2. 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.
3. Types of changes
Slow and fast changes
Desirable and undesirable changes
Reversible and irreversible changes
Periodic and non periodic changes
Physical and chemical changes
4. 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.
5. Fast Changes
Fast changes take
less time to occur or
Occur instantaneously.
For example burning
of paper, bursting of
balloon, burning of
matchstick.
6. 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.
7. 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.
8. 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.
9. 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.
10. 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.
11. Non-Periodic changes
There 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.
12. 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.
13. 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.
14. 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
15. 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 --------->2FeO
Iron Oxygen Rust
We can not get back iron or oxygen from iron
oxide. So it is a chemical change.
16. Conclusion
We should try to minimize changes
which adversely affect the human
beings or their environment.
For example: Cutting of trees, Pollution
etc.
17. 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.
