1. INTRODUCTION
In our daily life, we observe many changes around us. Everything in this universe undergoes a change. These changes may be observed by us at school, home, playground, garden or any other place. For example, sudden change in weather, flowering of plants, melting of ice, ripening of fruits, drying of clothes, milk changing into curd, germination of seeds, cooking of food, rusting of iron, bursting of firecrackers etc., are the common changes that occur in day-to-day life.
The changes can bring about different kinds of alterations in the things around us. Some of the alterations brought about are permanent in nature, and hence, cannot be reversed. However, some alterations are brought about in position, shape, size or state of the things. These alterations are temporary in nature, and hence, can be reversed.
Classification Of Changes
The changes taking place around us can be classified as under :
(1) Slow and fast changes.
(2) Reversible and irreversible changes.
(3) Desirable and undesirable changes.
(4) Periodic and non-periodic changes.
(5) Physical and chemical changes
2. SLOW AND FAST CHANGES
Some changes are very fast. These changes occur within seconds or minutes.
Examples: A boy blowing a balloon, bursting of a balloon, burning of a match stick, bursting of a cracker, lighting of an electric bulb, spinning of a top, etc., are examples of fast changes
Some changes take place very slowly. These changes may take hours, days, months or years to complete.
Examples:
1. Germination of a mustard seed into a seedling may take a few days. The growth of a seedling into a full fledged mustard plant may take three months or more.
2. A baby grows into an adult in over 18 years.
3. Rusting of an iron nail in damp air may take a couple of days.
4. Milk changes into curd in 6 to 8 hours.
5. The water changes into ice in a fridge in a few hours.
The change of seasons from summer to winter takes months.
3. REVERSIBLE AND IRREVERSIBLE CHANGES
A change which can be reversed is called a reversible change. In this change, the products formed can
be converted back into their original forms.
Examples
1. Water can be changed into ice by placing it in the freezing chamber of the fridge. The ice so formed can be converted back into water by placing the ice outside the fridge.
2. An electric bulb can be made to give light by passing electric current through it. The bulb returns to its original state and does not give light when the electric current is switched off.
3. A piece of steel can be converted into a magnet by rubbing with a powerful magnet. The magnet so formed can be converted back into steel by hammering it or heating it strongly.
A change which cannot be reversed is called an irreversible change. In this change, the products cannot be converted back into their original form.
Examples:
1. When a paper is burnt, it changes to ash and smoke. From ash and smoke, we cannot get back paper.
Thus, the change is irreversible.
2. A candle, on burning, forms carbon dioxide gas and water vapour. These products cannot be converted back into a candle.
3. When a sparkle is set on fire, it burns with a bright flame. However, on cooling, the products do not change back into sparkle.
4. Similarly, curdling of milk, weathering of rocks, grinding of grains, cooking of food, falling of leaves from a tree, the ageing of human beings, animals and plants are irreversible changes.
4. DESIRABLE AND UNDESIRABLE CHANGES
A change brought about by a person or the nature, which is a useful change is called a desirable change.
Examples:
1. Formation of curd from rnilk is a desirable change. It is because curd is more easily digestible as compared to milk.
2. Formation of manure from animal dung and dead leaves is a desirable change. It is because waste materials are converted into useful manure which is good for raising crops.
3. Melting of snow on the mountains in the summer is a desirable change. It is because it brings fresh supply of water to the rivers.
4. Change of weather from winter to summer is a desirable change. It is because the heat results in evaporation of water on a large scale. The water so evaporated changes to clouds and brings about rain which is good for the crops.
A change brought about by a person or the nature, such that it has harmful effects is failed an undesirable change.
Examples
1. Food turning bad in summer is an undesirable change. It is because it not only spoils food, but people can get ill white eating such food.
2. Flooding of rivers in rainy seasons is an undesirable change. It is because the floods wash away the standing crops and cover the fertile soil with sand.
3. Breaking of glassware/glass article is an undesirable change. It is because the broken glass cannot be rejoined.
4. Rusting of articles of iron is an undesirable change. It is because rusting makes the articles of iron weak.
It must be pointed out here that a change which is desirable at one i- time, may be undesirable at some other time.
For example, if wood or coal is burnt in a proper place, the heat is produced which is a desirable change.
It is because we can use the heat in cooking food or generating steam in factories. However, if a house or a factory catches fire, it also produces heat. This heat just causes destruction, and hence, is undesirable.
Sometimes while carrying out desirable changes, some undesirable changes may also take place.
The following examples will highlight the point :
1. The heat produced by the burning of petrol in the engines of cars or scooters is a desirable change. It is because it helps us to drive the cars and scooters. However, at the same time, the poisonous gases like carbon monoxide and nitric oxide are produced which are very harmful to health. This is an undesirable change.
2. In the thermal power stations, electricity is produced by producing heat energy from the burning of coal. It is a desirable change. However, burning of coal produces a lot of smoke and other poisonous gases. These gases arc harmful to health. This is an undesirable change.
Thus, to sum up, a change may be desirable for some people and undesirable for others. For example, when a farmer sprays chemicals on vegetables and fruits to kill insects, it is a desirable change for the farmer, because he gets a good crop. However, the chemicals used by the farmer may be harmful to the persons who are consuming his crop. Thus, it is an undesirable change. Similarly, cutting of forest for wood may be useful to some persons who need wood.
However, cutting of wood disturbs the balance of nature, which can cause drought, water shortage, etc. Thus, while bringing about a desirable change, care should be taken that there is minimum of undesirable changes.
5. PERIODIC AND NON-PERIODIC CHANGES
Periodic Changes
The changes which occur again and again, after fixed intervals of time, are called periodic changes.
Examples :
1. Swinging of a clock pendulum is a periodic change.
2. Phases of moon is a periodic change.
3. Change of seasons is a periodic change.
4. High and low tides at sea is a periodic change.
5. Beating of heart is a periodic change.
Non-Periodic Changes
The changes which do not repeat themselves at regular intervals of time are called non-periodic changes.
Examples:
1. Earthquakes are non-periodic changes.
2. Landslides during rainy season are non-periodic changes.
3. Falling of leaves from a tree is a non-periodic change.
4. Rusting of iron articles is a non-periodic change.
5. Sneezing, coughing, etc., are non-periodic changes.