Editor's Note
At the beginning of the New Year in 2022, the curtain was officially opened on the exhibition of outstanding works of the Chinese Physical Society. There is nothing better suited to greet the first touch of green, the first rays of light, the first breeze of spring than the vibrant spread of science. We hope to stimulate young people's endless curiosity about the world, have scientific dreams, set great ambitions, and start from here on an interesting journey of exploration.
The Chinese Physical Society, with the mission of guiding the public to attach importance to science, respect science and develop science, has established a science popularization working committee since 1982, which is committed to popularizing scientific knowledge, disseminating scientific ideas and promoting the spirit of science. In order to encourage the production of more outstanding original science popularization works, the Science Popularization Working Committee of the Chinese Physical Society organized the "Physics Science Popularization Works Exhibition" activity in 2021 to collect original popular science works videos for physics researchers, teachers and students. The content of the works includes two categories: (1) three minutes of wonderful science - short videos explaining physical knowledge, physical thinking methods, the content mainly revolves around the teaching content of physics in colleges and middle schools or physical phenomena in daily life; (2) the inventors on the podium - self-made physics science teaching aids, exhibition tools, etc. Video display. After the preliminary evaluation and re-evaluation of the expert jury, 59 excellent works were finally selected. As one of the series of activities to celebrate the 90th anniversary of the founding of the Chinese Physical Society, we have selected 5 more from these 59 works and exhibited them on the occasion of the Spring Festival to welcome another spring of science.
On the occasion of the Spring Festival, the Chinese Physical Society congratulates physicists across the country and all those who love physics with good luck and a happy Year of the Tiger!
01
The secret of the hand-touch battery
Electricity lights up thousands of homes, but have you ever thought that our human body can also become part of the "great closed loop of electricity"? Because we have a large number of ions in the human body, just as the water droplets in the water pipe can be collected to produce water flow, they will produce an electric current after the directional movement, which is the principle of human conduction. Conduction is an important part of human life activities, as early as 1791, the Italian medical and zoologist Luigi Galvani found that the muscle movement of living things is closely related to the current that passes through, and our physiological phenomena such as neural activity are achieved through the "microcurrent" inside the human body. And when there is an external current through our human body, once the current is too large, the energy carried by the current will be harmful to the human body like a flood, which is the reason for our electric shock, "poison oath by lightning" and other sayings are actually related to human conduction.
In this process, ions also have to overcome the resistance of crossing the "mountains" to generate current, which is also called resistance. The resistance of the human body is also changing at any time, the human body sweat, body temperature increase, etc. can reduce the resistance, and we can also manually increase the resistance to "block" the current. One of the secrets of power workers working on high-voltage power grids that they are not electrocuted is to wear insulating gloves, which have huge resistance and thus firmly hinder the flow of powerful currents through the workers' bodies.
In recent years, cases of deceiving the elderly under the guise of medical devices have emerged in an endless stream, and the "health detector" mentioned in the video is a false device that uses the indication of the galvanometer as a "health indication". The sound of the liar hits the west, the surface seems to be a pill to play a role, in fact, the hot water taken makes the human body sweat slightly, and the sweat on the hand after sweating can reduce the resistance of the human body, so it seems that the human body current has increased significantly. When the Spring Festival comes, it is often also a good time for scammers to "rush performance" in the year. The learning of scientific knowledge by the whole people is not only an important part of improving the scientific literacy of citizens, but also an important "protective umbrella" for each of us to prevent fraud.
02
The secret of the gravitational slingshot
"Use gravity to catapult the big bow of gravity!"
- Gravitational slingshot effect
Galileo
In everyday life, gravity is so common that it is almost impossible to notice, but if we go deep into the vast universe, we will find that gravity is the ultimate boss! We know that there are four basic interactions in the universe, gravity is one of them, and in terms of influencing the motion of celestial bodies, the influence of these four forces, gravity is almost dominant, so when we explore outer space, whether we can use gravity has become one of the questions of great interest to scientists, and one of the most well-known and common applications is the slingshot effect of gravity.
The slingshot effect of gravity is a very figurative metaphor that describes a phenomenon in which a tiny object and a very large object are chasing each other close, and the gravitational pull between the two objects will cause the large object to transfer a part of its energy to the small object and throw the small object out like a slingshot ejection.
The ideal experiment in the video is very instructive, and we may be familiar with a very intuitive description of general relativity, which uses objects on a rubber film to make the membrane dent to simulate the curvature of space-time, and we must have heard that Newtonian gravity can be seen as some kind of approximation of general relativity. But using this demonstration of the curvature of space-time to explain the interesting effects of gravity is an interesting attempt by the ideal experiment in this video. This experiment tells us very intuitively that the gravitational slingshot effect did speed up the small object and eject it!
This phenomenon has a very clever application when humans explore outer space, humans want to launch spacecraft into outer space, but the gravitational pull away from the sun consumes a huge amount of fuel, but scientists realize that using this phenomenon can make clever: if I can't carry so much fuel, I will use the huge stars in the universe to eject the spacecraft. Human journeys to the distant universe, such as the launch of cassini, Galileo, and Voyager spacecraft, have been repeatedly used by humans to use the major planets of the solar system as slingshots to relay them out.
03
Correction of myopia
In the documentary, have you ever seen a shot of a magnifying glass igniting? (Play with fire hazards, don't imitate!) A magnifying glass is essentially a convex lens that is able to refract light rays so that they come together. The more curved the surface of the convex lens, the stronger the ability to concentrate light. Conversely, concave lenses can cause light to diverge.
At the front of our eyeball, there is a structure called the lens, which acts like a convex lens, bringing together the light entering the eye from the outside, and this converged light will focus on imaging on our retina, and the brain can see the object for further processing of imaging. When the distance from the lens to the retina is constant, when we look at a near object, because the light entering the eye is from a point and is not parallel, it often requires greater curvature; while the light entering the eye of a distant object is nearly parallel, so only a small curvature is needed to make us see clearly.
And how do our eyes do things that are far or near enough to allow us to see clearly? There is a layer of muscle on the periphery of the lens called the ciliary muscle, and normally, the ciliary muscle can adjust the curvature of the lens by controlling its own tension and relaxation, so we can always see the object very clearly. However, for today's humans who stare at near objects such as screens and mobile phones for a long time, in order to make the lens curvature larger, long-term in a state of tension, this state will weaken the recovery ability of the ciliary muscle, so when we look at distant objects, the lens will overly converge light, so that imaging in front of the retina, resulting in unclear vision, this is myopia phenomenon. In order to correct myopia, myopic patients need to wear a concave lens, slightly divergent into the eye of the light, so that just on the retina, the larger the curvature of the lens, the stronger the need for the concave lens divergence ability, the smaller the focal length, so this is what we often say the higher the degree.
If the imaging is at the back end of the retina, this is farsightedness. In the same way, for patients with farsightedness, a convex lens is required to converge the beam in advance for correction. For older people, their ciliary muscles are in a long-term relaxed state, so the control of the lens is poor, the lens arc is small, so it is easy to produce hyperopia, which is why farsightedness is often called "presbyopia".
In addition, when wearing myopic glasses, we often hear the problem of "astigmatism", so what is the relationship between astigmatism and myopia? For astigmatism patients, the lens is not a perfect convex lens, the focal length of the center of the lens in different directions is different, which means that the light incident in different places will be imaged at different distances before and after the retina, and the light is as if it is scattered, so it is called astigmatism.
In fact, myopia is essentially equivalent to the long-term work of the eyes, in a state of excessive tension, so in addition to learning to work, you may wish to go out and let our eyes relax and relax.
04
The secret of dry ice
"Dry ice
Many high-end restaurants will increase the smoke-filled "white fog" effect when the dishes are presented, and the production of this "white fog" is closely related to the use of dry ice. Dry ice is not ice, in fact, dry ice is solid carbon dioxide, because carbon dioxide exists in the form of gas at room temperature and pressure, so dry ice will be directly converted into carbon dioxide gas at room temperature, this process of converting from solid to gaseous state before being solid is called sublimation. Sublimation phenomenon is very common around everyone, and the mothballs placed in the wardrobe will gradually become smaller, which is also the process of sublimation.
Why don't we usually see dry ice converted to liquid, but instead sublimate it directly? Because the presence of three states of matter (solid, liquid, gaseous) requires a specific temperature and pressure range. The presence of liquid carbon dioxide requires at least 527 kPa (about 5 atmospheres), so liquid carbon dioxide is not present at atmospheric pressure. In fact, the manufacturing process of dry ice is not frozen to low temperatures, but is made by adding carbon dioxide gas.
Sublimation, the process of transforming from solid to gaseous, absorbs a lot of heat, so the "fruit smoothie" in the video takes advantage of this principle. When we buy frozen food on the Internet, we often use dry ice as a refrigerant in the package (different from brine ice packs, which disappear due to sublimation contents when left at room temperature for a period of time). The "white mist" mentioned at the beginning of the dry ice into the water to produce "white fog" is the use of this principle, but the "white fog" is not the carbon dioxide gas produced by the sublimation of dry ice, because the carbon dioxide gas is colorless and odorless, and we cannot see it with the naked eye. The "white mist" is actually a small droplet of water that absorbs heat when dry ice is sublimated, causing the water vapor in the air to condense into small droplets. Because the density of carbon dioxide is greater than that of air, the effect of "white fog" produced by dry ice entering the water is often gathered in the lower part of the space, like a flowing cloud, so it is often used for stage and film and television drama shooting, creating a "cloud wonderland" effect. Like dry ice, many seemingly uncommon substances are already widely used in our lives!
05
The secret of the hot piano
Wind music is a type of instrument that is widely present in the world, such as Chinese gourd silk, Western saxophone, Australian Aboriginal digiridu pipe, etc., this type of instrument has a pipe of greater or smaller size as the main body, the material may be bamboo, metal, wood and so on. Different materials and lengths give them different tones and timbres, but the principles by which these instruments sound very similar.
Sound is produced due to the compression of the object, and in daily life, the compressed object is naturally air, the sound source makes the air compressed at a certain frequency, resulting in dense alternating air waves, which are transmitted to our ears and will cause the eardrums in the ear to vibrate, and then be processed into sound signals by our brains. The long pipes of the wind music are the secret of their sound, when playing, we will produce a small air vibration at the end of the instrument, this vibration will make the air column inside the pipe vibrate, and the vibration of the air column will rub against the inner wall of the pipe, which will trigger a greater resonance of the pipe body, so the tiny sound will be amplified. The tiny vibrations we induce when playing instruments are in many ways, such as the saxophone vibrating the whistle, and the trumpet directly using the lips to vibrate.
Is there another way to induce sound generation? The thermosonic effect mentioned in the video is a new way. After the air is heated, the temperature will increase, so that the density of the air will decrease. When the heat source is located in the lower part of the tube, the hot air with less density below will rise, and the cold air with the higher density will sink, and the convection of this air will cause the air to oscillate periodically, so that it can make a sound. Since this density-taking advantage of convection can only occur up and down, no sound is produced when the tube is placed across the video.
At present, there are relevant studies in China that use the thermoacoustic effect to use emerging materials such as graphene or carbon nanotubes as heat transfer substances to create a new type of speaker. Maybe one day in the future, we can buy speakers and headphones based on the principle of thermoacoustic effect, because it is not a sound generated by membrane vibration, so there is no need to worry about the problem that the membrane will break after puncturing, but the biggest drawback may be that the ears are hot.
Contributed by: Yearly
Typography: Big Cute / YouHeng
Editor: Farmer
Editor-in-Charge: Rational
Source: Chinese Physical Society
Edit: Aloysius