Chapter – Sorting Materials into Groups
- 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 types of materials.
- Different types of materials have different properties.
- Materials are grouped together on the basis of similarities and differences in their properties.
Properties of materials
- Materials that have such lustre 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.
- We therefore, notice the lustre, only on their freshly cut surface.
- Materials which can be compressed or scratched easily are called softwhile some other materials which are difficult to compress are called hard. For example, cotton or sponge is soft while iron is hard.
Soluble or Insoluble
- Some substances completely dissolve in water. 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 substances are insoluble in water.
- Water plays an important role in the functioning of our body because it can dissolve a large number of substances.
Objects may float or sink in water
- Some of these materials that do not mix with water, floated to the surface of water. Others sink to the bottom.
- Those 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. These materials are called opaque. Wood, cardboard and metals, are examples of opaque materials.
- Material through which objects can be seen, but not clearly, are known as translucent.
- We can therefore group materials as opaque, transparent and translucent.
- Dividing materials in groups makes it convenient to study their properties and also observe any patterns in these properties.
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