Science
What is evaporation?
Quick answer
Evaporation is when a liquid slowly turns into a gas from its surface, like a puddle drying in the sun. It happens faster when it is warm, windy or the liquid is spread out.
In one sentence
Evaporation is when a liquid turns into a gas, usually slowly and from its surface, such as when a puddle dries up.
Explained
Liquids are made of tiny particles that are always moving. Some particles at the surface move fast enough to break free and escape into the air as a gas. When this happens to water, the gas is called water vapour. You can't see it, but it is there.
Think of a crowded swimming pool. Most swimmers stay in, but every now and then someone with lots of energy climbs out. Over time, the pool gets emptier. That is evaporation.
Evaporation speeds up when:
- It is warmer. Heat gives particles more energy, so more escape.
- It is windy. Wind carries the vapour away, making room for more.
- The surface is bigger. Water spread out on a plate dries faster than water in a narrow glass.
- The air is dry. In humid weather, the air already holds lots of vapour, so things dry slowly.
Boiling is a faster, hotter change. At 100°C at sea level, water turns to gas all through the liquid, not just at the surface, making big bubbles.
Evaporation also cools things down. When sweat evaporates from your skin, it takes heat with it. That is how your body keeps cool on a hot day.
Evaporation is the first step of the water cycle, lifting water from the sea into the sky.
Examples
- Wet washing drying on a line.
- A puddle shrinking in the playground.
- Salt left behind when seawater evaporates in a dish.
- Feeling cool after swimming when you stand in the breeze.
- A drop of nail varnish remover or hand sanitiser drying in seconds.
sun
wind
T-shirt
Common mistakes
- "The water has disappeared." It hasn't. It is in the air as water vapour.
- "Evaporation only happens when water boils." It happens at any temperature, just more slowly when cool.
- "Evaporation and boiling are the same." Evaporation is slow and only at the surface. Boiling is fast and happens throughout the liquid.
Quick quiz
Evaporation
Check what you know with 4 quick questions.
Question 1 of 4
What happens to water when it evaporates?
Practise it
Try it
Put the same amount of water in a saucer and a narrow glass. Mark the levels and check each day. Then learn how evaporation changes states of matter.
Weather and water activities
For grown-ups
Related topics
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The water cycle is the endless movement of water between the land, the sea and the sky. Water evaporates, condenses into clouds, falls as rain or snow and collects in rivers and oceans.
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