As we all know, water vapor condenses and condenses around condensation nuclei, which is the basis of cloud formation and rain. We call this condensation or condensed product cloud drops. The clouds we usually see are actually composed of thousands of cloud drops. From this perspective, there is not much difference between the clouds in the sky and the fog on the ground. In fact, the same is true when you fly closer. Cloud droplets are not all small water droplets. The cloud droplets in a cloud may be water droplets, ice crystals, or supercooled water droplets (that is, water droplets with a temperature lower than 0°C. Don’t ask me why it doesn’t freeze. Icing is not the only condition of temperature), and there may be two or three of them. A cloud drop floats in the air lifted by the updraft, just like a person blowing into a feather in the air to keep the feather floating in the air. But the cloud drop is not like a feather. Its quality is not static, but will continue to grow. There are two main ways for Yundi to grow, one is to further condense and condense (above right), and the other is to merge by gravity (or collide and merge, which will be introduced in the following on the left). I won't go into details here. The result of the growth of cloud droplets is that they become larger, and eventually exceed the lifting capacity of the updraft, and fall down to become precipitation. Therefore, it can be seen that in the entire process of cloud formation and rain, water exists and develops in the form of "drops", so the form of precipitation is also carried out in the unit of "drops". Where did the shape of the raindrop come from? Analyzing the force of raindrops is very important in exploring the shape of raindrops. In the process of falling, raindrops are mainly affected by three forces, namely surface tension, gravity and air resistance. Surface tension makes the water drop like a ball. At the same time, when two water droplets meet, adhesion will occur, and under the action of surface tension, a new and larger water droplet that is approximately spherical will be formed. The second is gravity. Will gravity cause water droplets to stretch and deform? Yes, but not because of the law of free fall. The tearing caused by the law of free fall is useful only when objects fall in a sequence, but the entire raindrop starts to fall at the same time, so the acceleration process is also synchronized, and it will not cause the upper and lower parts of the water droplets to be affected by different speeds. Separate. So how does gravity work? Through static pressure. We can analyze the shape of the water drop by the stress balance between the inside and outside of the water drop. Inside the water drop, the static pressure is generated due to the presence of gravity, while the outside has surface tension and air resistance. How the internal and external pressures are balanced gives us a glimpse into the shape of the raindrop. . The simulation results show that the real shape of raindrops is close to an ellipsoid. Due to air resistance, the lower part of the ellipsoid becomes flat. When the raindrops are relatively small, the influence of air resistance is not significant, and the surface tension is dominant. However, as the size of the raindrops increases, the influence of air resistance gradually appears, and the flatness becomes obvious.
underwater, reef, marine biology, fish, coral reef, coral reef fish
Photo by greg89maryanto Source from Organism Background
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