NCERT Revision Notes for Class 5 EVS Chapter 7: Energy — How Things Work – Free PDF Download

Chapter 7 of Class 5 EVS (Our Wondrous World), Energy — How Things Work, explores what energy is, the many sources it comes from, and how it powers everything from a moving fan to a growing plant, while also looking at the difference between renewable and non-renewable sources.

Key Concepts

What Is Energy?

Energy is the ability to do work or cause change – it is what makes things move, heat up, light up, or grow. Without energy, machines would not run, muscles could not move, and even simple actions like boiling water or switching on a bulb would be impossible.

Sources of Energy

Energy comes from many different sources:

• The Sun: the ultimate source of most energy on Earth, powering photosynthesis in plants, and directly usable through solar panels and solar cookers.
• Fossil fuels: coal, petroleum (oil), and natural gas, formed over millions of years from the remains of ancient plants and animals; widely used for electricity generation, vehicles, and industry.
• Wind: moving air that can turn windmills and wind turbines to generate electricity.
• Water: flowing or falling water used in hydroelectric power plants to generate electricity.
• Food: provides chemical energy that our bodies convert into the energy needed to move, think, and grow.
• Biogas: produced from decomposing organic waste like cattle dung or kitchen waste, used as a fuel for cooking or lighting.

Renewable vs Non-Renewable Energy

Renewable sources of energy – sunlight, wind, and flowing water – are naturally replenished and do not run out with use. Non-renewable sources – coal, petroleum, and natural gas – take millions of years to form and are being used up much faster than nature can replace them, meaning their supplies are limited.

Forms of Energy

Energy exists and changes between different forms: light energy (from the sun or a bulb), heat energy (from fire or the sun), electrical energy (that powers appliances), mechanical energy (of moving objects), and chemical energy (stored in fuel or food). A single device often converts energy from one form to another – for example, an electric bulb converts electrical energy into light and heat energy.

How Machines Use Energy

Simple and complex machines all rely on some source of energy to work – a bicycle uses the rider’s muscular (chemical) energy, a car uses chemical energy stored in fuel, and a fan or mixer uses electrical energy. Understanding this helps explain why a machine stops working when its energy source (charge, fuel, or electricity) runs out.

Saving Energy

Since non-renewable energy sources are limited and their use can also cause pollution, saving energy matters. Simple habits include switching off lights and fans when not needed, using natural light during the day, walking or cycling for short distances instead of using fuel-powered vehicles, and using energy-efficient appliances.

Quick Recap

• Energy is the ability to do work or cause change, and it comes from sources like the sun, fossil fuels, wind, water, food, and biogas.
• Renewable sources (sun, wind, water) are naturally replenished, while non-renewable sources (coal, petroleum, natural gas) are limited and take millions of years to form.
• Energy exists in different forms – light, heat, electrical, mechanical, and chemical – and often changes from one form to another as machines work.
• Every machine, from a bicycle to a mixer, needs some source of energy to function.
• Saving energy through simple daily habits helps conserve limited resources and reduce pollution.

Common Mistakes to Avoid

• Thinking electricity is a source of energy on its own – electricity is generated from other sources, like coal, water, or wind, and is better understood as a form or carrier of energy.
• Confusing renewable with “unlimited and free of any impact” – renewable sources are naturally replenished, but setting up and using them (like large dams or wind farms) can still affect the environment.
• Believing fossil fuels can be quickly replaced once used up – they take millions of years to form naturally, so they are considered non-renewable on a human timescale.
• Overlooking food as a genuine source of energy for the human body, focusing only on machines and electricity.
• Assuming energy is only about electricity and fuel, and forgetting forms like light, heat, and mechanical energy that appear constantly in daily life.

Home Practice Tips

• Walk through your home and list five devices, noting whether each uses electrical, chemical (battery/fuel), or another form of energy.
• Identify one renewable and one non-renewable energy source used in your own home or neighbourhood.
• Practice switching off lights, fans, or appliances when leaving a room for a week, and discuss the effect with family.
• Discuss with family how their household got electricity, gas, or fuel before certain modern conveniences became common.
• Watch sunlight move across a room during the day and discuss how solar panels or solar cookers make direct use of that same sunlight.

Frequently Asked Questions

Q1. What is energy, and why do we need it?
Energy is the ability to do work or cause change; we need it for everything from moving our bodies and running machines to producing light and heat.

Q2. What is the difference between renewable and non-renewable energy sources?
Renewable sources, like sunlight, wind, and flowing water, are naturally replenished and do not run out with use, while non-renewable sources, like coal, petroleum, and natural gas, take millions of years to form and are limited in supply.

Q3. Why is the sun called the ultimate source of most energy on Earth?
Because sunlight powers photosynthesis in plants, which forms the base of most food chains, and it is also directly used through solar panels and solar cookers, making it central to both natural and human-made energy use.

Q4. Is electricity itself a source of energy?
Not exactly – electricity is generated from other energy sources, such as coal, flowing water, or wind, so it is more accurate to think of it as a very useful form of energy rather than an original source.

Q5. Why is it important to save energy in daily life?
Because non-renewable sources like coal and petroleum are limited and take millions of years to replace, and using less energy also tends to reduce pollution, so simple habits like switching off unused appliances help conserve resources for the future.

Full walkthrough: Chapter 7 Solutions · Extra Questions.

Written by Satish

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