Introduction to the Topic

Welcome to NCERT Explained: Class VI Science, Chapter 4 - Sorting Materials into Groups! Have you ever wondered why we don't store water in a paper bag, or why cooking utensils are made of metals rather than cloth? Around us, we see a vast variety of objects such as a chair, a toy, a book, a stone, and much more. All these objects are made of one or more materials. These materials could be paper, glass, plastic, wood, cotton, metals, or mud. Sorting materials into groups based on their properties is an essential skill that helps us organize our world, study objects systematically, and understand their everyday uses. In this chapter, we will explore how and why we classify different objects.

Key Concepts Explained

1. What is an Object Made Of?

An object can be made of different types of materials. For example, a plate can be made of steel, glass, plastic, or even clay. Sometimes, a single object could be made of many materials—like a bicycle, which is made of iron, rubber, plastic, and leather. To understand why a specific material is chosen for an object, we must first look at its properties.

2. Properties of Materials

Different materials have different properties. Two objects made of the same material can look entirely different, but their core properties remain consistent. Let us look at the main properties discussed in the NCERT textbook:

  • Appearance: Materials usually look different from each other. Wood looks very different from iron, and iron looks different from aluminium or copper. However, some common features may exist between iron and copper, but they differ from wood. Materials that have a shiny appearance are often called metals. Examples include iron, copper, aluminium, and gold. Some metals lose their shine and appear dull because of the action of air and moisture on them.
  • Hardness: When you press different materials with your hands, some may be hard to compress, while others can be easily compressed. Materials that can be compressed or scratched easily are called soft materials, whereas some other materials which are difficult to press are called hard materials. For example, cotton or sponge is soft, while an iron nail is hard.
  • Soluble or Insoluble: Have you ever mixed sugar in water? What happens to it? Some substances completely disappear or dissolve in water; we say that these substances are soluble in water. Other substances do not mix with water and do not disappear even after we stir for a long time; these are called insoluble substances. For example, salt and sugar are soluble in water, while sand and chalk powder are insoluble.
  • Transparency: The substances or materials through which things can be seen are called transparent. Glass, water, air, and some plastics are examples of transparent materials. On the other hand, there are some materials through which you are not able to see at all. These materials are called opaque. Wood, cardboard, and metals are examples of opaque materials. Materials through which objects can be seen, but not clearly, are known as translucent (e.g., oiled paper or frosted glass).

Summary & Key Takeaways

Sorting objects into groups makes it easier to study their properties and observe any patterns. Here are the quick takeaways from Class VI Science Chapter 4:

  • Objects around us are made up of a large variety of materials.
  • A given material could be used to make a large number of objects. It is also possible that an object could be made of a single material or of many different materials.
  • Based on properties like appearance, hardness, solubility, transparency, and density, materials are grouped together.
  • Materials are grouped for convenience and to study their properties easily.
  • Transparent objects let light pass through clearly, opaque objects block light completely, and translucent objects allow partial light passage.