Changes Around Us

Objectives

To make the students aware about the various changes around us.

To make the students understand the reasons behind the changes.

To motivate students to minimize changes which adversely affect us or our environment.

Contents What is change? Types of changes. Slow and fast changes Desirable and undesirable changes Reversible and irreversible changes Periodic and non periodic changes Physical and chemical changes Conclusion

What is change?

Every day we observe changes around us. For example the change of day and night, flowering of plants, ripening of fruits, rainfall etc.

Change is the transition of any substance from one form to another.

Types of changes

Slow and fast changes Desirable and undesirable

changes Reversible and irreversible

changes Periodic and non periodic changes Physical and chemical changes

Slow Changes

Slow changes are those which take a long time to occur. For example the germination of seed to form plant, growth of child into an adult and further into an old man, rusting of iron etc.

Fast Changes

Fast changes take less time to occur or Occur

instantaneously. For example burning of paper, bursting of balloon, burning of matchstick.

Desirable Changes There are some changes which occur as

we wish. We like such changes that is why these are called desirable changes. For example formation of curd from milk, formation of manure from cow dung and dead plants.

Undesirable changes There are some

changes which do not occur as per our wishes. Such changes are called undesirable changes. For example earthquakes, excessive heat in due to rise in temperature in summers and breaking of glass.

Sometimes undesirable changes accompany desirable changes

The running of car on road is desirable but it also produces smoke, carbon dioxide and other harmful gases which pollute the environment. Hence it becomes the undesirable change.

Some changes may be desirable for one person but undesirable for others.

For example the cutting of tree may be may be desirable for one who needs wood but undesirable for others because it disturbs the balance in nature as trees produce oxygen which is necessary for all human beings on earth.

Periodic Changes Changes which occur

again and again after fixed intervals of time are known as periodic changes. For example change of day and night, occurrence of full moon, heart beat and oscillation of pendulum of clock.

Non-Periodic changesThere are some changes which do not repeat themselves at regular intervals. You can not predict when they will reoccur. For example occurrence

of earthquake, train accidents, sneezing, rusting of iron etc.

Reversible Changes If a change can be reversed then it is called reversible change. For example on cooling water to the freezing point it changes into ice and ice changes back into water on heating.

Irreversible Changes There are some changes which can not be

reversed such changes are called irreversible. For example growth of child into an adult and then from an adult to an old man.

Physical Changes Changes in which

size or shape of the object may change but the substance of which they are made of remain the same. For example formation of water vapours on heating water.

Water vapours

Chemical Changes The changes in which new substances

are formed are called chemical changes. For example rusting of iron lead to formation of iron oxide.

2Fe + O2 --------->2FeOIron Oxygen Rust

We can not get back iron or oxygen from iron

oxide. So it is a chemical change.

Conclusion

We should try to minimize changes which adversely affect the human beings or their environment.

For example: Cutting of trees, Pollution etc.

Exercise

Tell which type of change is this: Growing of a plant from a seed. Evaporation of water. Occurring of tides in the sea. Revolving of earth around the sun.

References

Text book of class 6th. Dinesh Simplified Science and

Technology (Chemistry) Google search. Yahoo search.