NCERT 6TH CLASS SCIENCE CHAPTER SORTING MATERIALS INTO GROUPS
OBJECTS AROUND US
There is such a vast variety of objects everywhere. We see around us, a chair, a bullock cart, a cycle, cooking utensils, books, clothes, toys, water, stones and many other objects. All these objects have different shapes, colours and uses.
All objects around us are made of one or more materials. These materials may be glass, metal, plastics, wood, cotton, paper, mud or soil.
Properties of Materials :
We choose a material to make an object depending on its properties, and the purpose for which the object is to be used.
Some properties of materials are
(i) Appearance : Materials usually look different from each other. Wood looks very different from iron. Iron appears different from copper or aluminium. At the same time, there may be some similarities between iron, copper and aluminium that are not there in wood.
Some materials have lustre. These are usually metals. Iron, copper, aluminium and gold are examples of metals. Some metals often lose their shine and appear dull, because of the action of air and moisture on them.
Activity : To show that certain materials have lustre Material required : • Small pieces of (i) paper (ii) cardboard • a thin piece of wood • a small strip of plastic • thin wires of copper, aluminium and iron. Heavy scissors or a metal cutter • sand paper. Method:
(a) Cut each of the materials with heavy scissors or metal cutter. Carefully observe the cut surface of each material. You will notice that in case of paper card board, wood plastic, etc., the cut surface is not shining. However, in case of thin wires of copper, aluminium and Iron, the cut surface is shining.
(b) Rub each of the material with sand paper. Carefully observe the sand papered surface of the material. You will notice that in case of paper cardboard, plastiC and wool, the sand papered surface is not shining. However, in case of thin wires of copper, aluminium and iron, the sand papered surface is shining.
(ii) Hardness : When we press different materials with our hands, some of them may be hard to compress while others can be easily compressed. We can easily scratch some materials, while some cannot be scratched so easily. Materials which can be compressed or scratched easily are called soft while some other materials which are difficult to compress are called hard. For example, cotton or sponge is soft while Iron is hard.