Materials Around Us

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A–3, B–5, C–1, D–2, E–4

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Hint: Any substance used to create an object — e.g., paper, wood (also cloth, glass, metal, plastic, clay).

Hint: The method of arranging objects into groups; on the basis of a common property.

Hint: Cloth cannot hold water — the material for a tumbler must be capable of holding water.

Hint: Glass or steel — they can hold water (are rigid and non-leaky).

Hint: The properties of the material and the purpose for which the object is to be used.

Hint: Lustrous — shiny surface (iron); Non-lustrous — no shine (paper/wood/rubber/jute).

Hint: Air and moisture dull older surfaces of metals.

Hint: Hard — difficult to compress/scratch (stone); Soft — easily compressed/scratched (eraser/candle).

Hint: Rubber is harder than sponge but softer than iron.

Hint: Transparent — things seen clearly (glass, water, air); Opaque — cannot see through (wood, metals, cardboard).

Hint: Materials through which objects can be seen but not clearly — butter paper, frosted glass.

Hint: Frosted glass is translucent, so only a hazy image is seen; she could not be seen clearly.

Hint: Soluble — sugar, salt; Insoluble — sand, sawdust (also chalk powder).

Hint: Water can dissolve a large number of materials.

Hint: Mix six teaspoons of sugar and half a teaspoon of common salt in one litre of boiled and cooled water.

Hint: Mass is the measure of how heavy/light an object is; the heavier object has more mass.

Hint: 7 kg (no 's', space between number and unit); 500 mL (m lowercase, L uppercase).

Hint: The space occupied by matter; common units — litre (L) and millilitre (mL).

Hint: Anything that occupies space and has mass.

Hint: Through 20 properties (guna) — ten pairs of opposites such as guru/laghu (heavy/light), hima/ushna (cold/hot), mridu/kathina (soft/hard).

Introduction: Containers used for storing materials are often made of transparent materials so that their contents can be identified easily.
Key Points:
1. Easy identification — Transparent containers allow us to see what is stored inside without opening them.
2. Checking quantity — We can observe how much material is left and decide when to refill it.
3. Saves time and effort — There is no need to open every container to find a particular item.
Conclusion: Transparency in storage containers makes identification and usage convenient in daily life.

Introduction: Materials can be classified based on how much we can see through them into three types.
Key Points:
1. Transparent materials — Objects can be seen clearly through them; examples are glass and water.
2. Translucent materials — Objects can be seen but not clearly through them; examples are butter paper and frosted glass.
3. Opaque materials — Objects cannot be seen at all through them; examples are wood and cardboard.
Conclusion: The degree to which light passes through a material determines whether it is transparent, translucent or opaque.

Introduction: In a game of hide and seek, the children chose hiding spots made of different types of materials.
Key Points:
1. Ghulan behind a wall — The wall is opaque, so he could not be seen at all.
2. Sheeta behind a tree — The tree trunk is opaque, completely blocking the view.
3. Sara behind frosted glass door — The frosted glass is translucent, giving a hazy view; her brother watching through a glass window could see clearly as glass is transparent.
Conclusion: The activity demonstrates how transparent, translucent and opaque materials affect visibility.

Introduction: Different materials behave differently when mixed with water, depending on whether they are soluble or insoluble.
Key Points:
1. Sugar and salt — These disappear completely in water after stirring, so they are soluble in water.
2. Chalk powder, sand and sawdust — These do not disappear even after stirring for a long time, so they are insoluble in water.
3. Observation method — Five tumblers were two-thirds filled with water, one material was added to each, stirred well and observed.
Conclusion: Some materials dissolve in water while others do not, which helps us classify them as soluble or insoluble.

Introduction: The chapter states that oxygen gas dissolves in water, and this is vital for aquatic life.
Key Points:
1. Evidence from aquatic life — Fish and other aquatic animals and plants survive in water, which shows that oxygen is dissolved in it.
2. Survival of aquatic organisms — Without dissolved oxygen, aquatic animals and plants would not be able to survive.
3. Solubility of gases — Some gases like oxygen are soluble in water, while others are not.
Conclusion: Dissolved oxygen in water is essential for the survival of aquatic animals and plants.

Introduction: Balls of the same size but made of different materials are used for different sports because of their varying properties.
Key Points:
1. Different bounce heights — Tennis, cricket and hand exercise balls of the same size bounce to different heights when dropped.
2. Material-specific properties — Each sport requires specific properties like hardness, bounce and texture from the ball.
3. Purpose-based selection — The material is chosen based on the properties needed for a particular sport.
Conclusion: The choice of material for sports balls depends on the specific requirements of each sport.

Introduction: Madam Vidya used two identical glass tumblers with different amounts of water to explain the concept of volume.
Key Points:
1. Different water levels — One tumbler was half-filled while the other was almost completely filled with water.
2. Same capacity, different volume — Both tumblers had the same capacity, but the amount or volume of water differed.
3. Definition of volume — The space occupied by water represents its volume; more water means greater volume.
Conclusion: Volume is the space occupied by matter, and it varies depending on the quantity of the substance.

Introduction: The SI unit of mass is kilogram (kg) and the SI unit of volume is cubic metre (m³).
Key Points:
1. Mass unit rules — Kilogram is written as kg in lowercase with no space between k and g, no plural 's', and a space between the number and unit (e.g., 7 kg).
2. Volume unit rules — Cubic metre is written as m³ with a superscript 3; 1 m³ = 1000 L; always leave a space between number and unit.
3. Litre rules — Litre is abbreviated as capital L and millilitre as mL, with no space between m and L in mL.
Conclusion: Correct usage of symbols ensures uniformity and clarity in scientific measurements of mass and volume.

Introduction: The chapter introduces mass as a property of matter and distinguishes it from the common use of the word weight.
Key Points:
1. Mass — Mass measures how heavy or light an object is; a heavier object has more mass.
2. Weight in common language — The word 'weight' is commonly used for mass, as it is determined by weighing.
3. Detailed relation in higher classes — The exact relationship between mass and weight is explained in higher classes.
Conclusion: Mass quantifies the amount of matter in an object, while weight is its everyday equivalent used in common language.

Introduction: Matter is anything that occupies space and has mass, and materials are specific types of matter used to make objects.
Key Points:
1. Matter examples — Water, sand and pebbles are all matter because they occupy space and have mass.
2. Materials in objects — When these substances are used to make objects like pots or cups, they are called materials.
3. Variety of materials — Objects are made from a variety of materials such as paper, wood, cloth, glass, metal, plastic and clay.
Conclusion: Materials are types of matter selected and used in the creation or making of various objects.

Introduction: The Sindhu-Sarasvati Civilisation developed advanced pottery techniques over thousands of years.
Key Points:
1. Wheel-turned pottery — From about 4000 BCE, they developed wheel-turned pottery production, pigmentation and decorative painting.
2. Harappan sophistication — During the Harappan Civilisation (2600–1900 BCE), pots had bright red surfaces with black geometric designs and animal motifs.
3. Clay processing — Clay was carefully selected, cleaned, sieved, kneaded, wheel-turned and baked in kilns to produce terracotta.
Conclusion: The Harappan Civilisation achieved great sophistication in pottery through advanced techniques and careful clay processing.

Introduction: The chapter describes two important terms related to pottery: slips and terracotta.
Key Points:
1. Slips — Slips are protective or decorative coats of multiple colours applied to the surface of pottery.
2. Terracotta — Terracotta is the baked clay produced when clay is baked in kilns during pottery making.
3. Use in pottery — Slips enhanced appearance and protection, while terracotta formed the durable body of the pots.
Conclusion: Slips and terracotta were key elements in the pottery techniques of ancient Indian civilisations.

Introduction: Wood is a suitable material for making a chair, especially in winter, due to its specific properties.
Key Points:
1. Hardness and strength — Wood is hard and strong enough to support the weight of a person sitting on it.
2. Lightweight — Wood is relatively lightweight, making the chair easy to move and handle.
3. Does not feel very cold — Wood does not feel very cold in winter, unlike iron or cement, making it comfortable to sit on.
Conclusion: Wood's hardness, lightness and low thermal conductivity make it ideal for chairs used in winter.

Introduction: Classification of non-living materials, like that of the living world, helps us study and understand them better.
Key Points:
1. Grouping by properties — Materials are grouped based on similarities or differences in their properties.
2. Observing patterns — Classification helps us observe patterns in the properties of materials, making study easier.
3. Choosing materials — It becomes easier to select the right material for a specific purpose when they are classified.
Conclusion: Classifying non-living materials helps us study, understand and choose materials more effectively.

Introduction: Ayurveda describes ten pairs of opposite properties called guna that are used to describe all physical matter.
Key Points:
1. Guru/Laghu — Guru means heavy and laghu means light in weight.
2. Hima/Ushna — Hima means cold and ushna means hot.
3. Mridu/Kathina — Mridu means soft and kathina means hard.
Conclusion: Ayurveda's system of opposite property pairs provides a framework for describing all physical matter.

Hint: (a) They disappeared after a while; (b) They are soluble in water; (c) Sand and sawdust are insoluble — they would not mix or disappear even after long stirring.

Hint: (a) Frosted glass — translucent; plain glass — transparent; (b) Glass is transparent, so things can be seen clearly through it; (c) No — wood is opaque, so nothing can be seen through it.

Hint: (a) Oral Rehydration Solution — used to treat dehydration due to diarrhoea or other illnesses; (b) Six teaspoons of sugar and half a teaspoon of common salt in one litre of boiled and cooled water.

Hint: (a) Yes, both have the same capacity; (b) The amount of water poured in each was different; (c) Volume is the space occupied by matter/water — units litre (L) and millilitre (mL), e.g., 500 mL marked on bottles.

Hint: (a) Candle, chalk (and wood relatively); (b) Stone, iron, aluminium; (c) Materials that can be compressed or scratched easily are soft; those difficult to compress/scratch are hard — relative, e.g., rubber is harder than sponge but softer than iron.

Hint: (a) 'kgs' — no 's' with unit symbols; 'ml' — should be mL with lowercase m and capital L; (b) 7 kg and 500 mL; (c) Kilogram (kg) and cubic metre (m³).

Hint: (a) Copper wire, aluminium foil, brass, steel; (b) Lustrous — usually metals; (c) Air and moisture act on metals making them dull/non-lustrous, so lustre is often seen only on freshly cut surfaces.

Hint: (a) X is hard, Y is soft; (b) X is soluble, Y insoluble; (c) X could be sugar/salt (hard, dissolves), Y could be wax/sawdust piece (soft, does not dissolve) — any reasonable hard-soluble and soft-insoluble examples.

Hint: (a) Ten pairs of opposite properties; (b) guru/laghu (heavy/light), hima/ushna (cold/hot) or others; (c) All living systems (plants, animals, humans), the environment and also food.

Hint: (a) The volume/net quantity of water in the bottles; (b) Even a small change in volume causes a noticeable change in level in a narrow bottle; (c) Cubic metre (m³); 1 m³ = 1000 L.

Introduction: Materials are grouped or classified based on various properties that help us study and use them effectively.
Key Points:
1. Appearance (lustre) — Lustrous materials have shiny surfaces, like iron and copper; non-lustrous materials like paper and jute do not shine.
2. Feel (hardness) — Hard materials are difficult to compress or scratch, like stone and iron; soft materials are easily compressed, like an eraser and sponge.
3. Transparency — Transparent materials like glass and water allow clear vision; opaque materials like wood and cardboard block vision completely.
4. Solubility in water — Soluble materials like sugar and salt disappear in water; insoluble materials like sand and sawdust do not dissolve.
5. Mass and volume — All matter possesses mass (measured in kg or g) and volume (measured in L or mL), which are universal properties of materials.
Conclusion: These five properties — appearance, hardness, transparency, solubility and mass/volume — are commonly used to classify materials.

Introduction: Classification is the method of arranging objects or materials into groups based on common properties.
Key Points:
1. Definition — Classification is the method of arranging objects into groups based on a common property they share.
2. Kitchen classification — In kitchens, similar utensils are placed together, and grocers keep spices in one corner and pulses and grains in another.
3. Chemist shop classification — In chemist shops, medicines are arranged systematically so they can be located quickly.
4. Advantage — easy locating — Classification makes it easier to find and locate items when needed.
5. Advantage — study and patterns — Grouping helps us study materials and observe patterns in their properties.
Conclusion: Classification brings order and efficiency to both daily life and scientific study by grouping materials logically.

Introduction: Pottery in the Indian subcontinent has a long and rich history spanning thousands of years.
Key Points:
1. Earliest pottery — The earliest pottery dates back 7,000–8,000 years at Lahuradewa (Ganga plains) and Mehrgarh (Baluchistan).
2. Sindhu-Sarasvati developments — From about 4000 BCE, wheel-turned pottery, pigmentation, slips of multiple colours and decorative painting were developed.
3. Harappan sophistication — During the Harappan Civilisation (2600–1900 BCE), pots had bright red surfaces with black designs showing geometric patterns and animals.
4. Clay processing — Clay was selected, cleaned, sieved, kneaded, wheel-turned and baked in kilns to produce terracotta.
5. Uses and exhibits — Pots were used for cooking and storage of grains, oil and ghee; large storage jars are exhibited at the National Museum, New Delhi.
Conclusion: The history of pottery in India reflects a continuous evolution from simple beginnings to sophisticated Harappan techniques.

Introduction: Lustre is the shiny appearance shown by certain materials, especially metals, when light falls on them.
Key Points:
1. Lustrous materials — Materials with shiny surfaces are lustrous; these are usually metals like iron, copper, zinc, aluminium and gold.
2. Dull appearance of metals — Air and moisture can make metals lose their lustre and look dull, so lustre is often visible only on freshly cut surfaces.
3. Non-lustrous materials — Materials like paper, wood, rubber and jute do not have shiny surfaces and are called non-lustrous.
4. Polishing and coating — Some non-metals are made shiny by polishing or coating them with plastic, wax or other materials.
5. All that glitters is not gold — Since non-metals can also be made to shine, not everything that glitters is a metal or gold.
Conclusion: Lustre is a property associated mainly with metals, but surface treatments can make non-metals appear shiny too.

Introduction: Materials can be classified as transparent, translucent or opaque based on how much we can see through them.
Key Points:
1. Transparent materials — Through these, objects can be seen clearly; examples include glass, water, air and cellophane paper.
2. Translucent materials — Objects can be seen but not clearly; examples are butter paper and frosted glass.
3. Opaque materials — Objects cannot be seen at all; examples are wood, cardboard and metals.
4. Hide-and-seek — opaque hiding spots — Ghulan hid behind a wall and Sheeta behind a big tree, both opaque materials that completely blocked the view.
5. Hide-and-seek — translucent and transparent — Sara hid behind a frosted glass door (translucent), while her brother could watch everything through a glass window (transparent) but could not see through a wooden window (opaque).
Conclusion: The hide-and-seek activity practically demonstrates the differences between transparent, translucent and opaque materials.

Introduction: Materials that dissolve in water are called soluble, while those that do not dissolve are called insoluble.
Key Points:
1. Soluble materials — These disappear when mixed in water; examples are sugar and salt.
2. Insoluble materials — These do not disappear even after stirring; examples are chalk powder, sand and sawdust.
3. Five-tumbler activity — Five tumblers two-thirds filled with water were each given one material; after stirring, sugar and salt dissolved while chalk powder, sand and sawdust did not.
4. Water as a solvent — Water dissolves a large number of materials, making it important for the functioning of our body; some liquids mix completely with water while others like oil form a separate layer.
5. Gases in water — Some gases like oxygen dissolve in water and are vital for the survival of aquatic animals and plants.
Conclusion: Water is an excellent solvent that dissolves many solids, liquids and gases, making it essential for life.

Introduction: Matter is anything that occupies space and has mass, and it can be identified using two key properties.
Key Points:
1. Definition of matter — Anything that occupies space and has mass is called matter; for example, water, sand, pebbles and cups are all matter.
2. Mass — Mass quantifies the amount of matter in an object and is measured in grams (g) and kilograms (kg).
3. Volume — Volume is the space occupied by matter and is measured in litres (L) and millilitres (mL); the SI unit is cubic metre (m³), where 1 m³ = 1000 L.
4. Rules for mass symbols — Kilogram is written as kg in lowercase, with no space between k and g, no plural 's', and a space between the number and unit (e.g., 7 kg, not 7 kgs).
5. Rules for volume symbols — Litre is capital L, millilitre is mL with no space between m and L; m³ is written with a superscript 3 and a space before it (e.g., 2 m³, 500 mL).
Conclusion: Mass and volume are the two universal properties of matter, and their units must be written following specific rules for accuracy.

Introduction: The choice of material for making an object depends on the properties of the material and the purpose of the object.
Key Points:
1. Tumbler — A tumbler must be made of a material that can hold water; cloth cannot be used as it allows water to pass through.
2. Pen — A pen may be made of different materials like plastic, metal and ink, with each part serving a different function.
3. Sports balls — same size, different materials — Tennis, cricket and hand exercise balls of the same size are made of different materials.
4. Bounce differences — When dropped from the same height, these balls bounce to different heights due to their different materials.
5. Specific material for specific use — Each sport requires specific properties like bounce, hardness and texture, so specific materials are chosen for specific sports.
Conclusion: Material selection is guided by matching the properties of the material to the intended purpose of the object.

Introduction: The difference in how air, a wooden door and frosted glass affect our vision is explained by the property of transparency.
Key Points:
1. Air is transparent — Air allows light to pass through freely, so we can see each other clearly through it without any hindrance.
2. Wooden door is opaque — A wooden door completely blocks light and vision, preventing us from seeing through it at all.
3. Frosted glass is translucent — Frosted glass allows only a hazy view, so objects behind it can be seen but not clearly.
4. Classification basis — Materials are classified as transparent, translucent or opaque based on how much we can see through them.
5. Practical importance — This classification helps us choose materials for windows, doors and partitions according to the need for visibility or privacy.
Conclusion: The transparency property explains why air does not block vision while a wooden door does, with frosted glass being intermediate.

Introduction: Plastic is a widely used material whose properties make it both useful and a cause for concern.
Key Points:
1. Mouldable — Plastic can be moulded into many shapes, making it useful for making countless objects like bottles, pens and containers.
2. Lightweight — Plastic is light in weight, which makes plastic objects easy to carry and handle.
3. Durable — Plastic is durable and long-lasting, adding to its widespread use in everyday products.
4. Versatile uses — Plastic is used for countless objects in homes, shops and industries due to its favourable properties, making it a boon.
5. Environmental concerns — Most plastic objects are used and discarded, raising concerns about waste accumulation and pollution — hence the question of whether it is a bane.
Conclusion: Plastic is a boon due to its useful properties but becomes a bane when its waste causes pollution, requiring responsible use and disposal.