Objects, Materials, and Grouping

There is a vast variety of objects all around us, each with different shapes, colours, and uses. This includes everything from chairs, books, and toys to water and stones. A fundamental concept in science is to organize or sort these objects into groups to better understand them.

Grouping can be done based on various criteria:

• Based on Shape: We can group all objects that are round (e.g., rubber ball, football, marble) or nearly round (e.g., apples, oranges, earthen pitcher).
• Based on Use: We can group items that are edible or items used for preparing food.
• Based on the Material They Are Made From: We can create a group of all objects made of plastic (e.g., buckets, toys, pipes). This is one of the most common ways of sorting.

---

Understanding Materials

All objects around us are made of one or more materials. A material is the matter from which an object is made. Common materials include wood, paper, glass, metal, plastics, cotton, and soil.

The relationship between objects and materials is key:

1. An object can be made from a single material (e.g., a wooden chair).
2. An object can be made from many materials (e.g., a pen made of plastics and metal).
3. A single material can be used to make many different objects (e.g., wood can be used to make a chair, table, plough, and bullock cart).

---

Examples of Objects and Their Materials

Object	Plate (Thali)	Pen	Chair	Book
Materials it is made of	Steel, Glass, Plastics	Plastics, Metal	Wood, Plastics, Metal	Paper

---

Examples of Materials and Objects Made from Them

Material	Objects made of these materials
Wood	Chair, table, plough, bullock cart and its wheels, doors
Paper	Books, notebooks, newspaper, toys, calendars, matchbox
Plastics	Buckets, lunch boxes, toys, water containers, pipes, pen
Cotton	Clothes, towels, bed sheets, dusters, wicks for lamps
Metal	Nail, hammer, plate (thali), pen, car, tractor

Properties of Materials: Appearance and Hardness

The choice of a material for making a particular object depends on its properties and the purpose for which the object is to be used. For example, a tumbler is used to hold a liquid. Therefore, it is made of materials like glass, plastic, or metal that can hold water. It would be silly to make a tumbler from cloth, as cloth cannot hold liquid. Similarly, we don't use paper-like materials for cooking vessels.

Let us explore some important properties of materials.

---

Appearance (Lustre)

Materials often look different from one another. One of the key properties related to appearance is lustre, which means shine. Some materials are shiny, while others are dull.

• Lustrous Materials: Materials that have a natural shine or lustre are called lustrous. This property is characteristic of most metals like iron, copper, aluminium, and gold.
• Non-Lustrous Materials: Materials that are dull and do not have a shine are called non-lustrous. Examples include wood, paper, cardboard, and chalk.

Sometimes, metals may lose their shine and appear dull due to the action of air and moisture on their surface. However, their lustre can be seen on a freshly cut surface or if the surface is rubbed with sandpaper.

---

Hardness

Hardness refers to how difficult it is to compress or scratch a material.

• Hard Materials: These are materials that are difficult to compress or scratch. For example, iron, stone, and wood are hard materials.
• Soft Materials: These are materials that can be easily compressed or scratched. For example, cotton, sponge, and candle are soft materials.

We can test for hardness by trying to scratch the surface of one material with another. For instance, a metal key can easily scratch a piece of chalk but cannot easily scratch a piece of stone.

Properties of Materials: Solubility

Solubility is the property of a solid, liquid, or gaseous substance (solute) to dissolve in a liquid solvent to form a homogeneous solution. For our general understanding, we often test solubility in water, as water is a universal solvent and plays a crucial role in our body's functions.

---

Solubility of Solids in Water

When we mix solid substances in water, two outcomes are possible:

• Soluble: Substances that completely disappear or dissolve in water are said to be soluble in water. Examples include salt and sugar.
• Insoluble: Substances that do not mix with water and do not disappear even after stirring for a long time are said to be insoluble in water. Examples include sand, chalk powder, and sawdust.

Substance	Disappears in water / Does not disappear
Salt	Disappears completely in water (Soluble)
Sugar	Disappears completely in water (Soluble)
Sand	Does not disappear (Insoluble)
Chalk powder	Does not disappear (Insoluble)
Sawdust	Does not disappear (Insoluble)

---

Solubility of Liquids in Water

Similar to solids, some liquids mix with water while others do not.

• Miscible Liquids: Liquids that mix completely with water are called miscible. Examples include vinegar and lemon juice.
• Immiscible Liquids: Liquids that do not mix with water and form a separate layer are called immiscible. Examples include mustard oil, coconut oil, and kerosene.

---

Solubility of Gases in Water

Some gases are also soluble in water. Water in rivers, lakes, and seas usually has small quantities of certain gases dissolved in it. For example, oxygen gas dissolved in water is crucial for the survival of aquatic plants and animals.

Properties of Materials: Floatation and Transparency

Other important properties that help us classify materials are their behaviour in water (whether they float or sink) and how they interact with light (transparency).

---

Floating and Sinking in Water

When insoluble substances are placed in water, they either float on the surface or sink to the bottom. This property is related to the density of the material compared to water.

• Objects that Float: Materials that are less dense than water will float. Examples include dried leaves, sawdust, and some plastics.
• Objects that Sink: Materials that are denser than water will sink. Examples include a stone, a metal key, and honey.

---

Transparency

Transparency is a property that describes how much light can pass through a material. Based on this, we can group materials into three categories:

1. Transparent: These are materials through which we can see clearly. They allow most of the light to pass through them. Shopkeepers often store items like biscuits and sweets in transparent containers so that buyers can easily see them.

   Examples: Glass, water, air, some plastics.

2. Opaque: These are materials through which we cannot see at all. They do not allow any light to pass through them. You cannot tell what is kept inside a closed wooden box or a metal container because they are opaque.

   Examples: Wood, cardboard, metals, stone.

3. Translucent: These are materials through which we can see, but not clearly. They allow some light to pass through in a scattered manner. An oily patch on a sheet of paper is a good example of a translucent material.

   Examples: Oiled paper, frosted glass, butter paper.

The Need for Sorting and Grouping Materials

We have learned that materials can be grouped based on similarities or differences in their properties like lustre, hardness, solubility, floatation, and transparency. But why do we need to group materials in the first place?

---

Reasons for Grouping Materials

There are two main reasons why sorting and grouping materials is useful:

1. For Convenience in Everyday Life

We often group materials and objects for our own convenience. This systematic arrangement helps us to locate things easily.

• At Home: We usually store things in a way that similar objects are placed together. For example, all clothes are kept in a cupboard, all utensils are kept in the kitchen, and all books are kept on a shelf.
• In a Shop: A grocer or shopkeeper arranges their goods in groups. For instance, all types of biscuits are kept in one section, all soaps in another, and all grains and pulses in a different section. This helps both the shopkeeper and the customers find items quickly.

---

2. For Systematic Study

Grouping materials is not just for convenience; it is a fundamental practice in science. Dividing materials into groups based on their properties allows us to:

• Study their properties in an organized manner.
• Observe and identify patterns in these properties.

By understanding these patterns, we can predict the behaviour of new materials and make informed decisions about which material is best suited for a particular purpose. This systematic study of materials is essential for science and engineering.

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer: