Materials Around UsClass 6 Science Notes

Materials Around Us

All things are made up of some materials, such as paper, wood, cloth, glass, metal, plastic, and clay. Any substance that is used to create an object is referred to as a material. Based on everyday observations, objects are made up of various materials.

How to Group Materials?

An object can be made from different materials, and some materials can be used to make more than one object. The method of arranging objects into groups is called classification. Objects can be classified based on common properties they share, such as shape, colour, hardness, softness, shine, dullness, or the materials they are made up of. Similarly, materials can be classified based on certain properties.

The choice of material for an object depends on its properties and the purpose for which it will be used. For example, cooking utensils cannot be made from paper-like materials because they need to withstand heat and be durable. A tumbler made of cloth cannot be used for storing water because cloth is absorbent and would not hold water. Therefore, materials required to make a tumbler should be capable of holding water.

Different materials can also be used for different parts of a single object. For instance, a pen may be made of plastic, metal, and ink, each chosen for its specific properties suitable for that part. Grouping objects and materials helps us study and observe patterns in their properties. This classification is useful in daily life, like organizing items in a kitchen or a shop.

What are the Different Properties of Materials?

Materials exhibit various properties that distinguish them from one another.

Observe and identify appearance of materials

Materials often look different. For example, freshly cut wood looks different from iron, and iron looks different from copper or aluminium. These differences in appearance are due to various properties.

Materials that typically have shiny surfaces are said to have a lustrous appearance. Such materials with lustre are usually metals. Examples of metals include iron, copper, zinc, aluminium, and gold. However, metals can lose their lustre and appear dull or non-lustrous over time due to the effect of air and moisture. This is why lustre is often most noticeable on their freshly cut surfaces.

Non-lustrous materials are those that do not have a shiny surface. Examples include paper, wood, rubber, and jute. It is important to note that not all materials that shine are metals. Some materials can be made to look shiny by polishing or coating them with thin layers of plastic, wax, or other materials. These materials may not inherently be metals.

Which materials are hard?

When you press different objects or materials, some are hard to compress, while others are easily compressed. This property is known as hardness.

Soft materials are those that can be compressed or scratched easily, such as an eraser or a sponge. Hard materials are those that are difficult to compress or scratch, like stones or iron. It is important to remember that these properties are relative. For instance, rubber is harder than a sponge but softer than iron.

Explore materials through which one can see or cannot see

Materials can be categorized based on how much light passes through them, affecting our ability to see objects through them.

Transparent materials are those through which things can be seen clearly. Examples include glass, water, air, and cellophane paper. These materials allow light to pass through them almost entirely, with minimal scattering.

Opaque materials are those through which you cannot see at all. They block light completely. Examples of opaque materials include wood, cardboard, and most metals.

Translucent materials are those through which objects can be seen, but not clearly. They scatter light as it passes through, making images appear hazy or blurry. Butter paper and frosted glass are examples of translucent materials.

What is soluble in water; what is not?

When materials are mixed with water, they behave differently. Some materials completely disappear when mixed in water. We say that these materials dissolve in water, or they are soluble in water. Examples include sugar and salt.

Other materials do not mix with water and do not disappear even after being stirred for a long time. These materials are insoluble in water. Examples include chalk powder, sand, and sawdust.

Water plays a crucial role in the functioning of our body because it can dissolve a large number of materials, which helps in various bodily processes.

Some liquids also exhibit solubility properties when mixed with water. Some liquids, like vinegar and honey, get completely mixed with water. Others, like oil, do not mix with water and form a separate layer when left undisturbed for some time. Similarly, some gases are soluble in water, while others are not. For example, oxygen gas dissolves in water, which is vital for the survival of aquatic animals and plants.

How heavy or light?

The property that determines how heavy or light an object is, is called mass. An object that is heavier has more mass, and an object that is lighter has less mass. While "weight" is often used interchangeably with mass in common language because it is determined by weighing, mass and weight are distinct concepts that you will learn more about in higher classes.

Space and volume

All objects occupy space. The space occupied by matter is called its volume. For example, when water is poured into tumblers of the same capacity, different amounts of water will occupy different levels, indicating different volumes. A tumbler half-filled with water has less volume of water than one that is almost completely filled.

You may have noticed drinking water bottles with labels like $1 \text{ L}$, $500 \text{ mL}$, or $200 \text{ mL}$. These indicate the volume of water contained in the bottles.

What is Matter?

All materials possess two fundamental properties: mass and volume.

Matter is defined as anything that occupies space and has mass. The mass of an object quantifies the amount of matter present in it. The standard units to measure mass are gram (g) and kilogram (kg). The volume is the space occupied by matter. The standard units to measure volume are litre (L) and millilitre (mL).

• The kilogram (kg) is the unit of mass in the International System of Units (SI). It is abbreviated as $\text{kg}$ (lower case 'k' and 'g', no space between them, and no full stop after the symbol). When writing mass, always leave a space between the number and the unit, e.g., $7 \text{ kg}$.
• The litre (L) is abbreviated as capital $\text{L}$ and millilitre (mL) as $\text{mL}$ (lower case 'm' and upper case 'L', no space between them). For example, $500 \text{ mL}$ of water.
• The SI unit for volume is the cubic metre, abbreviated as $\text{m}^3$. The abbreviation is written with a superscript $3$ to denote cubic metre. For example, $2 \text{ m}^3$. Always leave a space between the number and the unit.
• The conversion between litres and cubic metres is $1 \text{ m}^3 = 1000 \text{ L}$.

All materials around us can be considered examples of matter. For example, water, sand, pebbles, and a cup are all matter because they occupy space and have mass. Materials are essentially specific types of matter used in the creation or making of objects.

Grouping materials based on their similarities or differences in properties helps us to study and understand them better. This systematic classification is not new; humans have classified things throughout history, including in ancient India. Ayurveda, an Indian medical system, described 20 properties (guna) to describe all physical matter, which can also be applied to living systems, the environment, and food. These properties are grouped into ten pairs of opposites: (i) guru (heavy) $\times$ laghu (light in weight) (ii) manda (slow) $\times$ tīkṣhṇa (quick, fast) (iii) hima (cold) $\times$ uṣhṇa (hot) (iv) snigdha (unctous) $\times$ rukṣha (dry) (v) śhlakṣhaṇa (smooth) $\times$ khara (rough) (vi) sāndra (solid) $\times$ drava (liquid) (vii) mridu (soft) $\times$ kaṭhina (hard) (viii) sthira (stable) $\times$ khāla (moving, unstable) (ix) sūkṣhma (subtle, small) $\times$ sthūla (big, gross) (x) viśhada (non slimy) $\times$ picchhila (slimy)