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

I wonder if you have a dream that you will continue to grow taller. In physics, there are also some special ways to support us to expand Q1. Why do you have to add cold water to cook dumplings three times? By Anonymous

A:

Earlier cooking dumplings with cold water is probably because the previous firepower control is not as casual as it is now, the water is too fast, and many times the dumplings are cooked, but the stuffing is not ripe. After all, the thin skin and big stuffing has always been a good accomplishment of excellent dumplings. But the dumplings have been boiling in the boiling water, it is easy to boil the skin, it is really turned into a piece of soup balls. So add cold water to reduce the water temperature to ensure that the stuffing will be cooked without breaking the skin, and the cold soup will stop boiling.

As for now, it is very easy for us to use the gas stove to control the firepower. If you don't want to add cold water, you can cook it slowly with minimum firepower. Of course, you can also cook it.

However, regular readers may know that we answered in No.316 Q2 that cooked noodles with cold water will be stronger and less prone to adhesion, probably because it inhibits the gelatinization of starch, increases the crystallization area of starch grains, and enhances the mechanical properties of the dough. In fact, dumpling skin is the same, dumpling skin with cold water is often more resilient, it is not easy to break the skin, and tastes better.

By Frost White

Q2. Why do you feel that your voice on your mobile phone is different from that in reality? by.

A:

Different modes of transmission lead to different timbre. Listening to the speech on the mobile phone is air conduction, while listening to your own speech depends on both air conduction and bone conduction.

First, air conduction, the air vibration caused by external sound, is collected through the auricle, and the resonance of the external auditory canal is amplified to force the tympanic membrane to vibrate. The vibration enters the inner ear through the auditory ossicles, stimulates the cochlea, and the cochlea converts mechanical vibration signals into nerve signals. Through the auditory nerve to the auditory center of the cerebral cortex, we hear the sound.

The conduction path of bone conduction is much simpler. When people make sound, the vibration of the vocal cords will directly drive the vibration of the skull, and the vibration of the skull will be directly transmitted to the bone labyrinth, driving the internal and external lymphoid vibration of the inner ear, stimulating the spiral apparatus, and converting the vibration into nerve impulses, which are transmitted to the auditory center of the cerebral cortex through the auditory nerve.

The main pathways of air conduction and bone conduction

The timbre of the two modes of transmission is different. The sound we hear is composed of a pitch and many overtones. These overtones determine the different timbre, and the overtone is closely related to the vibration medium. For example, the faster the harmonic decays, the softer the sound, and the slower the attenuation, the harder it is.

Therefore, the difference between the two conduction media will bring slight differences in timbre, and we naturally sound different, which is a very normal phenomenon.

It is also important to note that the sound heard while listening to the recording may also be distorted to a certain extent due to factors such as recording equipment, playback equipment, and audio sampling and processing methods, but we should also be able to feel that the difference between listening to other people's recording and listening directly to others is far less obvious than listening to your own.

By Frost White

Q3. What is the principle of throwing guns in the New year? By Gollum

A:

Before we answer the principle, let's take a look at the structure of the gun drop (I'm sure you've removed the dog's head, too).

The outside is a beautiful outer package, inside is a lot of pebbles and some powder, the key lies in this powder.

There are probably two types of guns we can buy at present: the first powder is KClO chlorate, red phosphorus, and the second powder is silver fulminate (Ag C, N O). Take the powder of potassium chlorate and red phosphorus as an example: potassium chlorate is a strong oxidizer and phosphorus is a strong reducing agent. when we throw the cannon on the ground quickly, potassium chlorate reacts with each other to produce oxygen when the pebbles friction each other.

When heated, the oxygen produced will burn with phosphorus and produce an explosive reaction. Among them, the pebbles in the gun drop rub against each other to a certain extent, which determines the intensity of the chemical reaction, that is, the "loudness" of the gun drop. Master a certain skill (drop hard) your gun drop will be louder than others. Finally, an additional answer. Silver in silver thunderate can be extracted by chemical reaction, that is to say, every time you drop the gun, it may really be silver in white flowers.

Tips: be sure to pay attention to safety when setting off fireworks!

By justiu

Q4. Why is there a welcome text message as soon as you enter a prefecture-level city? How did they locate me? by Anonymous

A:

This is the positioning through the mobile phone base station, the specific principle, please listen to the editor.

The base station is a kind of radio station that transmits information with mobile terminals (mobile phones, etc.). When we use a mobile phone to make a call, the mobile phone will send the modulated signal to the nearby base station An in the form of electromagnetic waves, and the base station A will send the signal to the base station B near the other party, and the base station B will send the signal to the other party's mobile phone. the specific principle is shown in the figure.

Image source: because the intensity of the electromagnetic wave in the network attenuates with the increase of distance, the control range of the base station is limited in order to ensure the strength of the signal. In the 2G era, a base station is usually responsible for signal transmission in the surrounding 10km. In the 5G era, the shortwave diffraction ability used by the base station is not strong, so a single base station is usually only responsible for signal transmission in the 100m-300m. In order to ensure that the signal range of the base station is as wide as possible and does not overlap with each other, the base station is usually arranged in hexagons, which is similar to the cellular network.

The base station regularly broadcasts the information that belongs to the base station by radio. When our mobile phone enters the service range of a base station and receives the base station information, it will record it and determine whether it has entered the new base station. Every time you enter a new base station, the mobile phone will send a message to the corresponding base station to notify the identity information of the mobile phone. In this way, if the mobile network service of a prefecture-level city finds that your mobile phone sends a signal to the city's base station for the first time in a short period of time, it will control the corresponding base station to send you a welcome text message.

By single male youth

Q5. If the space elevator rotates with the earth in synchronous orbit, shouldn't the top satellite be thrown out when the rope breaks? why is there a scene of wandering the earth like that? By Anonymous

A:

Q: why is the space elevator falling in the movie?

A: such a plot has impact and appeal, vividly and intuitively shows the difficulties and setbacks encountered by human beings in the process of wandering the earth, and eulogizes the indomitable spirit and fearless character of human beings in saving their homes. Setting such a plot at the beginning of the film is fascinating, which not only sets the tone of tension and excitement for the film, but also lays the groundwork for the later contradictions and conflicts.

Of course it's just a joke. Let's take a look at whether the elevator should fall or fly out. The following picture is a schematic diagram of the space elevator in the wandering earth. In the setting, the whole elevator is stationary relative to the earth, and the orbital altitude of the space station is 38000km. In reality, the geosynchronous orbit is about 36000km. In the movie, people slow down the earth's rotation, so the height of the geosynchronous orbit is a little lower than the actual height.

The structure of the space elevator indicates that the steady-state space elevator should satisfy that the angular velocity is the same as the rotation speed of the earth, and the overall gravity provides centripetal force. Below the geosynchronous orbit, the gravity is greater than the required centripetal force, and the upper structure is required to provide an upward pulling force. Above the synchronous orbit, the gravity is less than the required centripetal force, and the lower structure is required to provide a downward pull-there is tension inside the elevator, and the whole elevator, like a straightened elastic rope, will fly out to both sides no matter where it breaks off. that is, the structure below the breakpoint will fall to the ground, and the structure above the breakpoint will be thrown off.

The scene of the elevator falling [2] in the movie, there doesn't seem to be a long cable attached to the space station when it falls, so it can be thought that the break point of the elevator is below the space station. According to this judgment, the space station should indeed be thrown away instead of falling.

Of course, these analyses are carried out under ideal conditions. We ignore the existence of the atmosphere, as well as the long process of "falling" and "flying"-China's first man-made earth satellite, Dongfanghong-1, has long lost power and slowed down slowly, but it has not fallen to the ground to this day.

Then again, the plot is just a science fiction movie, not a documentary or a screenshot of a physics lecture. Why on earth does the film appear to fall rather than fly? perhaps the initial high school Chinese reading comprehension is closer to the answer than the calculation and analysis below.

Reference:

[1] Space elevator signal

[2] the elevator fell.

By is a Tibetan fanatic.

Q6. What is the principle of the laser pen splitter? By is too external SC2106H

A:

In a word, the splitter in front of the laser pen is a cylindrical lens, which is used to radiate the laser in a straight line in the direction in which the cylindrical lens is bent.

Compared with the more common circular lens, the surface of the cylindrical lens is cylindrical, while the curved surface of the circular lens is spherical; the circular lens can deflect light in both dimensions, and the cylindrical lens deflects light only in the direction of curvature.

The light emitted by the laser diode chip in the laser pen will get a small light spot which is approximately circular after passing through the integral lens. If it diverges through a circular lens, it becomes a large circular spot, while if it passes through a cylindrical lens, it becomes an oval spot because it diverges in only one direction. (for "divergence", see Note [1])

Fig. 1 the laser pen with a splitter often appears in the physics class teaching refraction and reflection in junior high school after the light spot diverges through different kinds of lens. in order to show the light path of refraction and reflection, we will put a white screen on the back of the whole device. let the scattered laser leave a mark on the screen. This application scenario does not require high aberrations of cylindrical lenses, so colorless and transparent dielectric columns (such as a small section of glass rod) can also be used instead of flat-convex cylindrical lenses, which are more common in optical experiments.

Note [1]: generally speaking, we think that a convex lens (whether a circular lens or a cylindrical lens) has a converging effect on the beam, but when the distance between the observed position and the lens is to a certain extent, the observed spot is larger than the incident beam, that is, it is "divergent" from the result.

Fig. 2 "convergent" and "divergent" by optical slag

Q7. The universe is expanding. Is that person expanding? By Red Bean is a difficult country.

A:

In the last question and answer (No.343) Q8, the editor mentioned Hubble's Law:

It is used to describe two particles which are still in coordinates and whose physical distance is equal to each other. The velocity away from each other due to the expansion of the universe is proportional to the distance. The proportional coefficient is characterized by the Hubble constant H. So, you might as well take a 1.8-meter-tall classmate to do an experiment to see if the student is expanding.

Suppose the atom at the top of the tallest hair on the top of the student's head is particle 1, and the atom at the bottom of the toe used by this student to dig out the three rooms and one hall is particle 2, then the physical distance between them is recorded as

More recent measurements show that the Hubble constant is about [1], where ly is light-year. Bring in the above data, and since one light year is equal to 9460730472580800 meters, the speed at which the two particles farthest away from each other on the student's body are

In other words, every second this student will "expand" rice! According to a rough calculation, if this student wants to grow 1cm by relying on the expansion of the universe, he will have to wait for a second year, that is, more than 79 million years of 🤔.

But of course, even if this student really expands to a negligible degree, the editor can't expand 👻.

Reference materials:

[1] Hubble constant | Definition, Value, Units, & Facts | Britannica

By Callo

Q8. How do humans perceive four-dimensional space? By. Hey.

A:

It is difficult to feel the four-dimensional space intuitively, so let's start with the promotion of dimension. If zero dimension is a point, then the point motion becomes an one-dimensional line, the line motion becomes a two-dimensional surface, and the surface motion becomes a three-dimensional body. Now move the body in a direction perpendicular to the three-dimensional space, and the trajectory left is the four-dimensional space.

Now think of a specific shape in a four-dimensional space. If we upgrade the square in two-dimensional space to xyz three-dimensional, we will get a cube. What would it be like to add another dimension w? I don't know. No one has seen it with their own eyes. Let's call it tesseract for now. In order to express it as much as possible, we first add the fourth dimensional coordinates to the three-dimensional model of the cube.

Note that the above image is only showing a three-dimensional model in four-dimensional space with a two-dimensional screen. In fact, these four axes should be perpendicular to each other. Then, according to the reasonable extrapolation of the body moving into a superbody, move the cube along the w-axis.

The trail thus dragged consists of 16 points, 32 lines, 24 squares, and 8 cubes. Some bodies do not look so square because the picture shows the projection of a four-dimensional hypercube in three-dimensional space, which distorts the shape, just like the two-dimensional shadow of a cube is not necessarily a square.

Let's consider the rotation of the hypercube. In three-dimensional space, we can say "rotate the xy plane around the z axis", where z is the axis of rotation and xy is the plane of rotation. But in four-dimensional space, if we rotate the xy plane, neither the z-axis nor the w-axis perpendicular to it will move. At this point, the concept of axis of rotation is not easy to use, because the fixed part of the whole space is no longer a line, but the whole zw plane. In the image below, we highlight a cube in the hypercube to give you a sense of what its three-dimensional projection looks like when it rotates along the two rotating planes.

Finally, take a look at what a hypercube looks like when it passes through three-dimensional space.

With such strange changes, it is no wonder that Chu Yan can easily destroy water droplets through four-dimensional space in the "three-body".

Reference:

[1] Tesseract-Bartosz Ciechanowski

By sheep herding

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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