Evaporation & Condensation

Wet clothes dry. Cold glasses get droplets. Both are the same trick — water sneaking between liquid and gas. This 90-second narrated lesson teaches kids about evaporation and condensation, the engines of the entire water cycle. Includes a quiz.

Class 6 ScienceClass 6 / Grade 6Ages 8–11
Lesson
💨 Evaporation & Condensation
Wet clothes dry — but where does the water go?

When you hang wet clothes outside, they get dry. The water doesn't run out and drip away — it just disappears. So where did it go? The answer is — straight into the air, as invisible water vapour.

What is evaporation?

Evaporation is when liquid slowly turns into gas — but unlike boiling, it can happen at any temperature. At the surface of any liquid, some particles always have enough energy to break free and fly into the air as vapour. Sun and wind speed this up dramatically. That's why washing dries faster on a hot, breezy day than on a cool still one.

What is condensation?

Condensation is the reverse — gas turning back into liquid. When warm air full of water vapour touches a cool surface, the vapour particles slow down and stick together as tiny liquid droplets. Take a cold glass out of the fridge and droplets appear on it within seconds — that's water vapour from the air condensing on the cool surface.

Where you've seen it

  • Wet clothes drying on a line — water evaporates into the air
  • Sweat cooling you down — sweat evaporates from your skin, and that pulls heat away
  • Morning dew on grass — water vapour in the cool morning air condenses on cold blades of grass
  • Misty windows in winter — warm indoor vapour condenses on cold glass
  • Steamy bathroom mirrors — vapour from your hot shower condenses on the cool mirror
  • Clouds — water vapour high in the sky cools and condenses into the tiny droplets that make a cloud

Two transitions, one engine

Evaporation and condensation always happen together in nature. Heat causes water to evaporate from oceans and lakes. The vapour rises high, cools, and condenses into clouds. Eventually the clouds drop the water back as rain. Without these two opposite tricks, our planet wouldn't have rain at all.

Frequently asked questions

What's the difference between evaporation and boiling?

Boiling is fast and noisy — water at 100°C with bubbles forming throughout. Evaporation is gentle, happens at any temperature, and only at the surface. Both turn liquid into gas, but evaporation is the slow version.

Why does sweating cool you down?

When sweat evaporates from your skin, it takes heat away with it. That's evaporative cooling. The same trick is why splashing water on yourself feels refreshing on a hot day.

Where does the water on a misty window come from?

From the air inside the room. Warm air can hold a lot of water vapour. When that vapour-rich air touches a cold window, the air cools, can't hold as much vapour, and the extra condenses on the glass as tiny liquid droplets.

Why do clouds form?

Water evaporates from oceans, lakes and rivers, rising into the sky as invisible vapour. Higher up, the air is much colder. The vapour condenses on tiny dust particles, forming millions of tiny water droplets — that's a cloud.

Why does washing dry faster on a sunny, windy day?

Sun heats the water, giving particles more energy to evaporate. Wind blows away the air right above the cloth, replacing it with drier air that can absorb more vapour. Both factors speed up evaporation.

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