Source: Global Times - Global Network
On December 9, the first space lecture in the Stage of the Chinese Space Station was conducted simultaneously in the main classroom of the China Space Station and the Ground Main Classroom in the China Science and Technology Museum, as well as the ground sub-classrooms in Nanning, Sichuan, Hong Kong and Macao in the form of interaction between heaven and earth. Three astronauts in the Shenzhou 13 crew, Zhai Zhigang, Wang Yaping and Ye Guangfu, demonstrated cytological experiments, human movements, liquid surface tension and other phenomena in the weightless environment, and carried out a total of 8 space teaching projects.
Why did these programs be chosen as the teaching content for the first time of Tiangong Classroom? What knowledge points are behind each experiment? The Global Times reporter interviewed the science popularization experts who participated in the "lesson preparation" process of the space lecture.
Space Turn Knowledge Point: Angular Momentum
In the space lecture held on the 9th, the three astronauts first showed the magical phenomenon of turning around in space. This ordinary action, which originally had a zero difficulty coefficient on the ground, hides a high degree of physical knowledge in space.
Chen Zheng, deputy head of the Science Popularization Lecturer Group of the China Science and Technology Museum, told the Global Times reporter that the core keyword of the space turn experiment is called angular momentum. Angular momentum is a physical quantity that describes the rotation of an object. What this test shows is that in a microgravity environment, the astronauts in the case of not touching the space station, similar to the ideal state to verify that "there is no external moment, the object will be in the conservation of angular momentum." When the astronaut's upper body is rotated to the left, according to the principle of angular momentum balance, the lower body will turn to the right.
Another action is when the astronaut stretches his body, because the mass distribution is farther away from the axis of rotation, the rotation inertia is relatively large, so the angular velocity is slowed down, in layman's terms, it is slower. When the limbs are withdrawn, the rotation inertia is small, the angular velocity will increase, and the intuitive feeling is that the rotation speed becomes faster.
Buoyancy disappearance experiment Knowledge point: Buoyancy and gravity are associated
In many science fiction movies, there have been scenes where once gravity is gone, buoyancy is gone, and people have a harder time swimming. The buoyancy disappearance experiment carried out by space teacher Wang Yaping shows this phenomenon.
Chen Zheng told the Global Times reporter that the experiment shows the phenomenon of buoyancy and gravity. Buoyancy arises from the difference in pressure of the liquid at different depths caused by gravity. When gravity disappears, the internal pressure of the liquid is the same, and the buoyancy is also gone. However, it is difficult for the buoyancy on the surface of the earth to disappear, and this experiment is difficult to visualize intuitively. Under the microgravity conditions of the space station, the associated relationship between buoyancy and gravity can be very clearly visualized.
Water Balloon Optical Experiment Knowledge Point: Convex Lens Imaging Principle
The space water balloon optical experiment demonstrated by astronaut Ye Guangfu showed three physical principles at the same time.
Chen Zheng said that when the astronauts punched a bubble into the water balloon, because the buoyancy in space has disappeared, so the bubble will not float upwards, but honestly stay in the water balloon, the water balloon is thus turned into two parts by the bubble, the middle is air, and the bubble is surrounded by water. At this time, the whole water balloon becomes two lenses, the outer ring becomes a convex lens, so it presents an inverted image, the inner ring is equivalent to a combination of two concave lenses, and at this time there is another upright image. Therefore, you can see two images of one positive and one upside down at the same time in the water balloon.
This experiment actually reflects three physical phenomena, the first is that in the weightless environment, the water droplets will shrink into a water ball close to the perfect sphere under the action of surface tension, and on the ground, because of the influence of gravity, the water droplets appear as water droplets, and it is almost impossible to obtain a perfect water ball. Second, the water balloon can be seen as a convex lens, and if you stand outside the twice the focal length of the convex lens, you see an inverted real image. Finally, it is to punch a bubble in the water ball, because the buoyancy in space disappears, the bubble will not float out, it will honestly stay inside.
This experiment can actually be simulated through glass on the ground, but it is certainly not as good as the effect of water balloons.
Effervescent tablet experiment Knowledge point: microgravity environment
The effervescent film experiment conducted by the astronauts is an interesting experiment in this space lecture.
Chen Zheng introduced that in the ground environment, the effervescent piece thrown into the water balloon, you can see the bubble floating, but in the weightless environment of the Chinese space station, because of the disappearance of buoyancy, the bubbles produced by the effervescent piece thrown into the water are no longer floating, but squeeze each other, and finally form a very interesting look, this water balloon will also be held up by the bubble more large, you can see the effect of the water balloon expanding a little.
Because the biggest difference between the space station and the ground is that the space station is a microgravity environment, but the microgravity environment is only a noun for ordinary people, through these experiments, we can know that in the microgravity environment, many physical phenomena are different from the ground environment.
Chen Zheng said that the reason why these physical experiments were selected for space teaching this time is based on many considerations, first of all, from the perspective of safety, the experiments carried out by space teaching must be carried out under the condition of ensuring the normal operation of the Chinese space station, because the Chinese space station is a brand new space station, and astronauts have a lot of work to do. So the experiment of teaching space must first ensure safety, which is the overriding criterion.
Secondly, from the perspective of teaching, there is a clear difference between the sky and the ground, so it is necessary to choose some experimental projects that can see the obvious difference between heaven and earth, so that everyone can intuitively feel the difference between the space environment and the ground environment of the space station
Finally, it is hoped that the experimental content and process of space teaching will not cause an excessive burden on astronauts. Because the astronauts' work on the space station is very busy, the workload is very large, the content of space teaching, the operation should not be too complicated, should be as simple as possible, can quickly show the effect, can not consume too long time, and can not increase the pressure of astronauts' work.
After the space lecture, whether the content taught by the three astronauts is expected to become a major test point for future examinations has also aroused many reverie. In this regard, Chen Zheng said that he did not want to carry out such an extension. The space teaching content of the astronauts is an inspiration for the children, that is, they hope to use the experimental way and the way of interaction between heaven and earth to stimulate the children's curiosity and play a leading role, which is also a very important role in this space teaching.
"It's not just about indoctrinating knowledge, but after reading the content of these experiments, you can let the children explore what else to do, and let the children try more possible solutions on the ground." Let the children understand the deeper things behind this. Tiangong Classroom is a main classroom, there are thousands of sub-classrooms on the ground, these sub-classrooms can also extend these contents, it will achieve a very interesting effect, I especially like such a form. Chen Zheng said.