الأسبوع 16 · المحور الثالث «التغير والثبات»، الوحدة الثالثة «الماء والطقس والمناخ»: ابدأ، المفهوم 1.3 «انتقال الطاقة خلال دورة الماء» (أ) · 3 دروس
2
Where did the puddle go?
Science P6: Term 2, Unit 3, pp. 1–9
GoalExplain where a puddle goes, and show that much of it evaporates.
New words
evaporation · liquid water changing into invisible water vapourwater vapour · water as a gas in the airpuddle · a small pool of rain on the ground
Explanation
After rain a puddle forms on the pavement. By evening it has shrunk or gone. Where did the water go? Some soaks into the ground, but much of it evaporates. The Sun warms the water. The water changes from liquid to water vapour, an invisible gas, and mixes with the air. A hard, paved surface lets very little water soak in, yet the puddle still disappears. This shows that evaporation is the main cause. You can test it: draw a chalk line around a puddle and look again after some hours. The chalk shows how much smaller it has become. The water vapour is still around us, but we cannot see it. Later it will form clouds.
puddle of water→the Sun warms it→water vapour in the air
Worked examples
Time
Size of the puddle
9 o’clock
big, to the chalk
1 o’clock
much smaller
Seif draws chalk around a puddle at 9 o’clock. At 1 o’clock the edge of the puddle is far inside the chalk line.
Nour hangs one damp cloth in the sun and an identical one in the shade. The cloth in the sun dries first because the water there evaporates faster.
Omar wonders whether the water all sinks into the ground. He covers a small saucer of water with a thin plastic sheet. Next day there are drops under the sheet.
Class activity
Chalk the puddle. After rain, with a grown-up, draw a chalk line around a puddle. Look again in an hour, then in three hours. Draw the puddle each time. Also dry two cloths, one in the sun and one in the shade, and compare. Never promise a result: it depends on the weather.
Practice
1
What does the Sun do to the water in a puddle?
It warms it so it evaporates.
2
What is water vapour?
Water as an invisible gas in the air.
3
Why does the chalk line help us?
It shows how much smaller the puddle became.
4
Does all the water in a puddle sink into the ground?
