School › Water cycle › Ages 10–11
The water cycle: evaporation, condensation and precipitation
The key steps of the water cycle, where Earth's water is stored, and the role of the Sun and gravity. With a fair test on what makes water evaporate faster.
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The water on Earth is always moving between the oceans, the air and the land. This never-ending journey is the water cycle. It is powered by energy from the Sun and by gravity.[1][4]
Evaporation changes liquid water into a gas, water vapour. Heat from the Sun makes water evaporate from oceans, lakes and the ground. Plants also release water vapour through their leaves: this is called transpiration. About 90% of the water in the air comes from evaporation and about 10% from transpiration.[2][4][3]
As air rises, it cools. In the cooler air higher up, some of the water vapour turns back into tiny liquid droplets. This is condensation, and it forms clouds.[4][3]
In a cloud, droplets bump into each other and merge into bigger drops. When they are heavy enough they fall as precipitation: rain, sleet, snow or hail. On average the whole world gets about 980 mm of precipitation each year.[4][2][5]
Gravity pulls the water downhill. Some flows over the ground as runoff into streams and rivers, and most of it ends up back in the sea. Some soaks into the ground (infiltration) and is stored as groundwater in the cracks and pores of rocks.[2][1][5]
Over 96% of Earth's water is in the oceans. Only a tiny amount, about 0.001%, is in the air at any moment: if it all rained out at once, it would cover the Earth only about 2.5 cm deep.[2][3]
Try it: Fair test: what makes water evaporate faster?
You need
- Four identical small dishes or jar lids
- A measuring jug or syringe
- A ruler
- Water
- A sunny or warm spot and a cool, shady spot
Safety
Use plastic dishes if possible, and don't put glass where it can fall. Wipe up spills so nobody slips. Don't drink the water.
What to do
- Put exactly the same amount of water (for example 50 ml) in each dish.
- Choose ONE thing to change: put two dishes in a warm, sunny place and two in a cool, shady place.
- Keep everything else the same: same dishes, same amount of water, same start time, no lids.
- Predict which dishes will lose water fastest.
- Each day at the same time, measure the depth of water with a ruler (or pour it into the jug to measure).
- Compare the results. Was your prediction right?
What happens, and why?
Warmth gives the water energy to evaporate, so the dishes in the warm place lose water faster. Changing only one thing (the place) and keeping everything else the same makes the test fair, so you know the difference was caused by the warmth. Using two dishes for each place lets you check that your results repeat.[4][5]
Play: Name that step
Which step of the water cycle is this? Choose the right one.
Your best score is kept only on this device. Nothing is sent anywhere.
Quiz
Other ages: Ages 6–7 · Ages 15–16