Why Clouds Don’t Fall

A clear blue sky, fluffy white clouds, and vast green fields—this is one of the most picturesque scenes in our imagination. Sometimes, as you lie on the grass, watching the clouds drift by, a curious thought crosses your mind: **How much does a cotton candy-like cloud weigh? Could it ever suddenly fall from the sky?**

Don't be fooled by their soft, dreamy appearance—each cloud can weigh hundreds of tons! Clouds are a crucial part of Earth's water cycle. When the sun heats the Earth's surface, water evaporates, turning into water vapor that rises into the sky with air currents. As it ascends, the temperature drops—on average, by **0.65°C for every 100 meters of elevation.**

At a certain temperature, the water vapor condenses when it meets cold air, gathering around dust particles to form tiny droplets. These droplets accumulate to create clouds. Even a medium-sized cloud can weigh **more than 500 tons**. With such a massive weight, how do clouds remain suspended in the sky instead of falling due to gravity?

### Why Don't Clouds Fall from the Sky?

Water molecules consist of one oxygen atom and two hydrogen atoms. The Earth's atmosphere is mainly composed of nitrogen and oxygen, both of which are heavier than hydrogen. This makes water vapor **lighter than air**. Since equal volumes of gases contain the same number of molecules at the same temperature and pressure, regions with high concentrations of water vapor are **lighter** than the surrounding air, causing water molecules to rise.

However, no matter how light they are, water molecules are still subject to **gravity**. This means that clouds, too, experience the Earth's gravitational pull. The reason they don’t fall immediately lies in **terminal velocity**—a concept in physics that describes how fast small objects, like water droplets, fall through the air. The smaller the object, the slower it falls. Since cloud droplets are **extremely tiny**, they fall at a rate so slow that they appear to **float in the air**.

Even though these droplets do eventually descend, they often **evaporate before reaching the ground**, rising again to form new droplets. This continuous process keeps clouds in a state of **dynamic balance**.

### Why Do Clouds Sometimes Bring Rain, Snow, or Hail?

The answer lies in **temperature and atmospheric conditions**.

At high altitudes, the water droplets in clouds often exist as **ice crystals or snowflakes**. A small, isolated cloud won’t generate enough energy to cause rain. However, when **many clouds gather**, strong air currents create **turbulent convection**. Ice crystals collide, rub against each other, and grow heavier until they become too heavy to stay aloft, eventually falling as precipitation.

If the temperature **near the Earth's surface is above 0°C**, the falling ice melts and turns into **rain**.

Some might wonder: "Why do we sometimes get **snow or even hail in summer**?" This happens because of **extreme weather conditions**. In **summer**, strong convective air currents frequently occur, forming massive **cumulonimbus clouds**. These towering clouds can reach heights of over **10,000 meters**, where temperatures drop to **-30 to -40°C**.

Within these clouds, **supercooled water droplets** exist in a liquid state despite being below freezing. As **updrafts** push these droplets higher, they encounter ice crystals and snowflakes, **freezing upon contact to form hailstones**.

These hailstones cycle **up and down** within the cloud, accumulating more layers like a snowball. Eventually, when the **updrafts can no longer support their weight**, they plummet to the ground as **hail**.

### The Ever-Changing Beauty of Clouds

Clouds bring the essence of each season to life. **In summer, the sky is a deep, brilliant blue; in autumn, fluffy white clouds float serenely; in winter, dark clouds shroud the setting sun; and in spring, gentle breezes push clouds across the sky.**

So next time you have a moment to spare, look up. You might just find a cloud that captures your imagination.