Shulou(Shulou.com)11/24 Report--

How is tempered glass made?

Why, after it was smashed,

Will crack on the inside first.

And the outside is still intact?

Q1. The principle of atomic bomb explosion is nuclear fission. How is the process of nuclear fission ignited? By Meow

A:

Nuclear fission exists all the time, and it is the continuous chain reaction that needs to be ignited.

Nuclear fission is an inherent property of the nucleus. The nucleus of a radionuclide may decay into other nuclei and release energy all the time. If the nuclear decay concentration is reduced to half of its initial concentration over a period of time, then this period is called the half-life of this radionuclide. Take the most famous uranium-235 as an example, one of its main decay paths is fission into barium-141 and krypton-92 after capturing one neutron, and releasing three neutrons. This process releases a lot of energy. If all three neutrons released can bind to one uranium-235 respectively, the reaction will expand exponentially, and the heat will accumulate rapidly, becoming the energy source of the nuclear explosion. The whole process is called the "chain reaction". But if the number of uranium-235 atoms is not enough, neutrons may not be able to hit the uranium nucleus, leading to the termination of the chain reaction. In order to ensure the continuity of the reaction, it is necessary to ensure the minimum amount of uranium lump-critical mass or critical volume. The uranium lump below this critical value cannot keep the chain reaction going. The actual atomic bomb is to separate two pieces of uranium with a volume greater than half of the critical volume and less than one critical volume, and coat the periphery with a layer of TNT explosive. When detonating, TNT is detonated, and the shock wave pushes two uranium blocks together to form a new uranium block whose volume is larger than the critical volume. At this point, the chain reaction can be carried out continuously.

By Jing Yun

Q2. Why is it that after I dig up a spoon of protein powder with a spoon of protein powder, the outer surface of the spoon will have spines like a hedgehog?

By Xiao Li doesn't stay up late.

A:

Seeing this picture reminds the editor of the phenomenon that often occurs on spoons when weighing powdered medicines in the drying room.

This phenomenon in the picture is actually caused by static electricity. Generally speaking, in order to ensure the quality of this kind of edible protein powder, the manufacturer will make the tank as dry as possible to avoid damp deterioration of the powder. While the plastic spoon in the use process will experience a variety of friction, in such a dry environment, the spoon is easy to bring electricity. Powdered solids are easily attracted because of their light weight, so they "stick" to the spoon in this way. As for why it is like a hedgehog, it is because the powder is polarized by the electric field of the charged body, which is similar to the feeling of using iron shavings to simulate magnetic induction lines shown in physics textbooks.

By Eric

Q3. Why does the toughened glass look cracked after smashing, but in fact the surface is intact? By cesium atomic clock

A:

Tempered glass is made of ordinary glass through a heat treatment process, which is called "tempering". The strong stress produced by tempering makes the surface of the glass under pressure and the interior of the glass under tension, so the stiffness and toughness of the glass are greatly enhanced. After the physical toughening of the glass, near the softening point and quenched by the medium, the compressive stress is formed on the glass surface and the tensile stress is formed inside the glass, which improves the tensile performance of the glass surface, and the strength of the glass is greatly improved. the balance between the surface compressive stress and the internal tensile stress. When the glass is impacted by external forces, the impact energy is greater than the internal energy, and the glass is broken. Under the action of internal energy, the glass is destroyed into sharp-angle fragments.

The important characteristic of toughened glass [1] is that it will defend itself when it is impacted. The reason is that there is tensile stress in the toughened inner layer (the reaction force of the object to the external force that causes the object to have a tensile trend). When the glass is broken, under the protection of the compressive stress of the outer layer (the stress of resisting the compression trend of the object), the glass becomes an aggregate full of cracks, but it is not easy to scatter, and the fragments are honeycomb-like obtuse particles. The harm to the human body is reduced to a minimum.

Reference:

[1] [Science Popularization] self-explosion characteristics of tempered glass and its judgment-Zhihu

[2] theoretical analysis and experimental research on the safety performance of toughened glass-China knowledge Network

[3] Analysis of morphological characteristics of cracks in physically toughened glass-China knowledge Network

By floor sweeping monk

Q4. Why does the solution formed after hydrogen chloride dissolves in water have the name "hydrochloric acid"? By Anonymous

A:

Drop a book bag first. The Chinese name of hydrochloric acid can be traced back to the New compilation of Bowu compiled by British missionaries in 1855, in which hydrochloric acid is called "salt strong water", in which "strong" and "strong" water means strong acid. Until 1932, the government of the Republic of China issued the principle of Chemical Nomenclature, confirming that the aqueous solution of HCl was called hydrochloric acid. Thus it can be seen that the evolution of the Chinese name of hydrochloric acid all originated in modern times and was naturally greatly influenced by the West. Therefore, if you want to find the origin of the word "salt", you should explore the source of the word "salt" in English.

Hydrochloric acid has an alias muriatic acid in English, meaning "acid related to salt". This is probably the source of the Chinese translation of "salt". European alchemists / chemists in the 13th century (equivalent to the Southern Song Dynasty / Yuan Dynasty) made aqua regia-now we know it contains hydrochloric acid and nitric acid. In the 15th and 17th century (Ming Dynasty in China), a series of European chemists isolated pure hydrochloric acid. The methods they use include heating after mixing salt with sulfuric acid, heating after mixing salt with sodium sulfite, and so on. It can be found that there is salt in all the raw materials, which is probably the origin of the name "hydrochloric acid".

By Jing Yun

Q5. Why is it that when the room window opens, no matter whether there is wind outside or not, the door will be easily closed with very little force? By chenchen

A:

Because when the room window is closed, the gas exchange between the room and the outside world can only be carried out through the door. When the door closes, the door will squeeze the air in the dotted area into the outside world, resulting in a reduction in the total amount of air in the house and the air pressure is lower than the external atmospheric pressure. This creates a pressure difference pointing to the house on the inside and outside of the door, which will hinder the closing of the door.

When the window of the room is opened, the gas in the room can be exchanged with the outside world through the window, so the air discharged from the door will be supplemented by the air in the window, and the air pressure in the house is basically equal to the atmospheric pressure. In this way, when we close the door, we only need to overcome the air resistance of the door and the friction of the bearing, so that we can easily open and close the door.

By single male youth

Q6. What substance is jade? Can you write down the chemical formula of it (or the substances that make up it)? By cesium atomic clock

A:

Jade is a widely used word that can be used to refer to a series of hard and dense stones ranging from white to green. According to mineralogists or geologists, jade is the general name of two different kinds of minerals, which are jadeite (or jadeite) and Hetian jade (or nephrite).

The main composition of jadeite is that it can contain Cr, Fe, Ca, Mg, Mn, V, Ti and other elements. It may also contain other mineral components such as sodium and sodium-calcium pyroxene (such as omphacite, sodium chromopyroxene) and so on.

Hetian jade is mainly composed of tremolite and actinolite.

The difference is that tremolite contains more magnesium.

While actinolite contains more iron.

.

If jade is strictly limited to jade and Hetian jade, the works of many ancients who are traditionally thought to be carved with jade will no longer be jade. In fact, the national standard of Jewelry and Jade Identification in China classifies 40 kinds of minerals (including malachite, Dushan jade, serpentine, etc.) as natural jade.

Reference:

[1] GB / T 16553-2017, jewelry and jade identification [S].

[2] Rawson J. Chinese jade [M]. London: British Museum Press, 1995.

By has a bright future.

Q7, how many combinations are there in license plate number? By is an inquisitive little blue.

A:

You might as well make an estimate.

According to the current 92 civil license plate rules, excluding military and police, emergency, coaching, towing, embassy and other special license plates, ordinary civil fuel vehicle license plate (blue card, yellow card) a total of 7, new energy vehicle license plate a total of 8. The first two are code names, which are provincial unit codes plus license issuing authority codes. A total of 418 kinds can be obtained by simple counting [1]. The last five digits (or six digits) are called serial numbers, which enlarge the letters for the numbers so that they can be easily identified, without the letters I and O. The five-digit serial numbers of blue and yellow cards have at most 2 letters, so they are species. [2]

Fuel license plate rules | Source: GB36-2018 [2] New energy vehicle license plate rules are complicated, which can be divided into large cars and small cars. The letters of large cars are in the sixth place of the serial number and those of small cars are in the first place-these differences do not affect the number. At present, the letters of pure electricity can choose D, A, B, C, E, and non-pure electricity can choose F, G, H, J, K. The other five digits of a large car are numbers, and the second serial number of a small car can be a number or a letter-also excluding I and O, so there are currently = kinds of new energy license plates, so there are a total of 2951080000,919600000,3870680000 fuel vehicles and new energy license plates.

Small new energy license plate rules | Source: GB36-2018 [2] in addition to Yu A license plate, Zhengzhou also adds Yu AA license plate, which will lead to a slight reduction in the total number. In the future, with the increase of car ownership and changes in administrative divisions, some cities will add license plates, such as Wuhan has added Hubei W, Jinan merged with Laiwulu S and so on. The total number of license plates will still change.

Reference:

[1] license plate number

[2] GA38-2018 vehicle license plate of the people's Republic of China

By Jing Yun

Q8, why sometimes the human voice is enhanced when headphones are turned on in noise reduction mode? By, a young man of old age.

A:

This question is very interesting, so let's learn about headphone noise reduction with this student today.

First of all, noise is a very subjective term. It can refer to any unpleasant sound that people do not need at a certain time. From a physical point of view, there is no difference between noise and the sound we "want". It is a vibration wave generated by a medium such as air. The two main indicators of a sound wave are amplitude and frequency. The amplitude describes the intensity of the wave, generally measured in decibels (dB), and the pitch describes the frequency of the wave, measured in Hz.

For noise reduction, it is to prevent some sounds that we do not want to hear from entering the ear. The noise reduction mode mentioned in the question actually refers to the active noise reduction as we are familiar with. When it comes to active noise reduction, there is of course passive noise reduction. In comparison, let's talk about the relatively simple passive noise reduction.

Passive noise reduction (passive noise cancellation,PNC) is actually a relatively vague term, we can simply and accurately call it sound insulation, because this technology uses the natural shape and material of headphones to isolate ambient noise. PNC does not have any powered microphones or built-in technology to actively find and eliminate ambient frequencies. Around you and me, anything that can physically cover your ears can isolate noise. Is it "passive" enough?

This is not the case with active noise reduction (Active noise control,ANC), which gets its name from their built-in technology that actively looks for and eliminates ambient sounds before they reach the ear. These headphones have miniature microphones in each earmuff to monitor the ambient noise frequency from outside the earmuff and then generate a completely opposite sound frequency, which we call the antagonistic frequency (inverted). When the two sound waves meet, they produce a single, flatter sound, which our ears think of as a quieter sound (that is, the original noise is effectively eliminated). Being active means that the headphones are equipped with batteries designed to power these noise reduction microphones.

Active noise reduction icon | Image source [1] and as mentioned in the title, when we turn on the noise reduction function of headphones without music, we may notice that voices are still coming nearby, and sometimes it seems that the sound has been amplified. Why is that?

In fact, it is very simple. At present, most active noise reduction technologies are most suitable for frequencies below 500Hz, and there is almost no noise reduction effect for sounds exceeding about 1000Hz. Precisely, the most important bands of human speech articulation are 500Hz, 1000Hz, 2000Hz and 4000 Hz. However, most of the noise generated by some common vehicles, such as vehicle engines, is lower than 500Hz, so it can be greatly reduced or even completely eliminated by ANC. In addition, the frequency of human voice is generally unpredictable and changes too frequently, so the current ANC system is really difficult to deal with these sounds, which leads to the illusion that the human voice is "amplified".

See if this wave is what you say it is. [3] to sum up, PNC can better reduce medium and high frequency noise, while ANC is good at reducing low frequency noise. If you want to achieve the goal of isolating people's voices at the same time, try playing white noise in your headphones. Finally, of course, there are no earplugs or headphones that can block all sounds.

Reference:

[1] Noise-cancelling headphones

[2] FACTS ABOUT SPEECH INTELLIGIBILITY

[3] Why do I hear sound with noise-cancelling on?

By Gyoku

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop), author: Frions

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