The "online class ceiling" is updated again!
At about 15:40 on March 23, 2022, our "space trip trio" brought the second lesson of Tiangong to earthlings!
Source: CCTV News
What the? What the? I heard that on the Chinese space station:
“
Teacher Wang Yaping made an "ice hockey"?
Top-notch ice piers in space?
Can you build a bridge with liquids in space?
And Heaven and Earth Interactive?
”
Move the small bench, the focus is on ~
Space "ice and snow" experiments
What happens to the crystallization of saturated liquids in weightlessness?
On the ground, the use of saturated liquid crystallization is a method of separating and purifying solid substances.
Source: China Digital Science and Technology Museum, Science Popularization China
Supersaturated solution refers to a solution with a concentration exceeding the theoretical equilibrium concentration, and the excess solute will precipitate crystallization, and a solid substance of higher purity can be extracted through filtration, washing, drying and other steps.
A supersaturated solution is an unstable state that is prone to crystallization when disturbed by external factors. Crystallization is affected by many factors, such as temperature, pressure, shear force, ultrasound, external magnetic field, etc. The crystallization process is the first formation of the crystal nucleus under the influence of external factors, and the crystal nucleus gradually grows to complete the crystallization process.
In the Tiangong classroom, teacher Wang Yaping in the process of squeezing the saturated solution twice, the crystallization phenomenon at the nozzle of the tube also explained the instability of the supersaturated solution, and the pressure brought by the squeeze induced crystallization.
Under weightless conditions, sodium acetate solution can detach from the container to become a stable liquid ball. Teacher Wang Yaping induced sodium acetate to quickly complete crystallization by dipping the crystal nucleus into the supersaturated liquid ball. Crystallization is an exothermic process, so the ice hockey is hot to the touch.
Crystallization experiments with supersaturated solutions can only be performed in containers on the ground, and the ice crystals generated during crystallization are the same shape as the container and cannot become ice balls like space.
Liquid bridge demonstration experiment
Is the surface tension of water still there in a weightless environment?
A liquid bridge is a small column of liquid between two solids.
Liquid surface tension is a force that acts on the surface of a liquid to reduce the surface area of a liquid. Liquids have surface tension, especially under the action of weightlessness, the surface tension will be more "mighty".
The surface tension makes the surface of the liquid equivalent to the existence of something similar to an "elastic film", which binds the movement of the liquid. Its essence is that there is a thin layer on the surface of the liquid in contact with the gas, called the surface layer, the molecules in the surface layer are sparser than the inside of the liquid, the distance between the molecules is larger than that inside the liquid, and the interaction between the molecules is manifested as gravity. For example, when the spring is pulled open, the spring shows a tendency to shrink.
Under the action of ground gravity, due to the weak surface tension, the size of the liquid bridge formed in the normal gravity environment is very small (usually only a few millimeters), beyond which the liquid bridge will not be able to balance its gravity and collapse.
In space, due to weightlessness, a liquid bridge with a large diameter can be formed, and a liquid bridge with a diameter of 50 mm has been built on the ISS (International Space Station).
Liquid bridge between fingers, image source:
http://www.csu.cas.cn/kxcb/kpdt/201609/t20160907_4659506.html
Although the size of the liquid bridge on the ground is small, it cannot be underestimated! On closer inspection, there are many examples of liquid bridges in life:
On the beach, the dry sand can be pinched into various shapes after mixing with water; (this is due to the fact that the water forms a liquid bridge between the fine sand particles, so that the sand can be gathered together)
On the smooth tabletop, the white paper dipped in water is glued, also because of the liquid bridge formed between the paper and the desktop;
……
Water-oil separation experiments
Will water and oil delamination disappear in weightless environments?
On the ground, water and oil are layered, always water below and oil on top. This is due to the fact that water and oil are not miscible, and the density of oil is lower than that of water, so it floats on top of water.
But in the space station, because there is almost no gravitational influence, the density of the large no longer sinks, the density of the small is no longer floating, water and oil mixed together, can not see the boundary between the two. By rotating, the layering of water and oil can be achieved.
So why is that?
In the case of the same volume, the density of water is greater than that of oil, and the mass of water is greater. According to the centripetal force formula F = mrw2, when the angular velocity w and radius r are the same, the mass m is large, and the larger the centripetal force required by the water droplet, that is, the greater the equivalent centrifugal force, so the larger mass of water is thrown to the bottom of the bottle. Water and oil are layered.
Space parabolic experiments
What is the difference between the trajectory of the heavenly and underground projectiles?
Throwing an object on the ground, due to the gravitational force that has been subjected to vertical downwards, analyze its trajectory to see the speed of the thrown in what direction:
When the throwing speed is in the vertical direction, whether it is thrown up or down, it is a linear variable speed movement;
When the speed of the thrown object is no longer in the vertical direction, whether it is thrown obliquely or horizontally, the object movement is a curved variable speed movement.
In space, because in the space station module, the object is almost not affected by gravity, no matter which direction it is thrown, it can almost be seen as a uniform linear motion, because the object is only subject to weak air resistance, and the change in speed direction and size is very small.
Therefore, in the space station module, the projectile should be alert, the astronaut should be transformed into "Harry Potter", and the grasp of the flying object should be stable and accurate, in order to prevent the object from touching other instruments and equipment.
Some people say that the space station is very close to the earth, about 400 kilometers, if calculated according to g = GM/ r2, the gravitational acceleration is about 0.9 or so on the ground, the gravitational acceleration is so large, why is it microgravity?
The principle of microgravity on the space station, source: http://www.cmse.gov.cn/xwzx/zhxw/202203/t20220315_49392.html
This is because the space station moves around the earth, there will be centrifugal force, and the gravity it is subjected to is exactly offset by the centrifugal force, so all the objects in the cabin will not be affected by gravity and will float.
Source: Popular Science China