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Evaporation, convection and a drop’s journey

الأسبوع 17 · الوحدة الثالثة، المفهوم 1.3 «انتقال الطاقة خلال دورة الماء» (ب): التبخر والتكثف والحمل الحراري · 3 دروس
3

The journey of one water drop

Science P6: Term 2, Unit 3, pp. 10–14
GoalTell the story of one tiny bit of water as it travels through the water cycle, saying where it gains and loses energy.
New words
gain energy · take in heatlose energy · give out heatjourney · a trip from one place to another
Explanation

Imagine one tiny bit of water in the sea near Alexandria. The Sun warms it, it gains energy and evaporates into the air. Warm air carries it upward by convection. High up it cools, loses energy and condenses on a speck of dust, and with billions of others it forms a cloud. The cloud moves with the wind. Later the droplets join and fall as rain. Gravity pulls them down onto land. The water runs off into a canal or soaks into the soil and is taken up by a plant, which sends it back as vapour by transpiration. Or it flows to the sea again. The journey never ends, and the water is used again and again.

Worked examples
StepGains or loses energy
evaporationgains
condensationloses
transpirationgains
In Farida’s story the drop evaporates, condenses, falls as rain, flows to a river and reaches the sea. She marks where it gains energy (evaporation) and loses energy (condensation).
Seif asks: could the same water have been in a dinosaur’s world? Yes. Water is recycled, so the water you drink has been in the cycle for a very long time.
rootstemleaf
Nour adds a plant to the journey: a drop enters a root, goes up the stem and leaves as vapour from the leaf.
Class activity

Write a drop’s story. Write a short story of about six lines about a drop from the sea, using the words evaporation, condensation, cloud, rain and gravity. Mark where it gains energy and where it loses energy. Read it to your family.

Practice
1
Where does a drop gain energy in its journey?
2
Where does a drop lose energy?
3
What pulls the rain down?
4
Put in order: rain, evaporation, cloud, condensation.