Introduction

Introduction

We have many things around us. All these things have certain properties such as state (solid, liquid or gas), position, shape, size, colour, temperature, composition and structure, etc. When one or more properties of a thing become different, we say that it has changed or a change has taken place in it. Changes involve different kinds of alterations in the things around us. When a change takes place, there may be a change in the state, position, shape, size, colour, temperature, composition or structure of the material of the object. Here is an example. When ice melts, it forms water. Now, we know that ice is a solid whereas water is a liquid. So, the melting of ice involves a change in sate (from solid state to liquid state). Some of the important changes observed by us in our everyday life are:

1. Formation of curd from milk
2. Cooking of food
3. Burning of fuels
4. Drying of clothes, and
5. Rusting of iron

We can go on adding more and more examples of changes to this list. Some more examples of the changes around us are: Melting of ice, Boiling of water (or Evaporation of water); Making of chapattis from flour, Burning of fire-works, Germination of seeds, Flowering of plants, Ripening of fruits, Shedding of leaves by trees, Growth of human beings and animals, Formation of day and night, Position of sun in the sky, Change in Seasons, Change in weather, and Rainfall, etc.

Some changes are beneficial to us whereas some are harmful to us. We try to ensure that the beneficial changes take place faster but the harmful changes are either stopped or made to go slow. For example, the ripening of fruits is a beneficial change. So, we try to make the ripening of fruits faster by sung artificial methods. On the other hand, the spoiling of cooked food is a harmful change, so we try to slow down this change by keeping the cooked food in a refrigerator.

The change in a material (or object) does not occur on its own. There is always a ‘cause’ which brings about a change in a material. For examples, ice does not melt to form water on its own. Ice must be given heat to melt and change into water. Thus, heat is the cause of the change of state of ice from solid to liquid. In fact there is always a ‘cause’ for a change. It is this ‘cause’ which brings about the change in a material. In some changes the ‘cause’ is very obvious but in other changes it is not so obvious.

Some of the ways of bringing about changes in materials are by applying heat, light, electricity, or force. A change can also be brought about in a material ‘by mixing another substance’ to it. For example, when water is mixed with sugar, then sugar dissolves in water to form sugar solution. Now, dissolving sugar in water is a change is a change which has been brought about by mixing another substance ‘water’ to sugar.