Do you know how many kinds of things are around us?

As you look around your room, you can see your pencils, boxes, clothes, etc. These are made up of wood, plastic or metal. They also come in different shapes, colours and sizes.
You can sort different objects using the material of which they are made. That material can also make other different things.
For example, paper can be used to make boxes, books and calendars. A chair, tables, and pencils are made of wood. Cotton can be used to make shirts, bags, towels etc.
Yet, clothes can be made from cotton or silk, but not wood. Similarly, chairs cannot be made using cotton. This is because using other materials would not be as useful.
Some properties of a material help us decide how and where to use them; properties like:
Appearance:
Iron looks different from wood and glass. Paper looks different from chalk and aluminium.
Metals show a shiny surface when cut in middle. This is called the lustre of metals. You can even see if you rub metal with sandpaper.

Old metals do not have shine on them because of the action of air and moisture.

Hardness:

You must have noticed that pressing or scratching materials like wood, metal and glass is very difficult. These are hard materials.
However, it is easier to press and scratch cotton and sponge as they are soft.

Soluble and insoluble materials:

Materials which are in powder form can be identified based on whether they disappear/dissolve in water.
If they dissolve in water, they are soluble materials. Those that cannot dissolve are insoluble materials.
Here are a few examples. You can add more to the list.

Material	Soluble	Insoluble
Gas	Oxygen
Liquid	Mango Lemon	Vegetable oilpetrol
Powder form	SaltSugar	ChalkClay

Floating and sinking objects:
Some objects go from the surface of the water surface to the bottom. They are sinking objects. Others remain on the surface and are called floating objects. For example, leaf and wood float on the surface of the water but stone and spoon sink in it.

Transparency:
If you have to hide chocolate from your naughty cousin, where will you hide it? Will you choose a metal box or a glass container?
Why do you choose the metal box?
This is because you can easily see through a glass container but it is not possible to see through a metal box. The materials that let you see through them are called transparent materials. And those that do not let you see through them are called opaque materials.

There are materials that let you see through them but not very clearly. These are called translucent materials.
Sorting materials by grouping and separating them helps us identify the correct material for a particular use. We learn a lot by identifying similarities and differences among different materials. This is in the same way that a shopkeeper separates different candies into different jars so that he can find them easily when you go to buy them.

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