Class 5 Environmental Studies Chapter 7: Energy — How Things Work

Ten minutes in the kitchen

Kabir sits on a stool in the kitchen with a notebook. His teacher has asked the class to watch something closely for ten minutes. He writes what he sees. The cooker hisses. The mixer whirrs. The tube light glows. The fridge hums, and inside it the water is cold. Kabir writes one more line: what is making all of this happen?

The word for all of it

Things move. Things light up. Things make sounds. Things grow warmer or cooler. Something must make each of these happen. We call that something energy. Energy is the reason things move, glow, make sound, do work, and grow warmer or cooler.

Five jobs, one idea

Look for the five jobs around you. A fan turns, so there is movement. A bulb glows, so there is light. A bell rings, so there is sound. A stove heats the dal. A fridge cools the water. Every one of them needs energy.

The great giver

The Sun gives us light. The Sun also gives us heat. Clothes dry on the line because of it. Papads dry in it. Plants grow in it. Nearly every living thing here depends on it.

The racing balloon

Kabir blows up a balloon and pinches the neck shut. Then he lets go. The balloon shoots across the room. Air rushes out of it, and that rushing air pushes the balloon forward. Moving air can push things along.

A guitar from a box

He makes a hole in a carton and stretches rubber bands across it. A pencil under the bands lifts them. He plucks a band. It shivers quickly, and a note fills the room. That shivering is called vibration, and vibration makes sound.

Thick band, thin band

Kabir tries a thin band and then a thick one. The notes are not the same. A thin band gives a higher note. The fun is in trying: pluck, listen, change one thing, pluck again.

Two cups and a sunny step

He fills two cups with water. One waits on a sunny step. The other waits in the shade. After twenty minutes he dips a finger in each. The sunny cup is warmer. Sunlight has given its water heat.

You see what energy does

Energy is not a thing you can hold in your hand. You cannot pour it into a bottle. You notice it by what it does. A turning wheel, a glowing lamp, a ringing bell and warm water all tell you that energy is at work.

Cooling needs it too

Children often think only hot things use energy. A fridge shows that this is not so. It runs on electricity all day, and it uses that energy to take heat out and keep the food cool. Warming and cooling both need energy.

Scenario:

A class lists everything in the room that needs energy. The list reaches nineteen items, from the fan to the children themselves. Ravi says only the machines need it. His teacher asks the class to test that by sitting completely still for two minutes. They are still breathing, and still warm. The class adds themselves back to the list. They then sort the nineteen items by what each one does with the energy: moving, glowing, making sound, or growing warmer. Meena notices that some items do two of those at once, such as a bulb that lights and heats.

Analysis:

Sitting still settles it. Breathing and staying warm both continue, so a living body is using energy even when it is doing nothing visible.

Activity:

List ten things around you that need energy. Mark what each one does with it, and circle any that do two things.

Title:

The box guitar

Safety:

An adult should do the cutting. Do not stretch a band near your face or anyone's eyes.

What You Notice:

Each plucked band shivers quickly and a note is heard. A thin band gives a higher note than a thick one. The shivering is vibration, and vibration is how sound is made.

Your brain keeps using energy while you sit still, and even while you sleep.

Air rushing out of a balloon can pull it along a string, like a tiny rocket on a wire.

What energy does — MOVE, LIGHT, SOUND, WARM — Four words for four signs that energy is at work around you.

Energy is invisible — You see the doing, not the energy — A turning fan or a glowing bulb is the clue; the energy itself is never seen.

Jump, run, sit down

The teacher asks the class to stand and stretch. Then jump. Then run on the spot. Everyone flops back on the bench, laughing. "How were you able to move?" she asks. Hands go up. "Energy, teacher!" She smiles and asks the next question. "And where did that energy come from?"

Food is the answer

Kabir remembers his morning idlis. When he skips breakfast he feels dull by the second period. After a meal he is ready to play again. Food gives us the energy we need. It is a source of energy for every living thing.

Animals eat for the same reason

A dog runs down the lane. A kite circles high above. A buffalo walks to the pond. They all move, fly, swim and hunt. Their energy comes from food too, just as ours does.

Energy kept for later

Our body does not use up every bite at once. It stores some energy for later. That is why we can still walk and play after missing a meal. A torch does something similar. Its batteries hold stored energy until the switch is pressed.

What moves a scooter?

A scooter cannot eat idlis. Kabir's mother stops at a pump and fills the tank. Petrol and diesel are fuels. A fuel is something that is burnt to give energy. Fuel is to a vehicle what food is to us.

Fuels in the kitchen

Homes use fuel as well. Many kitchens run on cooking gas. In some places people cook on wood or coal. All of these are fuels, and all of them burn to give heat for cooking.

The two diyas

The class tries a test with the teacher. One diya holds a wick and no oil. The other holds a wick with oil around it. Both are lit by the teacher. The dry wick burns out quickly. The one with oil keeps burning. The oil is the fuel.

Smoke is the problem

Burning wood or coal gives heat, but it also gives smoke. Smoke makes the kitchen sting and the air dirty. It is not good for anyone who breathes it. So these fuels must be used carefully and never wastefully.

The food and fuel family

Put them side by side. Food gives energy to people and animals. Fuel gives energy to vehicles, stoves and lamps. Batteries hold energy until it is needed. Each one is a store that gets used up, so none of them should be wasted.

Even sitting still

The teacher ends with a surprise. Our brain keeps using energy while we sit quietly, read or sleep. The body never switches off completely. That is one more reason to eat well every single day.

Scenario:

A class is asked how long a person can go without food. Nobody is sure. Their teacher asks a narrower question instead. Can you still run an hour after breakfast, and four hours after? The children know they can. So the body is not using food the moment it arrives. The class works out what that means. Some energy is stored, and the store is what keeps a body going between meals. Arjun then asks whether a machine does the same. The class compares. A scooter stops the moment its fuel runs out, because it keeps no store of its own.

Analysis:

The gap between eating and moving is the clue. A body stores energy and a scooter does not, which is why one keeps going and the other stops at once.

Activity:

Write what you ate today and when. Note the longest gap between a meal and running about, and what kept you going.

Title:

The energy hunt

Safety:

Only look. Do not touch a hot stove, a flame, a plug or a wire.

What You Notice:

Every working thing at home has some source of energy behind it. People and pets run on food, stoves and vehicles run on fuel, and a few things run on stored energy in batteries.

A torch keeps working in a power cut because its batteries already hold energy inside them.

A meal eaten at noon can still be giving a child energy at four in the afternoon.

Food and fuel — Food for us, fuel for machines — Both are stores of energy; one feeds a body, the other feeds a stove or an engine.

Smoky fuels — Wood and coal bring smoke and all — They give heat, but the smoke dirties the air we breathe.

The evening the lights went out

The power goes at seven in the evening. The fan stops. The tube light dies. The television falls silent. Kabir's little sister asks for her cartoon and then for a cold drink of water. Their grandmother lights a diya. "Now count," she says, "how many things in this house were waiting on electricity."

What electricity does for us

Kabir counts on his fingers. The fan gives movement. The bulb gives light. The radio gives sound. The iron gives heat. The fridge keeps food cool. One kind of energy, doing all five jobs, in every room.

Bigger than our homes

Schools and hospitals need it too. So do factories, where machines run on electricity. Those machines help make cloth, books, toys, food packets and even the vehicles on our roads. A power cut slows a whole town, not one house.

Electricity can be dangerous

Grandmother adds a warning. Never touch a wire or a switched-on device with wet hands. Never push a pencil or a finger into a socket. Stay far away from a broken wire or a fallen pole, and tell an adult at once. Do not play near an electric box.

Where does it come from?

Most of the electricity we use is made by burning coal. Coal burns in huge plants far away, and wires carry the electricity to our homes. Burning it sends up thick smoke along with gases that harm us. That dirty air is bad for us and for every living thing.

Cleaner ways to make it

Are there other ways? Yes, and Kabir has seen them all. Sunlight, wind and flowing water can be used to make electricity. None of them has to be burnt, so none of them fills the sky with smoke.

Panels that drink sunlight

Solar panels sit on rooftops and soak up sunlight. They turn it into electricity for lights, pumps and fans. The Sun charges no bill and sends no smoke. On a sunny roof, a panel works quietly all day.

Windmills and water wheels

A windmill's blades spin in the wind and make electricity. Fast-flowing or falling water can do the same. In some hill villages, a water wheel called a gharaat has turned with the stream for years and ground the grain.

Clean energy

Electricity made from the Sun, the wind or flowing water is called clean energy. It does not fill the air with smoke or leave heaps of waste. The more we use it, the healthier our air stays.

Doing the same job with less

There is a second way to help. A bulb that uses less electricity for the same light saves energy every hour it burns. Using less energy for the same work is called energy efficiency. Switching off a fan in an empty room saves it too.

Old houses knew this

Kabir's grandmother points at her own home. Its walls are thick and its windows small, so the rooms stay cool in summer and warm in winter. A courtyard lets in light and air. Such houses need far less energy all year.

The pledge on the wall

The lights come back at nine. Kabir writes a small list and sticks it on the wall. Switch off what nobody is using. Dry the clothes in the Sun. Ask for panels on our roof one day. Small habits, he decides, add up.

Scenario:

Ashwini's school has ten classrooms. Each room has two old bulbs. They stay on for six hours a day. The science club looks up the numbers. One old bulb uses 60 units of electricity a month. A new kind of bulb gives the same light for only 10 units. The headmaster asks the club to work out the saving first. The children draw a poster with their sums. They add a second idea as well. During the games period every classroom stands empty. Lights and fans should be switched off then. The panchayat is pleased with the poster. It promises solar panels for the school roof next year.

Analysis:

Numbers turn an idea into a decision. The children see that using less energy and choosing cleaner energy are two different, useful steps.

Activity:

Count the bulbs and fans in your own classroom. Find out how many hours a day they stay on.

Title:

A pinwheel that catches the wind

Safety:

An adult must handle the pin and the scissors. Keep the pin point away from your eyes.

What You Notice:

The pinwheel spins as the wind pushes its folded corners. Moving air carries energy. A windmill works on the same idea, but its spinning is used to make electricity.

Some airports and railway stations in India now run largely on electricity made from sunlight.

Rajasthan has one of the world's largest fields of solar panels, spread over dry open land.

Sources of clean energy — SUN, WIND, WATER — Three givers of electricity that never send smoke into the air.

Electrical safety — Dry hands, no pokes, tell an adult — Three rules that cover most of the dangers around wires and sockets.