Everyone knows that clouds consist of small water droplets or ice crystals. Water droplets in the cloud are different in diameter from a fraction of a micrometer to several millimeters. No matter how small ice drop, it is still heavier than air. Therefore, a natural question arises: how water drop (along with the cloud in General) are held in the air and not fall to the ground? At the same time another question: under what conditions water droplets no longer stay in the air and fall to earth as rain?
Let's start with the smaller droplets, the radius of which is fractions of a micrometer. Such droplets are not allowed to fall down indiscriminate strikes by the air molecules that are in a chaotic thermal motion. This motion is called Brownian - named after the English botanist R. Browne, who discovered it in 1828 Blows air molecules are forced to drop bounce in different directions; eventually it moves through the quaint angled trajectory.
The heavier drop, the harder it is for air molecules to budge it, and, consequently, the smaller the role of Brownian motion. But this increases the influence of gravity. When the radius of the droplet becomes more of a micrometer, it ceases to be Brownian. The drop begins to fall under the force of gravity, gradually accelerating. And then begins to play a greater role in a new factor, preventing the drop down, the resistance of the air environment. Simultaneously with the acceleration of the droplets occurs and begins to grow, the current drop on the force of air resistance. It is directed opposite to the force of gravity and is proportional to the speed drops.
Increases resistance to the speed of the falling drops is growing slower. When the force of air resistance is aligned to the module with the force of gravity, to further increase the speed drops stops and the next drop falls evenly. Such a uniformly moving drop can slow and even toss up upward flow of warm air. And the earth, which heats the sun is a constant source of such rising air currents.
In addition, in the process of falling drop can simply evaporate. Or to share into smaller droplets.
But the drop may, on the contrary, consolidated: merge with others or to condense on its surface an additional steam and then it will fall to the ground. And precipitation. In a sense, you could even say that precipitation (rain or snow) is the fall of clouds on the earth, only really raindrop or snowflake too big and heavy, so they could be part of a cloud.
If in the rain to look at the cloud side,
it seems that she falls to the ground.