The clouds that we can see every day when we look up, hang lightly in the sky like cotton.
This makes some people take it for granted that the cloud is very light, otherwise it must have fallen! In fact, any cloud in the sky may weigh dozens to hundreds of tons!
Some meteorologists say that a cloud with a diameter of about 1 km can have a mass of 500 tons, which is equivalent to 4 adult blue whales or more than 70 adult African elephants!
A piece of cloud can be several kilometers long, and a small one can be hundreds of meters, which means that the quality of the clouds above our heads is far beyond our imagination!
But how did such a heavy cloud get in the air?
To answer this question, we need to understand how clouds are formed.
To put it simply, there is water vapor in the atmosphere, which liquefies into small liquid droplets when it is cooled in the air, or condenses into small ice crystals, and they gather more and more slowly to form visible polymers in the air. This is the cloud you see. It has a large mass and a larger volume, that is, it has a very low density.
The cloud will fall under the force of gravity, and will fall faster and faster. Clouds are also affected by air resistance, which gradually increases as the falling speed increases.
But these two variables are not the only ones. The flow of air and the continuous rise of hot air will exert external forces on the small droplets in the cloud, making them "lighter", so light that they hang in the sky when they float.
Let's briefly talk about the impact of these "forces" on small droplets from a scientific point of view.
At high altitude, a layer of air is attached to the surface of the small droplets in the cloud, which can be regarded as a stable "shell". The air outside the "shell" blows over the small droplet, which creates a relative flow velocity for it. The speed difference between the two kinds of air "shell" and "outside the shell" creates friction that hinders the fall.
The scientific name for this friction is "viscous drag".
At the same time, the small droplets in the cloud are also affected by their own gravity and air buoyancy. When the two of them and the "viscous drag" are in balance, the velocity of the small droplet is proportional to the square of the radius.
* Simple conclusion, Xiao Heng will not put the formula here
That is, if the object has a small radius, the falling speed is also small. This speed also has a scientific name, "tail speed".
So when there is no updraft, the clouds will fall down, but the speed is very ~very~slow~
And everyone is familiar with "falling clouds".
How did the rain and snow fall? Because they are too heavy to hold the air~
