Grade 6 Ch 6 Materials Around Us

  

        Grade 6 Chapter 6: Materials Around Us 

 1. Introduction to Materials and Objects

• Material: Any substance used to create an object. Examples include paper, wood, cloth, glass, metal, plastic, and clay.
• Object: A thing made from one or more materials. Objects around us vary in shape, colour, and texture.
• Key Principles:
• An object can be made from a single material or a combination of different materials (e.g., a pen made of plastic, metal, and ink).
• A single material can be used to make many different objects (e.g., wood can be used to make chairs, tables, and doors).
• The choice of material for an object depends on the material’s properties and the object’s intended purpose. For example, a tumbler must be made of a material that can hold water, making materials like cloth or paper unsuitable.

2. Grouping and Classification of Materials

• Classification: The method of arranging objects or materials into groups based on common properties, similarities, or differences.
• Purpose of Classification: Grouping materials and objects helps in studying them systematically and observing patterns in their properties. This is a common practice in various settings, such as kitchens, grocery stores, and chemist shops, to organize items efficiently.
• Bases for Classification: Objects and materials can be grouped based on various properties, including:
• Shape
• Color
• Hardness or softness
• Lustre (shine) or dullness
• The material they are made of

3. Key Properties of Materials

3.1 Appearance

• Lustrous: Materials that have a shiny surface, often referred to as lustre. Metals like iron, copper, gold, and aluminum are typically lustrous. Some metals may lose their lustre due to exposure to air and moisture, but the shine is visible on freshly cut surfaces.
• Non-Lustrous: Materials that do not have a shiny surface. Examples include paper, wood, rubber, and jute.
• Important Note: Not all shiny materials are metals. Some surfaces are made shiny by polishing or coating them with other materials like plastic or wax.

3.2 Hardness

• Hard Materials: Materials that are difficult to compress or scratch. Examples include stone, iron, and wood.
• Soft Materials: Materials that can be easily compressed or scratched. Examples include erasers, candles, and chalk.
• Relativity of Hardness: Hardness is a relative property. For instance, rubber is harder than a sponge but softer than iron.

3.3 Transparency

• Transparent: Materials through which objects can be seen clearly. Light passes through them completely. Examples include glass, water, air, and cellophane paper.
• Opaque: Materials through which objects cannot be seen at all. They block light completely. Examples include wood, cardboard, and metals.
• Translucent: Materials through which objects can be seen, but not clearly. They allow some light to pass through in a scattered manner. Examples include butter paper and frosted glass.

3.4 Solubility in Water

• Soluble: Materials that completely dissolve or disappear when mixed in water. Examples include sugar, salt, and oxygen gas. Water’s ability to dissolve many substances is crucial for bodily functions.
• Insoluble: Materials that do not mix with water and do not disappear, even after stirring. Examples include sand, chalk powder, sawdust, and oil. Some liquids form a separate layer, and some solids settle at the bottom.

3.5 Mass (Heaviness/Lightness)

• Mass: A property that quantifies the amount of matter in an object. Objects that are heavier have more mass, while lighter objects have less mass.
• Measurement: Mass is measured using a balance. In common language, “weight” is often used interchangeably with mass. The standard units are the gram (g) and kilogram (kg).

3.6 Volume (Space Occupied)

• Volume: The amount of space occupied by an object or substance.
• Concept: Every object occupies space. For example, a bag on a seat occupies the space, preventing someone from sitting there. The amount of water in a container represents its volume.
• Measurement: The units used to measure volume include litre (L), millilitre (mL), and the SI unit, cubic metre (m³).

4. The Concept of Matter

• Definition: Anything that occupies space (has volume) and has mass is called matter.
• Universal Properties: Mass and volume are the two fundamental properties possessed by all materials.
• Examples: All materials we encounter, including solids (sand, pebbles), liquids (water), and gases (air), are forms of matter.

5. Historical and Cultural Context

• Ancient Pottery: The earliest pottery in the Indian subcontinent dates back 7,000 to 8,000 years. The Sindhu-Sarasvatī (Harappan) Civilization (2600–1900 BCE) developed sophisticated techniques for making terracotta (baked clay) pottery, which was used for cooking and storage.
• Ayurveda Classification: The ancient Indian medical system of Ayurveda uses a system of 20 properties (guṇa), arranged in ten opposite pairs, to describe all physical matter, living systems, and food. These pairs include heavy/light, cold/hot, soft/hard, and smooth/rough.

 

Let Us Enhance Our Learning (pages 119-121)

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

Answer: Yes, food items can be sorted like this:

• Pulses (moong dal, chana dal, urad dal, etc.) in one group
• Cereals (rice, wheat flour, maize flour, etc.) in another
• Spices (turmeric, cumin, pepper, etc.) in one section
• Oils and ghee together
• Jams and squashes in another section

Question 2. Unscramble the letters (Column I) and match with their properties (Column II).

Answer:

Column I	Column II
(i) MATTER	(b) Occupies space and has mass.
(ii) SOLUBLE	(d) Mixes completely in water.
(iii) TRANSPARENT	(a) Objects can be seen clearly through it.
(iv) LUSTRE	(c) Shiny surface.

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

Answer: Containers used for storing materials at shops and homes are usually transparent so that the contents inside can be easily seen. This helps in quickly identifying the materials without opening the containers.

Question 4. State whether the statements given below are True [T] or False [F], Correct the False statements).
(i) Wood is translucent while glass is opaque.

Answer: False. Wood is opaque while 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 a matter because it occupies space and has mass.

Question 5. We see chairs made up of various materials, such as wood, iron, plastic, bamboo, cement, and stones. Following are some desirable properties of materials which can be used to make chairs. Which materials used to make chairs fulfill these properties the most?

Answer:  (i) Hardness – Iron, cement, and stones are very hard and do not bend easily.
(ii) Lightweight – Plastic and bamboo are light, so they are easy to move.
(iii) Does not feel cold in winters – Wood and bamboo feel warmer and are more comfortable.
(iv) Easy to clean and stays new – Plastic, iron, cement, and stones can be cleaned easily and look new for a long time.

Question 6. You need to have containers for collection of (i) food waste, (ii) broken glass and (iii) wastepaper. Which materials will you choose for containers of these types of waste? What properties of materials do you need to think of?

Answer: We can use plastic containers for all three types of waste.

• For food waste, the container should be leak-proof and should not react with food.
• For broken glass, the container should be strong and hard so that glass pieces do not cut through.
• For wastepaper, the container should be light but strong enough to hold papers.
  Using different colored containers helps to separate biodegradable, hazardous, and recyclable waste.

Question 7. Air is all around us but does not hinder u‘s from seeing each other. Whereas, if a wooden door comes in between, we cannot see each other. It is because air is ________ and ________ the wooden door is ______
Choose the most appropriate option:
(i) transparent, opaque
(ii) translucent, transparent

(iii) opaque, translucent

(iv) transparent, translucent

Answer: (i) transparent, opaque

Question 8. Imagine you have two mysterious materials, X and Y. When you try to press material X, it feels rigid and does not change its shape easily. On the other hand, material Y easily changes its shapk when you press it. Now, when you mix both materials in water, only material X dissolves completely, while material Y remains unchanged. What can materials X and Y be? Can you identify whether material X is hard or soft? What about material Y? Justify your answer.

Answer: X can be sugar crystal and Y can be rubber block.

The material X is hard.

The material Y is soft.

Question 9. (i) Who am I? Identify me on the basis of the given properties.
(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.

(ii) Make your own Who am I?’
Answer:
(i) (a) steel
(b) rubber
(c) sugar
(d) cardboard or plywood
(e) air

(ii) (a) You can see clearly through me
(b) I am soft
(c) I am non-lustrous
(d) I am liquid and insoluble in water
(e) I cannot be compressed easily.