Chapter 6: Materials Around Us

 Chapter 6: Materials Around Us

1. Materials Around Us

• Everything around us is made up of materials such as paper, wood, cloth, glass, metal, plastic and clay.
• A material is any substance used to make an object.
• One object may be made from one or more materials.
• The same material can be used to make different objects.     

Examples:

- Notebook → paper

- Tumbler → glass/plastic/metal

- Pen → plastic, metal and ink

2. Classification of Materials:- Classification means arranging objects or materials into groups based on their common properties.

Materials can be grouped according to:

- Colour

- Shape

- Hardness

- Softness

- Lustre

- Appearance

- Transparency

- Solubility

- Other properties     

Why do we classify materials? Classification helps us:

• Organise objects.
• Compare materials.
• Study their properties.
• Choose suitable materials for particular uses.

3. Properties of Materials

A. Lustrous and Non-lustrous

Lustrous

Materials having a shiny surface are called lustrous.

Examples:

Iron, copper, zinc, aluminium and gold.

Non-lustrous

Materials that do not have a shiny surface are called non-lustrous.

Examples:

Paper, wood, rubber and jute.

Important: Not every shiny material is a metal. Some materials can be made shiny by polishing or coating.   

B. Hard and Soft

Hard materials

Materials that are difficult to compress or scratch are called hard.

Examples: Stone, iron.

Soft materials

Materials that can be compressed or scratched easily are called soft.

Examples: Sponge, eraser.

Remember: Hardness is relative. For example, rubber is harder than sponge but softer than iron.    

4. Transparent, Translucent and Opaque Materials

Transparent:- Materials through which objects can be seen clearly.

Examples: Glass, clean water, air and cellophane paper.

Translucent:- Materials through which objects can be seen, but not clearly.

Examples: Frosted glass and butter paper.

Opaque:- Materials through which we cannot see.

Examples: Wood, cardboard and metals.     

Easy way to remember

Type                 How much can we see?                             Example

• Transparent         Clearly                                                     Clear glass
• Translucent         Partly/unclearly                                     Butter paper
• Opaque                 Cannot see through                                     Wood

5. Soluble and Insoluble Materials:- When a material is mixed with water:

Soluble:- A material that dissolves completely in water is called soluble.

Examples: Sugar, salt.

Insoluble:- A material that does not dissolve in water is called insoluble.

Examples: Sand, sawdust, chalk powder.     

Important: Not everything disappears when put in water.

Gases in water:- Some gases can also dissolve in water. For example, oxygen dissolves in water, which is important for aquatic plants and animals.     

6. Mass – How Heavy or Light?:- The property by which we compare how heavy or light an object is, is related to its mass.

• An object with more mass is generally heavier.
• An object with less mass is generally lighter.
• Mass is measured using a balance.
• SI unit of mass = kilogram (kg).
• Another common unit = gram (g).    

Correct notation:

7 kg, not 7 kgs.

7. Space and Volume

Objects occupy space.

Volume:- The space occupied by matter is called its volume.

Common units:

- Litre (L)

- Millilitre (mL)

SI unit of volume:

- Cubic metre (m³)

Relation:

1 m³ = 1000 L

Examples:

- Water bottle → 500 mL

- Large container → several litres     

8. What is Matter?:-Anything that occupies space and has mass is called matter.

Matter has two important properties:

1. Mass – tells us the quantity of matter.

2. Volume – tells us the space occupied by matter.

Examples of matter:

- Water

- Air

- Sand

- Pebbles

- A cup     

Important units

Property Unit

Mass kilogram (kg), gram (g)

Volume litre (L), millilitre (mL)

SI unit of volume cubic metre (m³)

9. Materials and Their Uses:-We choose a material according to:

- Its properties

- The purpose for which the object is to be used.

For example:

- A tumbler should be made from a material capable of holding water.

- Cooking utensils should be made from suitable materials that can withstand their intended use.

- Different parts of an object may be made from different materials.     

10. Materials in Daily Life:-The same function can sometimes be performed by objects made from different materials.

For example, chairs can be made from:

- Wood

- Iron

- Plastic

- Bamboo

- Cement

- Stone

The choice depends on properties such as hardness, weight, comfort and ease of cleaning.     

11. Ancient Indian Classification of Properties:- The chapter also mentions that Ayurveda used a system of classifying physical matter through 20 properties arranged in 10 opposite pairs. Examples include:

- Heavy ↔ Light

- Slow ↔ Fast

- Cold ↔ Hot

- Oily ↔ Dry

- Smooth ↔ Rough

- Solid ↔ Liquid

- Soft ↔ Hard

- Stable ↔ Moving/unstable

- Small/subtle ↔ Big/gross

- Non-slimy ↔ Slimy

Let Us Enhance Our Learning – Answers

1. Visit your kitchen and observe how your parents have organised various edibles. Can you suggest a better sorting method?

Answer:- A better sorting method is to arrange edibles into separate groups according to their type and use, for example:

Grains: Rice, wheat, flour

Pulses: Dal, chickpeas, kidney beans

Spices: Turmeric, chilli, cumin

Edible oils: Mustard oil, sunflower oil

Dry fruits: Almonds, cashews, raisins

Sweet items: Sugar, jaggery

Perishable food: Fruits, vegetables and dairy products

This arrangement makes it easier to find and store food items.

2. Unscramble the letters and match them with their properties.

Column I

Unscrambled word

Correct match

(i) T R E M A T

MATTER

(b) Occupies space and has mass

(ii) U L S B E L O

SOLUBLE

(d) Mixes completely in water

(iii) T N E R P A S N A R T

TRANSPARENT

(a) Objects can be seen clearly through it

(iv) E R U S T L

LUSTRE

(c) Shiny surface

Answer:

(i) – (b)

(ii) – (d)

(iii) – (a)

(iv) – (c)

3. The containers which are used to store materials in shops and at home are usually transparent. Give your reasons for this.

Answer:- Transparent containers allow us to see the materials stored inside them clearly without opening the containers. This makes it easy to identify the contents and check their quantity.

4. State whether the statements are True or False. Correct the false statements.

(i) Wood is translucent while glass is opaque.

Answer: False.

Wood is generally opaque, while clear glass is transparent.

(ii) Aluminium foil has lustre while an eraser does not.

Answer: True.

(iii) Sugar dissolves in water whereas sawdust does not.

Answer: True.

(iv) An apple is a matter because it occupies no space and has mass.

Answer: False.

An apple is matter because it occupies space and has mass.

5. We see chairs made up of various materials. Which materials fulfil the following properties the most?

(i) Hardness

Answer: Wood, iron, bamboo, cement and stone can provide hardness. Wood or bamboo can be suitable for many chairs because they are hard and stable.

(ii) Lightweight

Answer: Plastic is generally a suitable choice because it is lightweight and easy to move.

(iii) Does not feel very cold during winters

Answer: Wood or bamboo is more suitable because they generally do not feel as cold as metals.

(iv) Can be cleaned regularly and made to look new

Answer: Plastic or metal can be suitable because their surfaces can generally be cleaned easily.

Conclusion: The choice depends on the particular property required and the purpose of the chair.

6. You need containers for collection of food waste, broken glass and wastepaper. Which materials will you choose?

Answer: Type of waste

Suitable container material

Important properties

Food waste

Plastic or metal

Strong, easy to clean, preferably leak-resistant

Broken glass

Strong metal or thick plastic

Hard, strong and resistant to breaking

Wastepaper

Cardboard or plastic

Lightweight and easy to handle

The choice of material should depend on hardness, strength, durability, weight, cleanliness and suitability for the waste being collected.

7. Air is all around us but does not hinder us from seeing each other. A wooden door prevents us from seeing each other. Choose the correct option.

Answer: (i) transparent, opaque

Explanation:

Air is transparent, while a wooden door is opaque.

8. Two mysterious materials X and Y

Material X is rigid and dissolves completely in water.

Material Y changes its shape easily and does not dissolve in water.

Answer:- X could be sugar or salt. It is hard/rigid in the sense described and dissolves in water.

Y could be sawdust. It does not dissolve in water and can be relatively easily changed or compressed.

Therefore:

X → hard and soluble

Y → soft and insoluble

The classification is based on the two properties given: hardness/softness and solubility/insolubility.

9. Who am I?

(a) I have lustre.

Answer: Metal, such as aluminium or copper.

(b) I can be easily compressed.

Answer: Sponge.

(c) I am hard and soluble in water.

Answer: Salt.

(d) You cannot see clearly through me.

Answer: Translucent material, such as frosted glass.

(e) I have mass and volume but you cannot see me.

Answer: Air.

(ii) Make your own “Who am I?”

Example:

I am transparent, I allow light to pass through me, and objects can be seen clearly through me. Who am I?

Answer: Clear glass.

10. Make pairs of soluble and insoluble materials.

Given materials: vinegar, honey, mustard oil, water, glucose and wheat flour.

Soluble pairs:

Vinegar + water

Glucose + water

Insoluble pairs:

Mustard oil + water

Wheat flour + water

Note: These pairs are based on whether one material mixes/dissolves in the other as described in the chapter.