Educational Galaxy

Materials Around Us — EG's own notes, in simple words

Book: Curiosity (CBSE, Class 6)  |  Chapter 6  |  Medium: English

Diagram (labels are printed on the image): Materials for testing: water, salt, sand and wood. A general teaching picture about material properties.

Everyday objects made of different materials, each chosen for its properties.

Diagram (labels are printed on the image): Seeing through a material tells its group: clearly through (transparent), partly through (translucent), or not at all (opaque).

What the chapter is about

Everything around us is made of materials — paper, wood, cloth, glass, metal, plastic, clay and more. Any substance that is used to create an object is called a material. One object can be made from different materials, and one material can be used for many objects: a chair can be wood, iron, plastic or bamboo, and plastic can be a bottle, a chair or a bag.

To study so many objects, we group them. Classification is arranging objects into groups on the basis of a common property. The same set of objects can be grouped in different ways — by shape, colour, hardness, shine, or by the material itself — and friends may group them differently. What matters is stating the property used for the grouping.

Appearance is a first property. Some materials have lustre — a shiny surface, like polished metal, gold and silver. Others are dull, like wood, paper and chalk. Over time a shiny surface can lose its lustre and look dull, for example when metal gets a dull coating. Colour alone is a weak grouping property, because the same material can come in many colours.

Hardness is tested by pressing or scratching. A material that cannot be pressed or scratched easily is hard, like iron, stone and diamond. A material that can be pressed or scratched easily is soft, like sponge, cotton and eraser. Hardness is not the same as strength or weight: a heavy object can still be soft.

Seeing through a material gives three groups. Transparent materials let us see objects clearly through them: glass, clear water and air. Translucent materials let us see only partly, not clearly: butter paper and frosted glass. Opaque materials do not let us see through at all: wood, cardboard and metals. That is why shop containers are often transparent — we can see what is inside without opening them.

Solubility is tested by mixing in water. Some materials dissolve completely in water and are soluble, like salt, sugar and glucose. Others do not dissolve and are insoluble, like sand, sawdust and chalk powder. Some liquids mix with water, like vinegar, while others, like mustard oil, do not mix — they stay separate. Even some gases dissolve in water: the oxygen dissolved in water is what fish breathe.

Weight and space give two more ideas. Two objects of the same size can feel different in the hand — one heavy, one light — because their materials differ. And every material takes up space: an object has volume, the space it occupies, and mass, the amount of matter in it. Anything that has mass and occupies space is called matter. Air is matter too, even though we cannot see it: it occupies space and has mass, which is why air in a balloon takes up room and why we cannot see each other through a wooden door, while air does not block our view.

Properties decide uses. A cooking pot is metal because metal is hard and conducts heat. A raincoat is plastic because plastic does not let water through. A window is glass because glass is transparent and hard. When we choose a material, we are really choosing its properties.

What you should learn

• Define material and matter, and tell mass from volume.
• Test and name properties: lustre, hardness, transparency, solubility.
• Classify objects as transparent, translucent or opaque, with reasons.
• Tell soluble from insoluble in water, including liquids and gases that dissolve.
• Explain how properties decide the use of an object, with everyday examples.

Chart / Table: Grouping materials by properties

Table: Grouping materials by properties (NCERT-style)

Table: Choosing a material for a job

Practice set — try it yourself

1. Give two materials that are hard and two that are soft.
   Hint: Think about pressing or scratching them.
2. Why is a cooking pot made of metal and not of paper?
   Hint: Think about heat and strength.
3. Classify: glass, wood, salt, sand — by transparency and solubility.
   Hint: Test each property separately.
4. What is a translucent material? Give one example.
   Hint: Think about letting some light through, not clearly.
5. Why are raincoats made of plastic?
   Hint: Think about water passing through.

Questions with Answers

1. What is meant by the properties of a material? Give three examples.
   A property is a quality of a material that tells us how it behaves, such as hardness, lustre, solubility in water, or transparency. Properties help us choose the right material for each use.
2. Classify these materials as soluble or insoluble in water: salt, sand, sugar, chalk powder. Explain the test.
   Salt and sugar are soluble because they disappear when stirred in water. Sand and chalk powder are insoluble because they settle down and can be seen even after stirring.
3. What is the difference between transparent, translucent and opaque materials?
   Transparent materials, like clear glass, let light pass through clearly so objects behind them are seen sharply. Translucent materials, like butter paper, let only some light through so objects look blurred. Opaque materials, like wood, let no light through.
4. Why are cooking vessels made of metals like steel?
   Metals are strong, hard, and good conductors of heat, so they do not break easily and they carry heat to the food quickly. They are also easy to clean.
5. A student says a shiny plastic sheet is a metal because it is lustrous. Is she right? Why?
   No, she is not right. Lustre alone does not prove a material is a metal. Metals are also usually hard, strong and good conductors of heat, while plastic is soft, light and a poor conductor, so other tests are needed.

More NCERT-exercise questions — extra practice

1. Unscramble and match: (i) T R E M A T, (ii) U L S B E L O, (iii) T N E R P A S N A R T, (iv) E R U S T L — with (a) objects seen clearly through it, (b) occupies space and has mass, (c) shiny surface, (d) mixes completely in water.
   (i) MATTER — (b) occupies space and has mass. (ii) SOLUBLE — (d) mixes completely in water. (iii) TRANSPARENT — (a) objects seen clearly through it. (iv) LUSTRE — (c) shiny surface.
2. Why are containers in shops and at home usually transparent? Give a reason.
   So that what is inside can be seen without opening the container. Transparency saves time and avoids opening every container to check its contents.
3. State True or False, correcting the false ones: (i) Wood is translucent while glass is opaque. (ii) Aluminium foil has lustre while an eraser does not. (iii) Sugar dissolves in water whereas sawdust does not. (iv) An apple is matter because it occupies no space and has mass.
   (i) False — wood is opaque, glass is transparent. (ii) True. (iii) True. (iv) False — an apple is matter because it occupies space AND has mass.
4. Air is all around us but does not stop us seeing each other, while a wooden door does. Choose: air is ____, door is ____. (transparent/opaque)
   Air is transparent, the wooden door is opaque. That is why we see through air but not through wood.
5. Two mysterious materials X and Y: X feels rigid and does not change shape when pressed, but dissolves completely in water. Y changes shape easily when pressed and does not dissolve. Is X hard or soft? Is Y hard or soft? Justify.
   X is hard (rigid, resists pressing) and soluble. Y is soft (changes shape easily on pressing) and insoluble. Hardness is judged by pressing, solubility by mixing in water — the two tests are independent.
6. Who am I? (a) I have lustre. (b) I can be easily compressed. (c) I am hard and soluble in water. (d) You cannot see clearly through me. (e) I have mass and volume but you cannot see me.
   (a) A metal like a steel plate or gold. (b) A sponge or cotton. (c) A salt crystal (hard, soluble). (d) Butter paper — translucent. (e) Air — matter that is invisible.
7. From vinegar, honey, mustard oil, water, glucose and wheat flour: make two pairs where one dissolves in the other, and two pairs where one remains insoluble in the other.
   Soluble pairs: glucose in water; vinegar in water (they mix). Insoluble pairs: wheat flour in water (does not dissolve fully); mustard oil in water (stays separate). Honey in water dissolves, so it is not an insoluble pair.
8. Chairs are made of wood, iron, plastic, bamboo, cement and stone. Which material suits these needs best: (i) hardness, (ii) lightweight, (iii) not feeling very cold in winter, (iv) easy to clean and make look new?
   (i) Hardness: iron or stone. (ii) Lightweight: plastic or bamboo. (iii) Not cold in winter: wood or plastic (metals feel cold). (iv) Easy to clean: plastic or iron. No single material suits all four best — that is why chairs come in different materials.
9. You need containers for (i) food waste, (ii) broken glass, (iii) wastepaper. Which materials would you choose, and which properties matter?
   (i) Food waste: a washable, waterproof container such as plastic or metal, because it must not leak or rot. (ii) Broken glass: a hard, thick container that glass cannot cut through, such as a metal tin, for safety. (iii) Wastepaper: a light, dry container such as cardboard or plastic, because paper must stay dry. Properties: waterproofness, hardness/safety, and lightness.

How to use this page: Read the summary, say the Key Terms in your own words, then try the practice set without looking. Use the Questions with Answers to check yourself afterwards. Ask your teacher or parent to check your answers.