Science in Everyday Life — Class 5 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 5 Science, Unit 4. Changes around us, the scientists who shaped our lives, and managing our waste. Taught in August and September.
1. Changes all around us
Science has helped us find solutions to many problems, and it has shaped our daily life. The world we live in is not the same as before — it changes every day, in fact every hour.
Look closely at those changes and they fall into two kinds.
2. Reversible changes
A reversible change can be undone. The substance can be brought back to what it was.
Melt ice and you get water; freeze the water and you get ice again. Boil water into steam, cool the steam, and water returns.
Melting, freezing and boiling are reversible changes.
3. Irreversible changes
Changes which cannot be reversed are called irreversible changes.
Burn a piece of paper and it turns to ash. The ash can never become paper again.
Irreversible changes are also known as permanent changes. Burning, cooking and the rusting of iron are all irreversible.
The test is simple: ask whether you can get the original substance back. Cooked rice cannot become raw rice. A rusted nail cannot become shiny iron by itself.
4. Scientists who shaped our lives
| Scientist | Field | Contribution |
|---|---|---|
| Sir C.V. Raman | Physics | Scattering of light |
| Dr. A.P.J. Abdul Kalam | Aeronautical Engineering | Missile development |
| Dr. M.S. Swaminathan | Genetics | Green Revolution |
| Srinivasa Ramanujan | Mathematics | Number theory |
| Venkatraman Ramakrishnan | Biology | Structure of the ribosome |
5. Sir C.V. Raman and the blue sky
Sir C.V. Raman worked in physics on the scattering of light.
His work answers a question every child asks. Why does the sky appear blue? Sunlight is a mixture of colours. As it passes through the atmosphere, the tiny particles of air scatter the blue light far more than the other colours, and that scattered blue reaches our eyes from every part of the sky.
So the blue appearance of the sky is due to the scattering of light — not reflection, and not refraction.
6. Dr. A.P.J. Abdul Kalam
Avul Pakir Jainulabdeen Abdul Kalam (1931–2015) was an aeronautical scientist, known as the Missile Man of India.
- Born on 15 October 1931 in Rameswaram, Tamil Nadu.
- Took his B.Sc. from St. Joseph's College, Tiruchirappalli, in 1954.
- Took his degree in Aeronautical Engineering from the Madras Institute of Technology in 1960.
He went on to lead India's missile development programme, and later became the President of India.
7. Wastes
Waste is any substance which is discarded after primary use. It is worthless, defective and of no use — unwanted and undesirable material.
Waste comes from several places.
Household wastes include vegetable peels, food scraps, packaging, plastic and glass.
Wastes from school are the ones you produce yourself: papers, pens and their parts, blades, chocolate wrappers and plastic items. If they are not collected and disposed of properly, the school environment becomes polluted.
8. Why waste must be disposed of properly
With so much waste lying everywhere, a proper waste management system is needed.
To control pollution. Water pollution, air pollution and soil pollution can all be avoided by handling waste correctly.
To protect health. Rotting waste breeds flies, mosquitoes and rats, and these spread disease.
To keep surroundings clean. A clean school and a clean street are pleasanter and safer for everyone.
To recover what is useful. Much of what we throw away — paper, glass, metal, plastic — can be recycled rather than buried.
The first step is always the same: separate the waste where it is produced, keeping wet kitchen waste apart from dry recyclable waste.
9. Worked examples
Example 1. The blue appearance of the sky is due to which property of light?
Solution: Scattering.
Example 2. Who is known as the Missile Man of India?
Solution: Dr. A.P.J. Abdul Kalam.
Example 3. Give an example of a reversible change.
Solution: Melting ice into water, which can be frozen back into ice.
Example 4. Circle the odd one: melting, freezing, boiling, cooking.
Solution: Cooking, because it is irreversible while the other three are reversible.
Example 5. Circle the odd one: boiling, burning, cooking, rusting of iron.
Solution: Boiling, because it is reversible while the other three are irreversible.
Example 6. What is another name for irreversible changes?
Solution: Permanent changes.
Example 7. Who contributed to the Green Revolution, and in what field?
Solution: Dr. M.S. Swaminathan, in genetics.
10. Practice
- What is a reversible change? Give one example.
- What is an irreversible change? Give two examples.
- Why does the sky appear blue?
- In which field did Sir C.V. Raman work?
- Where and when was Dr. A.P.J. Abdul Kalam born?
- From which college did Abdul Kalam take his B.Sc.?
- What is waste?
- Name four waste items commonly found in a school.
- Give two reasons why waste needs proper management.
- Circle the odd one: vegetables, flowers, fruits, chemicals.
11. Answers
- A change that can be undone, such as melting ice into water and freezing it again.
- A change that cannot be undone, such as burning paper or cooking food.
- Because air particles scatter the blue part of sunlight far more than the other colours.
- Physics, on the scattering of light.
- In Rameswaram, Tamil Nadu, on 15 October 1931.
- St. Joseph's College, Tiruchirappalli, in 1954.
- Any substance which is discarded after primary use, being unwanted and of no further value.
- Papers, pen parts, blades and chocolate wrappers (also plastic items).
- To control water, air and soil pollution, and to protect health by not breeding disease carriers.
- Chemicals, because the other three are biodegradable while chemicals are not.
12. Summary
- Reversible changes can be undone: melting, freezing and boiling.
- Irreversible or permanent changes cannot: burning, cooking and rusting of iron.
- Burnt paper becomes ash and can never be paper again.
- Sir C.V. Raman worked on the scattering of light, which explains the blue sky.
- Dr. A.P.J. Abdul Kalam, the Missile Man of India, was born in Rameswaram on 15 October 1931.
- Dr. M.S. Swaminathan led the Green Revolution and Srinivasa Ramanujan worked in mathematics.
- Waste is any substance discarded after primary use.
- School waste includes paper, pen parts, blades and wrappers.
- Waste management controls pollution, protects health, keeps surroundings clean and recovers materials.
- Separating waste where it is produced is always the first step.
