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Water power and dams

الأسبوع 21 · المحور الثالث، الوحدة الثالثة، المفهوم 3.3 «مصادر الطاقة المتجددة» (ب) ومشروع الوحدة «آثار السدود» · 3 دروس
1

Falling water makes electricity

Discovery Education Science P4: Term 2, Unit 3, pp. 70–83
GoalExplain how falling water makes electricity in a hydroelectric power station and compare it with wind power.
New words
hydroelectric power · electricity made from the energy of moving waterturbine · a wheel with blades that spins when water or wind pushes itgenerator · a machine joined to a turbine that makes electricity when it spins
Explanation

Rivers run downhill. Water high up has stored energy, which we call potential energy, and when it falls the stored energy changes into kinetic energy, the energy of motion. A dam is a strong wall built across a river. It holds the water back, so the water behind it stays high. When the gates open, the water rushes down through tunnels and pushes the blades of a turbine. The turbine spins a generator, and the generator makes electricity. Wires carry the electricity to homes, schools and factories. This is called hydroelectric power. Wind power is similar: moving air pushes the blades of a wind turbine. Both use moving energy that nature gives again and again, and neither burns a fuel. They differ in what moves: air for wind, water for a dam.

Worked examples
high waterwheellamp
Youssef’s class visits a model of a dam in a science museum. A tank of water sits high up. When a tap is opened, the water drops onto a small wheel and the wheel spins a tiny generator that lights a lamp. The high water is the stored energy.
The energy chain of a hydroelectric power station has four links. Water high up has potential energy. Falling water has kinetic energy. The spinning turbine has kinetic energy too. The generator changes it into electrical energy.
QuestionWind powerWater power
What moves?airwater
What spins?wind turbinewater turbine
What makes the electricity?a generatora generator
Mariam makes a chart to compare two ways of making electricity without burning fuel. Both use the energy of something that moves, and both need a place that suits them: a windy hill or a river with a drop.
Class activity

Compare and draw. Fold a page in half. On the left draw a wind turbine with an arrow for the wind. On the right draw a dam with an arrow for the falling water. Under each, write what moves, what spins and what makes the electricity. Colour the things that are the same in both drawings. A grown-up checks your chart.

Practice
1
What is a dam used for in a hydroelectric power station?
2
Put the steps in order: A the generator makes electricity, B water falls through a tunnel, C water waits high behind the dam, D the turbine spins.
3
A dam has 4 turbines. Each makes 5 units of electricity every hour. How many units do they make together in one hour?
4
Name one thing that is the same and one thing that is different between a wind turbine and a water turbine.