Class 5 EVS · Chapter 7

7. Energy—How Things Work

Answers to all Write, Discuss, Find out, Activity and Let us reflect questions. NCERT Our Wondrous World, Class 5 EVS (CBSE) · Unit 4: Things Around Us.

What is Energy?

Observe a kitchen. Write your observations and the questions that come to your mind.

I Observe	I Wonder
The food is getting cooked.	How is it being cooked?
The pressure cooker whistles.	What makes the cooker whistle?
The fridge keeps milk cold.	How does the fridge cool things?
The mixer grinds chutney.	What makes the blades spin?
The bulb gives light.	How does the bulb glow?

From your observation, write at least three things that you have noticed:

Moving: fan, car, bicycle
Providing light: the Sun, bulb, torch
Making a sound: bell, radio, TV
Making things cool: fridge, cooler, AC
Making things hot: gas stove, iron, heater

Discuss: What makes these things move, shine, make a sound or get warm and cold?

Energy makes them work. They get this energy from electricity, fuel, food or the Sun.

Activity 1

Balloon Air Rocket: What would you change to make the toy move faster or slower?

Faster: Blow more air into the balloon. Keep the string tight and smooth.

Slower: Fill less air in the balloon, or keep the string loose.

Activity 2

Rubber Band Guitar: What happens if you use thinner or thicker rubber bands? Do they sound different?

Yes, they sound different. Thin rubber bands make a high (sharp) sound. Thick rubber bands make a low (deep) sound.

Activity 3

Sun-powered Water Warmer: Touch the water in both cups. What do you notice?

The water kept in sunlight is warmer. The water in the shade is cooler. The Sun gives heat energy.

Write

How is food cooked in your house?

Food is cooked on a gas stove using LPG (cooking gas). We also use a pressure cooker and an electric induction stove.

Discuss

1What kind of fuel do you use at home for cooking?

We use LPG (cooking gas).

2What are the problems of using too much wood or coal?

They give out smoke that pollutes the air. Smoke causes coughing and eye problems. Cutting trees for wood harms forests. Coal is also limited and will run out.

Activity 4

aWhich diya burns longer? Why?

Diya 2, with oil, burns longer. The oil keeps the wick burning. The dry wick in Diya 1 burns out quickly.

bWhat is acting as a fuel here?

Oil is the fuel.

Electricity

What are the things in your home that need electricity to work?

Fan, bulb, TV, fridge, mixer, iron, washing machine and mobile charger.

Activity 5: Identify things that run on electricity. Fill in the table.

S. No.	Device	What it does?	What it requires?
1.	Fan	Blows air	Movement
2.	Tube light	Gives light	Light
3.	Television	Shows pictures with sound	Light and sound
4.	Refrigerator	Keeps food cool	Cooling
5.	Electric iron	Removes creases from clothes	Heat
6.	Mixer	Grinds food	Movement

What would your day be like if there was no electricity at all?

There would be no fans or lights. We could not watch TV or charge phones. The water pump would not run. Food in the fridge could spoil. Studying at night would be hard.

Can you find out the sources that produce electricity without pollution?

The Sun (solar energy), the wind and flowing water.

Generating Energy from the Sun, Wind and Water

Place one damp cloth in the Sun and another in the shade. Which one will dry first? Why?

The cloth in the Sun dries first. The Sun’s heat makes the water evaporate faster.

Activity 6 — Pinwheel: What happens to your pinwheel?

The pinwheel spins (rotates). The moving wind gives it energy.

Activity 7 — Sunlight in Focus: What happens to your paper?

The paper becomes hot at the bright spot. It turns dark and starts to burn. Focused sunlight gives a lot of heat.

Activity 8 — Water Wheel: Does the water make the wheel move?

Yes. The falling water pushes the spoons, and the wheel turns.

Write

Can you think of more examples where we use the Sun, the wind or the flowing water?

Sun: drying grains, chillies and clothes; solar cookers; solar water heaters.
Wind: sailing boats, flying kites, winnowing grain, windmills.
Flowing water: watermills (gharats) to grind grain, making electricity at dams.

Energy All Around Us: List the actions you see in the picture and fill in the table.

Activity	Source of Energy
A child carrying a school bag.	Food
A man carrying a heavy sack.	Food
A farmer ploughing with a tractor.	Fuel (diesel)
A car and a scooter moving on the road.	Fuel (petrol)
A woman drying grains in the Sun.	Sun
Clothes drying on a line.	Sun and wind
Windmills turning.	Wind
A man switching on the light.	Electricity

Activity 9

Energy Flow Game

Find your match of source, type and use. Examples: Food → Movement → Running; Fuel → Heat → Cooking; Electricity → Light → Lighting a bulb; Water → Movement → Turning a turbine.

Let us reflect

1What will happen if there is no electricity in your house for a day?

Fans, lights, TV and the fridge will not work. We cannot charge phones or run the water pump. It will be hard to study at night.

2Why is it better to use solar or wind energy instead of coal?

Solar and wind energy are clean. They do not give out smoke or harmful gases. They will never run out. Coal pollutes the air and will run out one day.

3Give two examples where you have seen energy being stored.

A battery in a torch or toy stores energy.
Our body stores energy from food for later use.

4What is the one thing you can do at home to save energy?

I will switch off lights and fans when I leave a room.

5Find out how many kilometres a vehicle travels per litre of petrol or diesel. How will you compare them?

Motorcycle — about 50 km per litre

Car — about 15 km per litre

Bus — about 4 km per litre

A vehicle that goes more kilometres on one litre uses less fuel. But a bus carries many people, so it saves fuel per person.

These are rough figures. Ask elders about the vehicles you know.

6List any three objects that use energy and mention their source of energy.

Fan → Electricity
Gas stove → Fuel (LPG)
Torch → Battery
Bicycle → Food (our body)

7Create and share: (a) a ‘clean energy home’ plan, (b) ‘my energy diary’ for one day.

(a) Draw a house with solar panels on the roof, a small windmill, big windows and a solar water heater. (b) Note each time you use electricity, fuel or the Sun during one day.

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