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1. Why does the object expand when heated?

When the object is heated, the motion of the molecules that make up the object gradually intensifies as the temperature increases, so that the distance between the molecules increases little by little, and the object becomes expanded from the perspective of the object as a whole.

Also, the expansion rate of an object is determined by the object itself, and the expansion rate varies from substance to substance.

2. Why do the stars twinkle and twinkle?

We see the stars shining, not because of a change in the luminosity of the stars themselves, but because of the occlusion of the atmosphere.

The atmosphere is separated from us and the stars, and when starlight passes through the atmosphere, it is affected by the density and thickness of the atmosphere. The atmosphere is not absolutely transparent, and its transparency varies depending on the density. So if we look at the stars through it on the ground, we will see that the stars seem to be flickering.

3. Why is most of the sea water blue and green?

When you look at the sea, you can often see that the water is blue and green. However, when you scoop up the seawater, it is transparent and colorless. It turns out that the sea water itself is not much different from the water we come into contact with every day, and it is also transparent.

The blue and green colors we see are actually phenomena produced by the ability of seawater to absorb light. Only green light can be absorbed by seawater and thus reflected; When the water is deeper, the blue light is also absorbed, and the water looks blue. <>

<>1. Why does milk have a layer of skin after heating?

The skin that floats on the surface of the milk is coagulated protein. Milk contains all the essential nutrients for the growth and development of cattle, and protein is one of the very important nutrients.

Proteins solidify once they are heated. The reason why hard-boiled eggs will solidify is because of the eggs.

of the protein coagulated. The proteins in milk also coagulate due to heating.

Proteins, especially those of milk, can coagulate as soon as they go bad, even if they are not heated. Protein.

When spoiled, acid is produced, which causes the milk to coagulate. Yogurt coagulated with lactic acid bacteria can be eaten, but it is better not to eat milk that has spoiled and curdled because it is not known what kind of bacteria can cause disease in it.

2. What are matches made of?

There are two kinds of match rods: paper and wood, and wooden match rods are generally made of five or six kinds of firewood such as poplar and walnut. In the round head of the match, it contains potassium chlorate, potassium dichromate, iron oxide, sulfur, rosin, manganese dioxide, antimony sulfide, etc., and sometimes some lead monoxide is also appropriately added. In order to facilitate the burning of matches, the rod next to the round end of the match is also coated with 1 cm long paraffin.

On a paper matchstick, this part is seen more clearly. The friction surface of the matchbox is coated with red phosphorus, antimony oxide, and sometimes manganese dioxide, silica sand, etc., which are the ignition agents. On the friction surface of the matchbox, press the match and slash it, and the red phosphorus on the friction surface burns first.

This heat causes the other oxidants to emit oxygen in an instant, and the paraffin on the rod is ignited, and the matchstick burns smoothly.