Everything we see and use in our daily lives, from a simple pen and notebook to furniture and buildings, is made up of different substances. These substances are called materials.

Just like ancient texts mention that materials like clay and iron were used to make objects (like a crucible for melting substances), we can observe that the objects around us are created from a variety of materials such as paper, wood, cloth, glass, metal, plastic, and clay.

An object can be made from a single type of material, or it can be made from a combination of different materials (e.g., a pen made of plastic, metal, and containing ink).

Observing Objects Around Us

Identifying Materials

By looking closely at objects around us, we can identify what materials they are made from.

For example, a chair can be made of wood, plastic, or metal. A notebook is made of paper. A glass tumbler is made of glass.

This observation helps us understand that the same type of object can sometimes be made from different materials.

How To Group Materials?

Grouping Objects And Materials

We can organize or group objects based on various similarities. For example, we can group them by:

• Shape: All round objects together, all square objects together.
• Colour: All red objects together, all blue objects together.
• Texture: Objects that feel smooth together, objects that feel rough together.
• Material: Objects made of wood together, objects made of plastic together.

Similarly, we can group materials themselves based on their inherent characteristics or properties.

What Is Classification?

The process of arranging objects or materials into groups based on common properties or characteristics is called classification.

Classification helps us organize our understanding of the world around us.

Why Do We Group Materials?

Grouping materials is useful for several reasons:

• It makes it easier to study the properties of different materials.
• It helps us to organize and find things easily (e.g., keeping all similar utensils together in a kitchen, or all spices in one place in a shop).
• By classifying based on properties, we can better understand how materials behave and what they are suitable for.

Humans have classified not just non-living materials but also living organisms, rocks, and other aspects of the natural world to bring order to diverse information.

Choosing Materials For Objects

When we want to make an object, we choose a material based on two main things:

1. The properties of the material.
2. The purpose for which the object will be used.

For example, a tumbler (cup) needs to hold liquid, so it must be made from a material that does not absorb water (like cloth or paper) and is strong enough to hold the liquid. Glass, metal, or plastic are suitable materials for a tumbler, but paper or cloth would not be.

Different sports balls, though similar in function (being a ball), are made of different materials (tennis ball is rubber/felt, cricket ball is leather/cork) because they are used in different ways and need specific properties like bounce, weight, and durability for each sport.

Properties Of Materials

Materials have many different properties that we can observe and use for classification.

Appearance Of Materials (Lustre)

Materials often look different from each other. One noticeable property is their surface shine.

• Lustrous materials: These materials have a shiny appearance. Metals like iron, copper, aluminum, gold, and zinc are typically lustrous. However, the shiny surface of metals can become dull over time due to reactions with air and moisture. You can often see the true lustre on a freshly cut surface of a metal.
• Non-lustrous materials: These materials do not have a shiny surface. Examples include paper, wood, rubber, and jute.

It is important to note that not everything shiny is necessarily a metal. Some non-metallic surfaces can be made to look shiny through polishing or applying coatings.

Hardness And Softness

Another way to describe materials is by how easily they can be compressed or scratched.

• Hard materials: These are difficult to compress or scratch. Examples include stone, iron, and wood.
• Soft materials: These can be compressed or scratched easily. Examples include cotton, sponge, rubber, and chalk.

Hardness and softness are relative properties. Something considered hard might be softer than something else. For example, rubber is harder than a sponge but softer than iron.

Object	Hard/Soft	Material(s)
Brick	Hard	Baked clay
Pillow	Soft	Fabric, Filling (cotton/foam)
Stone	Hard	Rock/Mineral
Cotton ball	Soft	Cotton

Seeing Through Materials (Transparency, Opacity, Translucency)

Materials can be classified based on whether or how clearly we can see through them.

• Transparent materials: Materials through which objects can be seen clearly. Light passes through them easily. Examples: Glass, clean water, air, cellophane paper.
• Opaque materials: Materials through which you cannot see at all. Light does not pass through them. Examples: Wood, cardboard, metals, a wall.
• Translucent materials: Materials through which objects can be seen, but not clearly (the view is hazy or blurry). Some light passes through, but it is scattered. Examples: Frosted glass, butter paper, some plastics.

Based on this property, people choose materials for specific uses, like using transparent glass for windows to see outside, or opaque wood/metal for doors for privacy.

Transparent	Translucent	Opaque
Glass tumbler	Butter paper	Eraser
Window glass (clear)	Frosted glass	Wooden board

Solubility (Soluble And Insoluble In Water)

When some materials are mixed with water (or other liquids), they seem to disappear completely. This property is called solubility.

• Soluble materials: Materials that completely dissolve in water (or another liquid) are called soluble. Examples in water: Sugar, salt, glucose.
• Insoluble materials: Materials that do not mix with or dissolve in water, even after stirring, are called insoluble. They may settle down or float. Examples in water: Sand, chalk powder, sawdust.

Water is often called a 'universal solvent' because it can dissolve a large number of substances. This property is important for biological processes, including in our bodies and for life in water bodies (like oxygen dissolving in water for aquatic organisms).

Liquids can also be soluble or insoluble in water. For example, vinegar mixes completely with water (soluble liquid), while oil does not and forms a separate layer (insoluble liquid).

Gases can also dissolve in water, like oxygen which is vital for aquatic life.

Material	Observation
Sugar	Disappears in water (dissolves)
Salt	Disappears in water (dissolves)
Chalk powder	Does not disappear in water (remains as solid particles)
Sand	Does not disappear in water (settles down)
Sawdust	Does not disappear in water (may float or suspend)

Mass (Heavy Or Light)

We can describe objects or materials as being 'heavy' or 'light'. This refers to a fundamental property called mass.

• The mass of an object is a measure of the quantity of matter it contains.
• Something that is heavier has more mass, and something that is lighter has less mass.

We can compare the masses of different materials using a balance. For example, a cup filled with pebbles is likely heavier (has more mass) than an identical cup filled with water, which might be heavier than a cup filled with sand (depending on the type of sand and pebble size).

The standard SI unit for mass is the kilogram (kg). A smaller unit is the gram (g), where $1 \text{ kg} = 1000 \text{ g}$.

Extra Information: In common language, 'weight' is often used when we mean mass, as mass is determined by weighing. Weight is actually a force (due to gravity), and you will learn more about the difference between mass and weight in higher classes.

Volume And Space

All objects and materials take up space. The amount of space that a substance or object occupies is called its volume.

When bags are kept on seats, you cannot sit there because the bags occupy the space of the seats.

If two identical tumblers have different levels of water, it means the *amount* of water in them is different. The water in the tumbler with the lower level occupies less space than the water in the tumbler with the higher level, so it has a smaller volume.

The SI unit for volume is the cubic metre (m$^3$). For measuring volumes of liquids, units like litre (L) and millilitre (mL) are commonly used. $1 \text{ L} = 1000 \text{ mL}$, and $1 \text{ m}^3 = 1000 \text{ L}$.

Labels on bottles like '500 mL' indicate the volume of the liquid inside.

What Is Matter?

Definition Of Matter

Based on the properties of mass and volume, we can define a fundamental concept in science.

Matter is anything that occupies space (has volume) and has mass.

Units Of Mass And Volume

• Mass is measured in units like grams (g) and kilograms (kg). $1 \text{ kg} = 1000 \text{ g}$.
• Volume is measured in units like millilitres (mL), litres (L), and cubic metres (m$^3$). $1 \text{ L} = 1000 \text{ mL}$, $1 \text{ m}^3 = 1000 \text{ L}$.

Materials As Matter

All the materials we have discussed – wood, plastic, metal, glass, water, sand, even air – are examples of matter because they all take up space and have mass.

Materials can be thought of as specific types of matter used to create objects.

Classification Of Matter

Just as we classify objects and materials based on their properties, matter itself can be classified based on its properties (like being solid, liquid, or gas; magnetic or non-magnetic; transparent or opaque; soluble or insoluble, etc.).

This system of classifying matter based on properties helps scientists and people in daily life understand and utilize different substances effectively.

Extra Information: Ancient Indian systems like Ayurveda also had detailed classifications of substances based on their observable properties, similar to modern scientific classification.

Think it over: The invention and widespread use of plastic is a good example of how materials with specific properties (lightweight, durable, waterproof) can be very useful, but can also pose significant challenges (like pollution) if not managed properly. This highlights the need to consider the full impact of materials we use.

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