Water vapor facts for kids
Water vapor is simply water in the form of a gas. You can't see it because it's invisible! It's a very important part of Earth's water cycle, which is how water moves all around our planet.
When liquid water gets hot enough, like when it boils at 100 degrees Celsius (212 F), it turns into water vapor. This is why you see steam coming from a boiling pot. Water vapor can also form directly from ice without melting first; this process is called sublimation.
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What is Water Vapor?
Water vapor is the gaseous state of water. Unlike liquid water or ice, water vapor spreads out to fill any space it's in. It's made of tiny water molecules that are far apart and moving very fast.
How Water Vapor Forms
The most common way water vapor forms is when liquid water heats up and evaporates. Think about a puddle drying up on a sunny day – the water is turning into invisible water vapor. When water reaches its boiling point, it turns into vapor much faster.
Another cool way water vapor forms is through sublimation. This happens when ice or snow turns directly into a gas without first melting into liquid water. You might see this happen with ice cubes that slowly get smaller in the freezer, even if they don't melt.
Water Vapor in Our World
Water vapor plays a huge role in our daily lives and in the Earth's climate. It's everywhere, even if you can't see it!
Water Cycle and Humidity
Water vapor is a key part of the water cycle. Water evaporates from oceans, lakes, and plants, rises into the air as vapor, forms clouds, and then falls back to Earth as rain or snow.
The amount of water vapor in the air is called humidity. When humidity is high, the air feels sticky and damp. When it's low, the air feels dry. Humidity affects our weather and climate, influencing how hot or cold it feels and whether it will rain.
Steam, Clouds, and Fog
It's easy to get confused between water vapor, steam, and clouds. True water vapor is invisible. What you see as "steam" coming from a kettle, or what you see as clouds or mist, is actually tiny liquid water droplets or ice crystals that have formed when water vapor cools down and condenses. These tiny droplets are visible, but the pure water vapor itself is not.
Water Vapor and the Greenhouse Effect
Water vapor is a very important greenhouse gas. Greenhouse gases trap heat in Earth's atmosphere, which keeps our planet warm enough for life to exist. Without these gases, Earth would be a frozen ball of ice. Water vapor is the most abundant greenhouse gas and naturally helps regulate Earth's temperature.
Images for kids
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Clouds, formed by condensed water vapor
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Evidence for increasing amounts of stratospheric water vapor over time in Boulder, Colorado.
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Cryogeyser erupting on Jupiter's moon Europa (artist concept)
See also
In Spanish: Vapor de agua para niños
