Heat

Objects around us:

All objects around us are made of one or more materials. These materials may be glass, metal, plastics, wood, cotton, paper, mud or soil. All the objects have different shapes, colours and uses.

An object is made of a single material or many materials.One material could be used for making many different objects.

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.

1. Appearance:

Materials usually look different from each other. At the same time, there may be some similarities between materials.

Lustre:

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.

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.

2. Soluble or insoluble:

Some substances which completely disappear or dissolve in water are soluble in water. Other substances which do not mix with water and do not disappear even after we stir for a long time are insoluble in water. Water plays an important role in the functioning of our body because it can dissolve a large number of substances.

Some liquids are soluble in water while others are not soluble in water. Vinegar is soluble in water while oils are insoluble in water. Some gases are soluble in water whereas others are not. Water, usually, has small quantities of some gases dissolved in it. For example, oxygen gas dissolved in water is very important for the survival of animals and plants that live in water.

3. Float or sink:

Some substances float on the surface of water while others sink at the bottom of the container of water.

4. Transparency:

Those substances or materials, through which things can be seen, are called transparent substances or transparent materials. Glass, water, air and some plastics are examples of transparent materials.

Some materials through which we are not able to see are called opaque materials. Wood, cardboard and metals, are examples of opaque materials.

The materials through which objects can be seen, but not clearly, are known as translucent materials. Examples are the oily patch on paper when we test food Items for presence of fats.

Why do we need to group materials?

In everyday life, we often group materials for our convenience. At home, we usually store things in such a manner that similar objects are placed together. Such an arrangement helps us to locate them easily. Dividing materials in groups makes it convenient to study their properties and also observe any patterns in these properties.