Chapter 7: Energy — How Things Work
1. Chapter at a Glance
Around us, things move, light up, make sounds and get hot or cold. What makes all this happen is energy. Through fun activities like a balloon rocket, a rubber band guitar and water in the Sun, we see energy in movement, sound and heat.
Food is our source of energy, and animals also get energy from food. Vehicles get energy from fuels like petrol and diesel, and homes use cooking gas, wood or coal. Electricity runs fans, lights, TVs and factory machines, but it must be used safely. Most electricity comes from burning coal, which pollutes the air.
The Sun, wind and flowing water are natural sources of energy. Solar panels, windmills and fast-flowing rivers can make electricity without smoke or waste, which is called clean energy. The Sun is the main source of energy for life on Earth. We should save energy and choose clean sources whenever we can.
2. Word Meanings
| Word | Meaning |
|---|---|
| Energy | What makes things move, light up, make sound, do work and change temperature |
| Vibrate | To move quickly back and forth |
| Sound energy | Energy that we hear as sound |
| Heat energy | Energy that makes things warm |
| Source | The place from where something comes |
| Fuel | Something burnt to get energy, like petrol, wood or cooking gas |
| Pollution | Making air, water or land dirty and harmful |
| Electricity | A form of energy that runs lights, fans and machines |
| Transformer | A large electrical box that controls the flow of electricity |
| Energy efficiency | Using less energy to do the same work |
| LED | A type of bulb that gives bright light using less electricity |
| Solar panel | A panel that turns sunlight into electricity |
| Windmill | A machine that uses wind to turn blades and make electricity |
| Turbine | A wheel turned by wind or water to make electricity |
| Clean energy | Energy from the Sun, wind or water that does not pollute |
| Gharaat | A watermill in the hills that uses flowing water to grind grains |
| Stored energy | Energy kept for later use, like in a battery |
3. Important Topics
A. What Is Energy?
- Energy is what makes things move, light up, produce sound, do work and change temperature.
- Balloon rocket: air rushing out of a balloon pushes it forward, so moving air has energy.
- Rubber band guitar: plucked bands vibrate and make sound energy. Thick and thin bands make different sounds.
- Water in the Sun: water in sunlight gets warmer, because the Sun gives heat energy.
B. Sources of Energy
| Who or What | Source of Energy |
|---|---|
| Humans and animals | Food |
| Cars and scooters | Petrol and diesel |
| Cooking at home | Cooking gas, wood, coal, electricity |
| Diya | Oil |
| Fans, lights, TV | Electricity |
| Torch and toys | Batteries (stored energy) |
- Our body stores energy, and our brain uses energy even when we sleep.
- Burning wood and coal causes smoke and pollution.
C. Electricity
- It can make things move (fan), make sound (radio), give light (bulb) and make heat (iron).
- Factories use electricity to make clothes, toys, books and vehicles.
- LED bulbs give the same light using less electricity. This is energy efficiency.
Electricity safety rules:
- Don’t touch wires or plugged-in devices.
- Don’t put fingers, pens or sticks into sockets.
- Stay away from broken wires and fallen poles, and tell an adult.
- Don’t play near electric boxes or transformers.
- Never fix electrical things yourself.
D. Energy from the Sun, Wind and Water
| Source | Activity | Used For |
|---|---|---|
| Sun | Magnifying glass burns paper | Drying clothes and papad, solar panels |
| Wind | Pinwheel spins | Windmills, sailing ships |
| Flowing water | Water wheel turns | Gharaats, electricity from rivers |
- Most electricity comes from burning coal, which pollutes the air.
- Electricity from the Sun, wind and water is clean energy.
- The Sun is the main source of energy for life on Earth. It gives Earth more energy in one hour than all humans use in a whole year.
E. India’s Energy Examples
- Bhadla Solar Park in Rajasthan is one of the world’s largest solar plants.
- Cochin Airport in Kerala is the first airport fully powered by solar energy.
- Ancient Indian traders sailed to Africa, Arabia and Southeast Asia using wind.
- In cold regions, people keep cattle on the ground floor so their body heat warms the rooms above.
- Traditional houses had thick walls and small windows to stay cool in summer and warm in winter.
4. Question-Answers
Very Short Answer Questions
1. What is energy?
What makes things move, light up, make sound, do work and change temperature.
2. What is our source of energy?
Food.
3. What is the source of energy for vehicles?
Fuels like petrol and diesel.
4. What is the fuel in a diya?
Oil.
5. Which bulb saves electricity?
An LED bulb.
6. What do solar panels do?
They turn sunlight into electricity.
7. What is the main source of energy on Earth?
The Sun.
8. What are gharaats?
Watermills in hilly areas that use flowing water to grind grains.
9. Name one thing that stores energy.
A battery.
10. Which airport runs fully on solar energy?
Cochin International Airport, Kerala.
Short Answer Questions
1. Why does a balloon move when we let it go?
The air rushing out of the balloon pushes it forward. This shows that moving air has energy.
2. How does a rubber band guitar make sound?
When we pluck the rubber bands, they vibrate and produce sound. This is sound energy.
3. Why is burning coal and wood harmful?
Burning coal and wood releases smoke and harmful gases that pollute the air. This is bad for our health and the environment.
4. What is clean energy? Give examples.
Energy from natural sources that doesn’t pollute is called clean energy. Examples are solar energy, wind energy and energy from flowing water.
5. What is energy efficiency?
Using less energy to do the same work. For example, an LED bulb gives the same light as an old bulb but uses less electricity.
6. Write three rules for using electricity safely.
Don’t touch wires of plugged-in devices, never put anything into a socket, and tell an adult if you see broken wires.
Long Answer Questions
1. Explain the different sources of energy we use every day.
Food gives energy to people and animals to move, play and think. Fuels like petrol and diesel run vehicles, and cooking gas, wood and coal are used for cooking. Electricity runs fans, lights, TVs and machines. Batteries store energy for torches and toys. The Sun, wind and flowing water are natural sources that help dry clothes, sail ships, grind grain and make clean electricity.
2. Why should we use solar and wind energy instead of coal?
Burning coal pollutes the air with smoke and harmful gases, and coal will run out one day. Solar and wind energy come from nature, will never run out and don’t pollute. They help keep the air clean and the planet healthy.
Textbook Exercise Answers (Let us reflect)
1. What would happen if there was no electricity at home for a day?
There would be no fans, lights, TV or charging for phones. Food in the fridge might spoil, water pumps would stop, and studying at night would be difficult.
2. Why is it better to use solar or wind energy instead of coal?
They are clean, don’t pollute the air and will never run out, while coal causes pollution and is limited.
3. Give two examples of stored energy.
A battery in a torch, and energy stored in our body from food.
4. One thing you can do at home to save energy.
Switch off lights and fans when leaving a room.
5. List three objects that use energy and their source.
| Object | Source of Energy |
|---|---|
| Fan | Electricity |
| Scooter | Petrol |
| Gas stove | Cooking gas |
6. Which diya burns longer and why?
The diya with oil burns longer, because oil is the fuel. The wick alone burns out quickly.
7. What happens to the pinwheel in the wind?
It spins, because the wind has energy.