Matter and Materials — Class 4 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 4 Science, Unit 2. Classifying materials by their properties, how objects behave with light, and reflection. Taught in June and July.
1. Everything is matter
Everything in the universe is matter. The desk, the air, the water in your bottle, your own body — all of it is matter.
Matter is made into materials, and materials are chosen for a job because of their properties. You can measure, see or feel a property. Most materials have more than one.
2. Hard and soft
Materials that cannot easily be compressed, cut, bent or scratched are called hard materials. Iron, stone and glass are hard.
Materials that give way easily are soft. Cotton, sponge and clay are soft.
This is why a hammer head is iron and a pillow is cotton. Swap them and neither would work.
3. Shiny and dull
Materials that reflect light well are shiny. Examples: stainless steel, gold and diamond.
Materials that do not reflect light well are dull. Examples: a candle, paper and a jute bag.
4. Rough and smooth, flexible and rigid
A rough surface feels uneven to the touch, like a brick or sandpaper. A smooth surface feels even, like glass or a polished floor.
A flexible material can be bent without breaking — a rubber band, a cycle tube, an electric wire. A rigid material holds its shape and snaps rather than bends — a wooden board, a brick.
5. Waterproof materials
Materials that do not allow water to pass through are waterproof. A raincoat is waterproof, and so is the aluminium foil on a strip of tablets.
That foil is doing a real job: it keeps medicine dry so it does not spoil.
6. How objects behave with light
Hold different objects up to a light and you will find they fall into three groups.
| Group | What happens to light | Can you see through it? | Examples |
|---|---|---|---|
| Transparent | Light passes through completely | Yes, clearly | Glass, clean water, air |
| Translucent | Some light passes through | Not clearly | Butter paper, frosted glass, oil-soaked paper |
| Opaque | No light passes through | No | Wood, stone, metals |
The window of a bus is transparent, which is why you can watch the road go by.
Think about it. Why are the walls of a house built of brick, which is opaque, rather than glass, which is transparent? Because walls are there to give shelter, privacy and strength. Glass walls would let everyone see in, and would break easily.
7. Reflection of light
We see the world because of light. Light reaches us either from the Sun or from other sources such as an electric lamp or a bulb. Objects that give off light are called light sources.
When you look into a mirror you see your own face. What you are seeing is a reflection — light bouncing off your face, striking the mirror, and coming back to your eyes.
A smooth, shiny surface reflects light neatly, which is why mirrors are polished. A rough surface scatters light in all directions, so it gives no clear image.
Mirrors can reflect sound waves too. In the Second World War, large curved mirrors of concrete were used to catch and focus the sound of approaching enemy aircraft, before radar was invented.
8. The three states of matter
Matter comes in three states, and the difference is in how tightly the particles are packed.
| State | Particles | Shape | Volume |
|---|---|---|---|
| Solid | Tightly packed | Fixed | Fixed |
| Liquid | Close but able to move | Takes the shape of the container | Fixed |
| Gas | Far apart | Fills any space available | Not fixed |
9. Changing from one state to another
| Change | From, to | Everyday example |
|---|---|---|
| Melting | Solid to liquid | Ice becomes water |
| Freezing | Liquid to solid | Water becomes ice |
| Evaporation | Liquid to gas | Wet clothes dry |
| Condensation | Gas to liquid | Water drops form on a cold bottle |
These changes are reversible. Melt ice and you get water; freeze it again and you get ice back. The substance itself has not changed, only its state.
A common misunderstanding. Evaporation does not need boiling. It happens at all temperatures, just faster when it is hot. That is why clothes on a line dry even on a cold day.
Another one. Melting is not the same as dissolving. Melting means heating a solid until it turns into liquid — the substance is still the same substance. Dissolving means a solid spreading out inside a liquid, as sugar does in water.
10. Soluble and insoluble
A material that dissolves in water is soluble: salt, sugar, washing powder, lemon juice. The result is a clear solution.
A material that does not dissolve is insoluble: sand, chalk powder, oil, plastic, metal. It floats or settles at the bottom.
Never taste an unknown liquid to identify it. Many clear liquids look exactly like water but are not — vinegar, alcohol, glycerine and some acids are all colourless.
11. Worked examples
Example 1. Find the odd one out: glass bottle, exam pad, paper plate, wooden board.
Solution: Glass bottle — it is transparent, while the other three are opaque.
Example 2. Classify: air, rock, aluminium foil, mirror, oil-soaked paper.
Solution: Air is transparent. Rock, aluminium foil and mirror are opaque. Oil-soaked paper is translucent.
Example 3. When can you say a material is waterproof?
Solution: When it does not allow water to pass through it, as a raincoat does not.
Example 4. What is a light source? Give two examples.
Solution: An object that gives off light. The Sun and an electric bulb.
Example 5. Find the odd one out: stone, rubber band, cycle tube, electric wire.
Solution: Stone — it is rigid, while the other three are flexible.
Example 6. Why does a rough wall not act as a mirror?
Solution: A rough surface scatters light in all directions instead of reflecting it neatly, so no clear image forms.
12. Practice
- What is matter?
- Name two shiny materials and two dull materials.
- Which materials are called hard?
- Give one example of a waterproof material.
- What is the difference between transparent and opaque materials?
- Define reflection.
- Name the change of state from liquid to gas.
- Is sand soluble or insoluble in water?
- Find the odd one out: umbrella, sponge, raincoat, jerkin.
- Why are house walls made of brick rather than glass?
13. Answers
- Everything in the universe is matter — anything that occupies space.
- Shiny: stainless steel, gold. Dull: paper, candle.
- Those that cannot easily be compressed, cut, bent or scratched.
- A raincoat, or the aluminium foil on a tablet strip.
- Transparent materials let light pass through so you can see clearly; opaque materials let none through.
- Light bouncing back from a surface, as from a mirror.
- Evaporation.
- Insoluble — it settles at the bottom.
- Sponge, because it soaks up water while the others are waterproof.
- Brick is opaque and strong, giving shelter and privacy; glass would be see-through and would break easily.
14. Summary
- Everything in the universe is matter, and materials are chosen for their properties.
- Hard materials resist compressing, cutting, bending and scratching; soft ones give way.
- Shiny materials reflect light well (steel, gold, diamond); dull ones do not (paper, candle).
- Waterproof materials do not let water through, such as a raincoat.
- Transparent lets light through clearly, translucent partly, opaque not at all.
- Light comes from sources such as the Sun and bulbs; reflection is light bouncing back.
- Solids have fixed shape and volume, liquids take the container's shape, gases fill any space.
- Melting, freezing, evaporation and condensation are reversible changes of state.
- Evaporation happens at all temperatures, not only when boiling.
- Soluble materials dissolve in water; insoluble ones do not.
