Childhood Myth: Why do I forget to recognize a word after just looking at it for a while?

I think everyone had this experience when they were young.

When a word appears in front of you

When the number of times is relatively high

It seems like I suddenly don't recognize you anymore

Why is this?

Q1

Why is the return of the south wind so humid?

by Anonymous

answer:

The return of the south wind refers to the period from winter to spring, when some coastal areas in the south will become very humid. At this time, a lot of water will seep out of the walls and floors of the room, which makes the southerners miserable.

As far as southern my country is concerned, the main reason for this phenomenon is the battle between two major air currents. The humid and hot air currents from the South Pacific and the dry and cold air currents from Siberia become evenly matched after the beginning of spring, and they meet in the Guangdong and Guangxi regions. As the sun's direct point moves north, the humid and hot air currents gradually gain the upper hand. When they rush into the originally dry and cold indoor environment, they will liquefy when they encounter cold air and become small water droplets attached to objects.

But if we compare it with other similar geographical areas abroad, we will find that the return of the south wind in my country is particularly serious. This is due to the majestic Wuling Mountains in northern Guangdong. Without them, the humid and hot air currents from the South Pacific would bravely move northward, bringing at most a few rainfalls to the south. But with the existence of mountains, the humid and hot air currents will be stranded in place for a period of time, during which time people in the south will feel that the climate is getting more and more humid. In addition to conventional dehumidifiers or air conditioners, if you want to learn some non-trivial moisture-proof methods, you can look at reference 3.

References:

What kind of weather phenomenon is "Return of the South Wind", what is the principle of its occurrence, and what are the ways to deal with it?

https://www.zhihu.com/question/314033914

Why didn’t you return to Nantian while in the United States?

https://www.zhihu.com/question/41640942

Soap and mosquitoes: the secret weapon to defeat the "return of the south wind"

https://mp.weixin.qq.com/s?__biz=MzAwNTA5NTYxOA==&mid=2651110987&idx=2&sn=c9d5826d774afb3d631141b49ca33d73&scene=21#wechat_redirect

by Muyu

Q2

Why doesn't a wound spring loosen immediately?

by Hehehe

answer:

This is because there are some mechanisms in the watch that slow down the process of the spring releasing energy, just like the difference between a small ball falling directly from a high place and rolling slowly down a very gentle slope. There are many mechanisms that slow down the release of the spring energy. They are mainly divided into two categories:

One is achieved through a gear system, represented by the sesame chain, which uses the principle of leverage through a cone wheel to change the force arm and thus the torque, thereby achieving a stable output of the spring energy. The sesame chain here can be imagined as a miniature bicycle chain, and the gear structure is also a system composed of miniature gears.

(Copyrighted image from the gallery, no permission to reprint)

One is to realize it in the escapement system, which processes the power from the wheel system in advance and then transmits it to the escapement system, so as to ensure a slow and steady energy output. When the energy is transmitted, the additional spring hairspring absorbs the energy and contracts, and then releases the power due to the elasticity of the metal. Since there is an additional escapement fork control, the output energy becomes stable. Then the weak and nearly constant energy is transmitted to the pointer.

In addition, there are limit pins, special wheel trains and other mechanisms that work together to ensure the slow but nearly constant energy output of the mainspring. In particular, the more constant the energy output, the higher the requirements for craftsmanship and the more accurate the time. This is also the most important reason why the price of mechanical watches can be very high.

by freelance

Q3

Why do we feel like we don’t recognize a Chinese character after looking at it for a long time?

by イリヤ

answer:

Good question. When I was young (fingers were not bald yet) and could read ten lines at a glance, if there were a few words with high frequency in the book, I would often suddenly feel confused while reading, so I had to put the book down and play games (not really).

Staring at a character for a long time and suddenly not recognizing it is called "semantic saturation" in psychology. When we read and recognize characters, after the nerves send the electrical signals generated by the retina to the brain, there are two processes: parsing the character shape and connecting the character shape to the meaning. For example, the "藏" in "藏痴" (zang idi) must first be recognized by the brain as a structure with a grass radical on top and "藏" on the bottom, and then this structure is matched to the pronunciation and meaning of "cáng". Semantic saturation occurs in the process of connecting character shape to meaning. The reason may be that the nerves have been repeatedly stimulated a lot in a short period of time, and the activity has been inhibited. The association from character shape to meaning is blocked, and the reading loses its integrity. Roughly speaking, after staring at "藏" for a long time, the part of the brain responsible for parsing the character shape still realizes that there is a square character with a grass radical on top, but it can't help but think that the grass radical is more interesting than the whole character, so it no longer sends the overall structure of the character "藏" to the part responsible for understanding the meaning. The neurons responsible for semantics can only receive "502 Bad Gateway", so it seems that they don't recognize the character "藏".

Semantic saturation does not only cause trouble in life, it can also be used to overcome speech anxiety. If a person stutters every time he says "藏", then you can let him repeat "藏~藏~藏~" over and over again to paralyze the brain, which can weaken the stuttering caused by speech anxiety when reading "藏".

After reading so much, do you still recognize the word "藏"?

References:

https://zh.wikipedia.org/wiki/%E8%AF%AD%E4%B9%89%E9%A5%B1%E5%92%8C

by Tibetan Chi

Q4

What's up with the banana balls?

by nnn

answer:

I don’t know if there is anyone like me who would be excited for several days if a banana ball was kicked into the goal on the court (although it might be a fraud), but I really know the principle.

The principle of the banana ball comes from the Magnus effect in fluid mechanics: when the angular velocity vector of a rotating object does not coincide with the object's flight velocity vector, a lateral force will be generated in a direction perpendicular to the plane formed by the angular velocity vector and the translational velocity vector. This force will cause the object's orbit to shift [1].

Magnus effect diagram | Science Popularization China

The name of the banana ball comes from this. The arc trajectory of the kicked ball is similar to a banana, and the most representative figure of the banana ball is Beckham!

Banana ball actual combat diagram [2]

In fact, the principle of the banana shot seems very simple, but the key is that the force you exert when your foot touches the ball not only makes the ball move forward at high speed, but also makes the ball rotate rapidly. In addition to the defense of the opposing player in front, you also have to consider the initial direction and rotation speed of the ball, which is very difficult (the answerer can't control it well)! Finally, if you want to play the banana shot well, you must practice more on the field, not just talk about it on paper.

References:

[1] Wang Jie. Research status of Magnus effect[J]. Science and Technology Innovation and Application, 2020(15):12-15.

[Posture] What is the principle of Cristiano Ronaldo's elevator ball? What is the difference between the banana ball and the falling leaf ball?

https://mp.weixin.qq.com/s?__biz=MjM5NzUyNjc0MA==&mid=2650444869&idx=5&sn=8dd6cf27884b142d81860673e1af290c&scene=21#wechat_redirect

by just_iu

Q5

Why is the ice slippery?

by Anonymous

answer

Faraday believed that the pressure exerted by a person standing on the ice surface could lower the melting point of the ice, and part of the water on the ice surface would melt to form a water film to produce a lubricating effect. However, quantitative calculations show that the pressure exerted by a person will hardly lead to the formation of a water film. Let's take a look at the specific calculation process. The thermodynamic process of ice melting into water is described by the Clapeyron equation

The left side of the equation is the slope of the solid-liquid boundary of the water PT phase diagram, L is the latent heat of phase change, which corresponds to the heat absorbed during the stage of "absorbing heat without temperature rise during melting" introduced in middle school physics, and Δv is the change in molar volume before and after melting. For a person weighing 70 kg, even if he stands on one foot on a 50 cm long and 1.4 mm wide ice skate, the pressure exerted on the ice is only about 10⁶Pa. The specific calculation process of the pressure is left to the reader as an exercise as a junior high school physics problem. Therefore, dp=10⁶Pa, and then the latent heat of phase change of water, the difference in molar volume between water and ice, and the melting point of ice at normal pressure T=273.15K are brought in. A little calculation shows that the melting point has dropped by dT=0.07℃. Compared with the temperature of several or more degrees below zero in the north in winter, the change in melting point caused by pressure is really negligible. So this time Faraday was indeed wrong.

Phase diagram of water, source: wiki

Modern scientists believe [1,2,3] that when the temperature is not too low, the surface of the ice layer in contact with the air does not suddenly change from regularly arranged water molecules to air, but there is a semi-molten transition layer. The transition layer has a gradually changing structure, from crystalline ice with neatly arranged molecules to an ice-water mixture, and then to a completely liquid water film. The micro ice particles in the ice-water mixture are connected by weak forces such as van der Waals forces and hydrogen bonds, forming a porous structure that can store liquid water, just like gel beads. The closer to the air, the more disordered the arrangement of water molecules in the transition layer, the more liquid water there is, and the weaker the connection between solid ice crystals, and even micro ice chips and ice particles that can move freely appear in the water film. The micro ice chips and ice particles in the water film act as bearing balls, which convert the macro sliding friction during skating into micro rolling friction. This reduces some of the friction.

Schematic diagram of the transition layer on the ice surface[3]

When skating, the pressure generated by the ice skates acts on the semi-melted ice-water mixture in the transition layer, which releases liquid water like a gel bead being squeezed and burst. This water increases the thickness of the original water film, making the lubrication effect better and further reducing the friction coefficient on the ice surface. In this way, the ice skates can reduce resistance through the transition layer on the surface of the ice layer without directly contacting the crystalline ice layer, achieving smooth gliding.

References:

[1] Rosenberg, R. Physics Today 2005, 58 (12), 50.

[2] Orem, MWJ Colloid Interface Sci. 1969, 31 (2), 278.

[3] Wang Guangzhen, Wang Wenliang, Gao Xin, Zhang Shuyong. Causes of extremely low friction coefficient on ice surface: research progress and model analysis[J]. University Chemistry, 2019, 34(01): 33-38.

by Tibetan Chi

Q6

How to make an astronomical telescope by yourself?

by Maxwell@

answer:

It's simple. Just take off grandpa's reading glasses and stack the two lenses together.

Don't laugh, the earliest telescope was really just two convex lenses stacked together. This is the most classic Kepler refracting telescope.

Refracting telescopes are made by using the refraction of light through lenses, and the main types include Kepler telescopes and Galileo telescopes.

The Kepler telescope is composed of two convex lenses. The optical path diagram is shown below. The light from a distant object is converged by the objective lens and then forms an inverted image near the focus. The distance between the eyepiece and the objective lens is adjusted so that the image falls exactly within the focal length of the eyepiece. At this time, the eyepiece is a magnifying glass that magnifies the image. Finally, the observer will see a magnified inverted virtual image.

Kepler telescope | Image from reference 2

The Galilean telescope replaces the eyepiece with a concave lens. The advantage is that the tube is short and forms an upright image, but the field of view is relatively small.

Another important member of the optical telescope is the reflecting telescope, which is made by using a concave mirror to reflect light, hence the name reflecting telescope. The principle is shown in the figure below. After the light enters the telescope, it is reflected by the concave mirror of the objective lens (the primary mirror in the figure), and an image is formed near the focus of the concave mirror, which is then reflected by the eyepiece (the secondary mirror in the figure) into the human eye.

Image from Baidu Encyclopedia

Of course, it is easy to see far. To see the sky, you need to increase the aperture of the telescope. The larger the aperture of the telescope, the more light it can collect and the stronger its ability to distinguish details. In this regard, reflecting telescopes have more advantages. We can use multiple mirrors to splice into a larger concave mirror. If you want to know more about astronomical telescopes, you can refer to reference 1

Back to the topic itself, if you want to make a telescope at home, a refracting telescope is relatively simple. After all, both magnifying glasses and concave lenses are easier to obtain. With two magnifying glasses, stack them together, align the centers, and then adjust the distance between the two convex lenses to achieve the telescopic function. The higher the magnification of the magnifying glass, the farther you can see. However, if you want to observe celestial bodies in this way, you may have to choose a large or close one. It is more realistic to look at the moon, Venus, Jupiter's satellites, etc., but other things may not work. As for reflecting telescopes, concave mirrors may not be very common. How about grinding a spoon and trying it?

References:

Why can telescopes see distant objects?

https://www.zhihu.com/question/21127623/answer/2224608123?utm_source=wechat_session&utm_medium=social&utm_oi=925658922990305280&utm_content=group3_Answer&utm_campaign=shareopn

Telescope (optical instrument)

https://baike.baidu.com/item/telescope/479223

by Frost White

Q7

How do divers gain angular momentum when they turn in mid-air? Is it the same principle as when a cat turns in mid-air and lands on all fours?

by Yearning for the Future

answer:

Same, yet different

Let's look at a cat first. If you release a cat from a high altitude, it will flip over in 1/8 second and land on all fours. Overall, the cat's total angular momentum is zero and it should not rotate. But a cat is a structured creature after all, so we should disassemble it and look at it.

(Copyrighted image from the gallery, no permission to reprint)

It can be seen that cats usually curl up their upper limbs, and when they stretch their lower limbs, they first turn their upper body, then their lower limbs, and usually their tails turn up at the end. This conforms to the law of conservation of angular momentum, because when the upper limbs turn in one direction, the lower limbs will turn in the other direction. Stretching the lower limbs can increase the moment of inertia and avoid excessive rotation.

Then let's look at diving, figure skating, gymnastics and other sports

After Yuzuru Hanyu pushes off the ground and takes off, he quickly gathers his arms, tightens his legs and keeps them close to the axis of rotation, spins quickly, and then spreads his arms after landing to achieve a stable rotation.

Unlike cats, athletes will actively provide an angular momentum when taking off, and then control the angle of rotation through the shape of their limbs. There are three main factors that affect the athlete's aerial rotation: the athlete's initial posture, movement speed, angular velocity, etc. when taking off or leaving the equipment; the movement control of the limbs in the air; the athlete's own mechanics and physiological functions. In the air, athletes change the body's rotational inertia through limb movements such as bending, swinging arms, and curling up, and adjust the speed of somersaults and rotations, thereby achieving the purpose of controlling the movement posture.

The human body's structure is not as flexible as a cat's, so it is difficult to turn the body quickly to adjust posture like a cat. However, in a space station without gravity, it is possible to quickly adjust the body posture in this way.

References:

[1] Marey,M.

[Director Bi] I modeled and analyzed the action techniques in the Mao movie, and even shot a movie myself.

https://www.bilibili.com/video/BV1Sf4y1S7DB

Cat's aerial rotation and conservation of angular momentum - Liu Yanzhu

https://blog.sciencenet.cn/blog-3452605-1260305.html#:%7E:text=The phenomenon of cats turning in the air shows that any organism in the air, including the human body, can affect the rotation of the whole body with the help of the relative movement of the limbs%E3%80%82. In sports, gymnasts and divers in the air can use the movement of their limbs to complete complex turning and flipping movements%E3%80%82%20In aerospace technology, astronauts in a weightless state can use the movement of their limbs to complete the task of walking in the air%E3%80%82

[4] Hao Weiya, Wang Zhi, Ai Kangwei. Changes in the moment of inertia of athletes during aerial somersaults and rotations[J]. Chinese Journal of Sports Medicine.

[5]Xin Meng. Research on the influence of core stability training on the quality of artistic gymnastics rotation movements[D]. Xi'an Institute of Physical Education, 2016.

[6] China Space Station - First Lesson of "Tiangong Classroom" - 2021

by Minke

#This issue's answering team

Muyu, freelance, Tibetan Chi, just_iu, Shuangbai, Minke, Paarthurnax

Source: Institute of Physics, Chinese Academy of Sciences

Editor: Mu Zi