How can dark clouds weighing millions of tons float in the sky? Is it that the law of gravity has failed?

This article is based on answering questions raised by netizens: I heard that clouds weigh several tons, so how do they float in the air? Wouldn’t gravity fail?

Clouds float in the sky, which means they float above the air. This has something to do with gravity, but not much. Gravity manifests itself as gravity on the surface of the earth. The same mass of air and clouds have the same gravity.

The expression of universal gravitation is: F=GMm/r^2. Here G is the gravitational constant, that is, the gravitational value when two 1 kg objects are one meter apart, which is about 6.67*10^−11N⋅m^2/kg^2; M and m refer to the mass of the two objects that have gravitational effects on each other, in kilograms; r is the distance between the centers of mass of the two objects that have gravitational effects.

From the universal gravitation formula, we can see that gravity is an interaction, which is the manifestation of the interaction between two or more objects; the magnitude of gravity is proportional to the mass and inversely proportional to the square of the distance between the interacting objects. On the earth or other celestial bodies, gravity is presented in the form of gravity.

Gravity is not completely equivalent to attraction. As a celestial body, its mass is fixed, and its attraction is also fixed. However, due to the rotation of the celestial body, the centrifugal force at different latitudes is different, resulting in the difference in gravity. The higher the latitude, the greater the gravity, and the lower the latitude, the smaller the gravity. However, this difference is small. The g value of gravity on the surface of the earth is usually expressed as 9.8N/kg. In reality, at 0 degrees latitude at the equator of the earth, the gravity is 9.79N/kg; at 90 degrees latitude at the poles, the gravity is 9.83N/kg.

That is to say, for a 1kg object, at 0 degrees latitude at the equator, the gravitational force is only 9.78N; but at 90 degrees latitude at the poles, it is 9.83N.

As for gravitational force and gravity, the gravity of clouds and air of the same mass is equal. But why can clouds float on the air? This involves the theory of buoyancy. Buoyancy is a force opposite to gravity. It refers to the vertical upward force of the fluid on an object immersed in a fluid. It is the resultant force formed by the difference in fluid pressure on each surface of the object in a liquid or gas.

This theory was discovered and created by the ancient Greek philosopher and scientist Archimedes more than two thousand years ago. Its definition formula is Ffloat=Gdisplacement, and the derived formula is Ffloat=Gdisplacement=ρliquidgVdisplacement....These formulas are cumbersome to explain. Now I would like to explain it in a simple way. The essence of buoyancy is actually a phenomenon caused by the density difference of objects under gravity conditions.

Density is an indicator that measures the relationship between the mass and volume of an object. Its symbol is ρ, and its unit is generally kg/m^3 (kilograms per cubic meter) or g/cm^3 (grams per cubic centimeter). Under the gravitational conditions of the earth or other celestial bodies, objects with higher density will sink in the fluid, and objects with lower density will float.

For example, the density of water is 1000kg/m^3, while the density of dry wood is generally between 400 and 600kg/m^3, so it will float on the water; other objects that are lighter than wood, that is, with a lower density, are more likely to float on the water. But some people may wonder, the density of steel is much greater than that of water, so why can a 10,000-ton ship float on the water?

Yes, the density of carbon steel is about 7850kg/m^3, which is 7.85 times greater than the density of water. Why do ships made of steel float? Here is a reminder that density refers to the relationship between volume and mass, and is a measure of the mass of a specific object within a certain volume. According to this principle, let's think about it. Although the ship is made of steel, people make it into a large hollow volume, so the overall density is greatly reduced.

That is to say, whether it is a small boat or a 10,000-ton ship, whether it is made of steel or other materials, its volume is very large. For example, if 100,000 kg of steel is used to make a ship with a volume of 1,000 cubic meters, what is the density of such a ship? Let's calculate: 100,000/1,000=100, which means the density is 100 kg/m^3, and the density of water is 1,000 kg/m^3. In this way, of course the ship can float, and it can also carry a lot of cargo.

Having said that, I believe everyone should understand why clouds can float in the air, right?

Simply put, clouds are a phenomenon caused by the huge water circulation system on the earth's surface. Under solar radiation, water on the earth's surface is evaporated to form water vapor. When the water vapor is in an oversaturated state, water molecules will gather around the dust in the air, producing water droplets or ice crystals that scatter sunlight in all directions, which allows us to see colorful clouds.

Why does water vapor rise? Because the density of saturated water vapor is 0.6kg/m^3, while the density of air is about 1.29kg/m^3, so of course water vapor rises. When these water vapors condense into water droplets or ice crystals, as individuals, their density is greater than that of air, but in the huge volume of water vapor, the overall density is very low, even falling below 0.5kg/m^3.

In addition, the thermal expansion and contraction effect causes the hot air on the ground to rise continuously, which supports these small water droplets and ice crystals. In weather with strong convection, these small water droplets and ice crystals are constantly pulled down by gravity and lifted up by the hot air. They become larger and larger in the constant collision. Finally, the hot air can no longer bear the burden and cannot support them, so heavy rain or hail falls.

If you cut open a hailstone, you will see its layered structure. This is the result of being "manipulated" by gravity and hot air and constantly rolling up and down in the air.

The weight of a cloud is measured by its volume. It is a big underestimation to say that a cloud weighs several tons. A cloud is several kilometers in size. Even a cloud that is one kilometer square would weigh 500,000 tons based on a density of 0.5kg/m^3. The same volume of air weighs 1.29 million tons. Therefore, no matter how heavy a cloud is, it can only float in the air, while the air can only sink below.

I wonder if you are satisfied with this answer? Welcome to discuss.

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