Why are some clouds black?

 Clouds are visible droplets or ice crystal aggregates composed mainly of water in the atmosphere and also contain a variety of other relatively small amounts of chemical substances. We can see clouds because water molecules gather around the dust (condensation nuclei) in the air. They scatter sunlight in all directions, allowing us to see the appearance of clouds clearly.

The size of small water droplets and small ice crystals in the cloud is larger than the wavelength of the incident light, so light of various wavelengths in the sun is scattered by these water droplets and ice crystals to make the cloud appear white. Of course, this is all when the clouds are thinner.

If the cloud is thicker, the sunlight will not show through the cloud, and most of it will be absorbed. At this time, the cloud will look gray and black.

Why does it take longer to urinate when drinking?

Because when you are drunk, it takes longer to urinate. Many people think that alcohol has a diuretic effect, but this view is wrong. Due to the effect of alcohol, our ability to feel the bladder becomes dull. Generally speaking, when the bladder reaches 200cc, we will want to go to the toilet. But when you are drunk, your bladder reaches its maximum limit and you still can’t feel the urge to pee. The capacity of an adult’s bladder is about 400-500cc. Therefore, when you are drunk and want to go to the toilet, your urine volume must be twice as much as usual. It also becomes longer.

Why is the sea so "blue" so charming?

Sunlight is composed of seven colors of red, orange, yellow, green, cyan, blue, and purple. The absorption of light by sea water is related to the wavelength of light. Long-wave light (red) absorbs faster, and short-wave light (blue) absorbs slowly. When sunlight hits the deep ocean below a hundred feet, only a piece of blue light remains, and other colors of light are absorbed. Therefore, The sea reflected in the eyes is so blue that it is so charming. Moreover, the deeper the sea, the stronger the blue.

Why do animals’ knees bend backwards?

Human knees are undoubtedly bent forward, but for some animals, such as cats, dogs, cows, horses, and birds, their "knees" seem to be bent backward.

In fact, those animal "knees" that you think are bent backwards are not knees at all.

The bones in the human thigh and calf are called "femur" and "tibia" respectively. For animals such as cows, what you think of as the "thigh" is actually the "tibia", so it should correspond to our calf. And their real thighs, the "femurs" are located above the tibia, closer to the hip area, so the real knees are hidden very close to the body. The same goes for chickens and ducks. The "thighs" you usually eat are just their calves.

Those structures that we mistake for "knees" are actually equivalent to our ankles, and the so-called "calves" below are part of the soles of the feet.

In addition to humans, what other animals shed tears?

Speaking of animals that shed tears, they have been more or less found in all terrestrial species of the vertebrate subphylum. This is actually a very normal phenomenon. Animals "tear", sometimes to moisten the eyes and provide nutrition to the cornea; sometimes because of eye inflammation or infection; sometimes to remove foreign bodies, etc.

But in our human worldview, tears always carry some emotional color, so when you see other animals "tear", there will always be comments like "all things are alive". But in fact, some scholars believe that only humans shed tears because of emotions, especially human sobbing or weeping, which basically does not happen subjectively in animals.

 

Although some scholars believe that many animals have sad emotions, in the natural environment, if animals cannot hide their emotions, letting tears blur their vision or sobbing will increase the risk of predation.

Why are there no square celestial bodies?

Whether it is planets, stars, or other celestial bodies, they are often spherical or nearly spherical. Why hasn't a square celestial body been discovered? This starts with the formation process of celestial bodies.

Celestial bodies will capture surrounding dust, gas and other materials during their formation. This process is called "accretion." In the early stage of formation of a celestial body, collisions and fusions with various substances will make it form a crooked irregular shape, but as the mass of the celestial body increases, the effect of gravity begins to become stronger, and some prominent edges and corners will collapse due to their own gravity. Melt into the celestial body, and finally form a stable sphere or sphere-like shape.

The only natural square objects in the universe are crystals, such as pyrite. But their volume is much smaller than that of celestial bodies.

How does the plane land in Antarctica?

We know that even a car is difficult to drive on a road that is frozen by ice and snow, let alone a large aircraft that requires precise control? But mankind has indeed overcome this difficulty and built the airport to Antarctica in the icy and snowy land.

There are two main types of airport runways in Antarctica: land-based rock runways and ice-snow runways. The former is no different from an ordinary airport runway, which is a pavement constructed of rock and cement; while the latter is compacted by ice and snow. Such a runway requires special machinery and equipment to ensure that the road is flat and solid and can generate sufficient friction.

 

The Antarctic continent has a very limited area suitable for building an airport, and the wheeled aircraft we usually take have very strict requirements on the runway. Therefore, most of the aircraft types are small and medium-sized aircraft equipped with skid landing gear. In order to flexibly respond to the transition between land and snow runways, aircraft on the Antarctic route are generally equipped with convertible take-off and landing wheels and sled board landing gear. However, it is very difficult to take off with the skid-board landing gear, and booster rockets are used to increase speed when necessary.