(science) How is the cloud floating in the sky? [english ver.]

Sometimes you would have seen these thoughts in the clouds above the sky.
　
　
　

'How can a cloud float above the sky?'
　　
　
　

We are in middle school, high school science hour
'Clouds consist of large and small water droplets, ice cubes, and water vapor formed by evaporated water vapor.' .
　
　
　

Because Newton's law of gravity is pulling the earth over the clouds, the clouds must fall to the ground.

But it does not fall. If you ask why,

'Could it be because the clouds are light?' I will answer.
　
　
　

But considering the size of the clouds is a strange answer.
　
　
　

Cumulus clouds usually begin to form at 500 m above sea level

Generally, in the case of cloudy clouds, the amount of ice cubes and water per cubic meter is about 1 g.
　
　
　

The cloud, about 1km in length, contains about 1000 tons of water.

Separate from the sky, why do not the guy with this massive weight fall.
　
　
　

To see this, we must think of the 'forces' acting on clouds.

Generally, the forces acting on the clouds are 'gravity', 'buoyancy', 'wind that acts on clouds'.
　
　
　

First, the weight of air in a volume of 1 m3 is about 1 kg = 1000 g.

If you have water droplets or ice cubes, you have 1 gram per cubic meter.

The volume of 1 m3 of cloud containing air is 1001 g.

Gravity is acting down to the ground 1001g.
　
　
　

Now let's look at buoyancy in the clouds.

Buoyancy is the force acting on an object in a fluid

When the buoyancy is greater than the gravity acting on the object, it floats up.
　
　
　

To check the buoyancy of the air, fill the box with a volume of 1 m3 on the balance and weigh the air.

If you subtract the weight of the box, you will have 0 g on the balance.

This is because the weight of the air is not zero but the gravity acting on the air equals the buoyancy acting on the air.
　
　
　

In other words, 1 m3 of air acts as a buoyant force of 1000 g, and the weight of the cloud is 1001 g.

The air buoyancy that can support the cloud is 1g shortage.

Considering that the weight of the pencil falling from the 63 building is 1 g

Clouds deserve to land well!
　
　
　

The clouds are actually falling. But the speed is too small to notice!

The weight of 1 g acting on a 1 m3 cloud acts on water droplets in the clouds

The speed at which drops of water fall by 1 g of gravity

Considering the cross-sectional area of falling droplets and the air resistance,

0.013 m per second, or 1 cm per second.
　
　
　

Eventually, the water droplets in the clouds are falling more slowly than the snails.

However, there is no day in which a wind of 1 cm per second does not blow.

Because the wind is easily made by the difference of the temperature or the pressure difference, the air surrounding the water drops

If you move with only 1 cm per second, the water drops will not fall but will be in place.

When the velocity of the ascending airflow is greater than 1 cm per second, the cloud can fly anywhere.
　
　
　

Conversely, when the weather is dry and there is a lot of downward currents, the clouds are scattered
I can see the clear sky like the autumn sky ~