Page 90 - Science class 4

2. Wind

Movement of air around us is called
wind. Any object that is moving has

energy in it. Energy of the wind can turn

windmills which in turn can move other
machines called turbines . Turbines then
help to produce electrical energy.

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In villages, people use gobar (cow dung) gas as fuel for cooking and
lighting up homes.
3. Water

Moving water too has a lot of energy in it.

To use this energy, we build dams. Dams
allow the water to fall with force, from a

height, onto the turbines. They move and

help to produce electrical energy.

Scientific Terms
Groove : a hollow cut of 'V' shape, made on the surface
Inclined : at an angle to the horizontal position

Tightened : to make something fixed firmly
Loosened : not tied up
Windmill : a machine which runs on the energy by air
Screw Driver : a special tool to turn a screw

Chapter at a Glance

³ A pull or a push acting on an object is called force.
³ There are two main types of forces in nature–gravitation and friction.

³ Machines make our work easier.
³ The ability to do work is called energy.

³ Energy exists in various forms, such as : heat, light, sound, electrical,

mechanical and chemical energy.
³ Some sources of energy are the Sun, wind and water.

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