CHAPTER 2 SORTING MATERIALS INTO GROUPS
Objects around us
Take a look around. You are surrounded by so many objects of different kind. Chairs, tables, pens, paper, water, trees, windows, etc. are just a few of the variety of the objects that we see every day. There are so many objects with different shapes, colours and material.
Properties of materials
There are a number of properties associated with the materials. Some of them are as follows:
What do you think helps us distinguish between different materials? We tell the difference by looking at them, don’t we? Materials look different from each other. Wood looks different from paper and paper looks different from metal. However, materials may look same if they are in the same category. For e.g. Aluminium and iron look similar because they’re both metals. Have you noticed how metals have a shiny appearance? You know what that’s called? It’s called ‘lustre’. Lustre is the property of metals due to which they appear to shine.
The materials that do not get compressed easily are called hard materials. For e.g. Wood, metal, etc. This property is called hardness. The materials which, on the other hand, get compressed easily are called soft materials. For e.g. Cotton, rubber, etc.
Have you noticed how salt dissolves in water? You see, if a substance dissolves in a liquid, it is said to be soluble in that liquid. However, if the substance does not dissolve in a liquid, even after stirring, it is said to be insoluble in that liquid. This property of a substance to dissolve in a liquid is called solubility.
4. Floating or sinking
Some materials do not mix with a liquid and either float to the surface or sink to the bottom. For e.g. Oil floats on the surface of water but a piece of metal sinks to the bottom.
There are some materials, like glass, that you can completely see through. Such materials are said to be transparent. The materials, like wood, that you cannot see through at all are called opaque materials. Apart from these, the materials that you can see through, but not very clearly are called translucent materials.
Advantages of sorting materials into groups