert 1 kg of water into water vapor. Because water can absorb such a large amount of heat when evaporating, spraying water on surface of burning material can quickly lower surface temperature of burning material, and play a role in cooling and cooling, which is beneficial for fire. extinguishing.

Water evaporates to form water vapor, which can prevent air from entering combustion zone and reduce oxygen content of air in combustion zone so that it can contribute to ignition and extinguishing. Water can dilute some liquids, dilute concentration of combustible gases in combustion zone, reduce intensity of combustion, and can also soak unburned substances, making them difficult to burn. Water has a mechanical effect. The flow of water strongly affects flame, as a result of which the flame is interrupted and extinguished.

Do you understand, children? ! ! While water can put out a fire, not all fires can be put out with water! ! ! For example, water can not be used for a burning oil pan, children must remember! ! !

Strange cup:

In winter or when temperature is very low, pour boiling water into a glass. Preheat glass with a little boiling water to prevent temperature difference between inside and outside of glass from becoming too large. thermal expansion of inner wall is prevented by outer wall to generate force, causing glass to break.

This is caused by large temperature difference between inside and outside of glass. When boiling water is poured into a glass, inner glass immediately expands when heated, but outer wall of glass is colder and stays same. Thus, inner glass will be desperately squeezed out, and glass will be broken and burst. After preheating with a small amount of boiling water, and then pouring boiling water over glass, glass will not break.

Expansion on heating and contraction on cooling refers to characteristic that an object expands when heated and contracts when cooled. Because movement of particles (atoms) in an object changes with temperature, as temperature rises, particle vibration amplitude increases, causing object to expand, and as temperature decreases, particle vibration amplitude decreases, causing object to shrink. Substances such as water (below 4 ° C), antimony, bismuth, gallium, bronze shrink when heated in a certain temperature range and expand when cooled, which is directly opposite to properties of ordinary objects.

Children should follow safety rules when drinking hot water in winter, especially when wearing glasses! ! !

The glass is broken, but nobody touches it, what's going on?