On March 23, Shenzhou 13 astronauts Zhai Zhigang, Wang Yaping, and Ye Guangfu conducted a "dialogue between heaven and earth" at a distance of 400 kilometers at the China Space Station, and taught the second lesson of the "Tiangong Classroom" at the China Space Station.
This time, the "Space Teacher" mainly demonstrated the space "ice and snow" experiment, the liquid bridge demonstration experiment, the water and oil separation experiment, the space parabolic experiment, and introduced and displayed space science facilities.
Water polo becomes "ice hockey"
Wang Yaping "turned water into ice" to become magic
At the first "Tiangong Classroom", Wang Yaping used the solid water ring to make a water film and water ball, and carried out a series of experiments. In the second class, Wang Yaping did not use other utensils, took out the water bag and directly squeezed gently, the liquid crystallized at the mouth of the tube, after treatment, Wang Yaping squeezed out the liquid again, and the liquid ball quietly hovered in the space station cabin.
Next, a wonderful phenomenon appeared, after Wang Yaping touched the liquid ball with a small stick dipped in powder, it began to "freeze"!
In fact, the composition of the "water ball" made by Wang Yaping is a supersaturated sodium acetate solution. The saturated sodium acetate solution is heated, it has the ability to continue to dissolve more solutes, and then the solution after "feeding" is cooled, and the supersaturated sodium acetate solution is obtained. At this time, if no new solute is added, it will remain in a stable solution state in the water bag, safely survive the shock of the spacecraft launch, and successfully reach the Chinese space station.
But the solution is not as calm as it seems on the surface, just add a little more anhydrous sodium acetate powder, the "water ball" will begin to crystallize from the place where the powder touches, and the heat will be released during the crystallization process. Therefore, this "ice hockey" is actually a "hot ball"!
If this experiment is performed on the ground, the supersaturated solution is limited by the container and can only crystallize inward. The space station has a microgravity environment, and the solution does not need to be containerized to form a solution ball in the air, thus observing the change of material properties that are not affected by the earth's gravity.
In the space station
Build a "bridge" with water
In the first "Tiangong Classroom", Wang Yaping made a beautiful water film and placed a paper flower made with his daughter on the water film. Under the action of the surface tension of the water, the paper flowers slowly bloom along the surface of the water film, achieving a warm and classic scene.
This time, the same is to show the surface tension of the water to the children, Wang Yaping held two plastic plates, Ye Guangfu squeezed water on the surface of the plastic plate, the two plastic plates gradually approached, the water was connected to a "bridge" between the plates, Wang Yaping pulled the distance of the plastic plates farther, and the "bridge" was not broken. This is the "liquid bridge phenomenon".
In fact, in the ground environment, liquid bridges are not uncommon. When washing your hands, close two wet fingers, and then slowly separate a short distance, a small liquid column will appear between the fingers, which is the liquid bridge. However, due to the weak surface tension of the liquid, the size of the liquid bridge is usually difficult to exceed a few millimeters in a normal gravity environment. In the microgravity environment of the space station, the surface tension can "show great magic" and can maintain the large size of the liquid bridge without collapsing.
Ice pier unveiled in "Tiangong Classroom"
"Fly" out in a straight line
The mascot of the Beijing Winter Olympics, "Ice Pier", also appeared in the space classroom and became a "teaching assistant". Wang Yaping threw the cute "ice pier" mascot, which did not fall like on the ground, but "flew" out along a straight line.
This is the most intuitive embodiment of the microgravity environment of the space station, but why should such a simple experiment be brought to the "Tiangong Classroom"? Zhang Jian, the main classroom teacher of Tiangong Classroom and a physics teacher at the Second Affiliated Middle School of Beijing Normal University, explained that simple flat throwing motion was magnified to the cosmic scale in the mind of the famous scientist Newton. Since the faster it throws an object on the ground, the farther it can fall, can it become a satellite around the Earth if the speed of throwing the object is large enough?
This thought experiment is also known as "Newton's alpine cannon experiment", and the concepts of the first cosmic speed introduced by it have become an important basis for launching artificial satellites and space stations.
Such thought experiments are not uncommon in the history of scientific development, Galileo helped people understand the relationship between force and motion through ideal oblique face-to-face experiments, and Einstein proposed a strong equivalence principle with an ideal elevator in general relativity... Thought experiments based on logical laws and factual bases have played an important role in scientific progress.
On the space station
Water and oil do not naturally layer
In the classroom, in the vial in Wang Yaping's hand, it contained two substances: water and oil. In the space station environment, crystal clear oil droplets do not float on the ground, but mix with water, which echoes the phenomenon of bubbles churning in effervescent sheets in water during the first space lesson.
However, after Ye Guangfu tied the bottle with a rope and quickly rotated the vial, the water and oil were layered due to the centrifugal force. The principle behind them is the disappearance of density stratification in a microgravity environment, which is the most intuitive application of a microgravity environment.
Why call the station's weightless environment "microgravity"? In fact, although the space station has a weightless environment, it is not detached from the gravitational pull of the earth. In orbit about 400 kilometers from Earth, the space station is subjected to about 88.5% of the gravity of the ground, and is not significantly smaller than the ground. The reason why the space station can form a microgravity environment is because it has a very high flight speed, at this time, gravity becomes the right centripetal force, allowing the space station to orbit the Earth. But the Earth is not a uniform sphere, and the space station is not a constant speed, so the environment inside the space station is "microgravity" rather than "zero gravity".
Answering
Tears are shed in space, and tears swirl in the eye sockets
Some netizens asked the Shenzhou 13 astronaut crew: What are the tears in the space station, will they be stretched like jelly for a long time? In the exchange session of the "Tiangong Classroom", Wang Yaping responded that during the flight of the space station, they experienced many excited and tearful moments, at which time, the tears could not flow like on the ground, but would swirl in the eye sockets or stay in the corners of the eyes.
On the space station, astronauts also use Beijing time to schedule work and rest
In response to the question of "how to arrange the schedule of astronauts"? Zhai Zhigang said that on the space station, astronauts have to experience sunrise and sunset every 90 minutes. In the space station, there are both Beijing time and world time, as well as relative flight time and absolute flight time. Depending on the task, the time standard used varies. In the case of manned presence, the beijing time arrangement of astronauts' schedule is generally adopted.
Wang Yaping said that the skin condition is very good
Some netizens asked: Will the skin get better in space? Wang Yaping explained that the space station has no sunlight, the temperature and humidity are also controlled within the appropriate range, and in the microgravity environment, the body fluids will be distributed upwards, and the skin will also be lifted upwards, so I feel that the skin state in the space station is very good. In addition, on the space station, skin care water and the like can not be poured out, and must be squeezed with a specific device.
Beijing Daily (ID: Beijing_Daily) reporter Liu Suya, @ CCTV News [Please indicate the source of reprint: Beijing Daily WeChat public account]
![Vivid and fun! The second space lecture of the Chinese space station was successfully completed[fig]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)