In our previous session we learnt about the availability of water in
various forms also we saw the various uses of water.
moving ahead,
in this session we shall see Where does the water in the atmosphere
come from?
How is water available for our various uses in a
continuous manner?
Lets go step by step.
STEP 1-EVAPORATION
Friends, do you know how the wet clothes which we hang on the rope dry
up?
Where does all water from the clothes vanish?
Water does not actually disappear but because of the suns heat, it
changes from one form to another i.e water which is in the liquid state
changes to gaseous state.
In the very similar manner water continuously disperse during the day
from the various waterbodies like rivers, streams, ocean, lakes etc to
form water vapour.
And so the process where water changes from its
liquid state to gaseous state is called as EVAPORATION.
Every second 16 million tones of water eva[poartes from the surface of the earth.
But Evaporation is not limited to these waterbodies itself.Even the
plants and animals contribute to some amount of water vapour in the air.
You might be wondering how?
Plants and animals when they respire release some amount of vapour in the
air like If we keep a glass pane and exhale air on it..you will find the
surface moisture laden this is because of respiration.
When plant release
water in the form of vapours through small openings in the leaves we call
this process TRANSPIRATION.
The two process in combination called EVAPO-TRANSPIRATION contributes to
the total amount of moisture in the air.
Now lets move to the next step..what happens to the water vapor in the
STEP 2-CONDENSATION
These vapors are so light that it travels high up in the air and combine
with dust and smoke to form cloud droplets or crystals of water(also
called snow crystals).
the droplets or crystals combine with each other
and increase in size.
So we can say clouds are nothing but visible mass
of liquid droplets.
The process of CLOUD FORMATION takes place high up in
the sky as the temperature there is much cooler as compared to the one
near the ground.
cloud can have droplets as well crystals but it depends
on temperature.
But these drlets are soo tiny and light that it cannot
fall so they remain as a cloud.
Here the water in the vapour form is converted to liquid droplets so we
call this process as CONDENSATION.
The same process can be observed when we boil water with closed lid.
The
steam or vapour condenses to give us water droplets on the lid.
Whether we see it or not, This cloud formation occurs continuously untill
it reaches a point where it cannot hold any more water droplets.
In other
words we can say it has reached its saturation.
Here the tiny light
droplets starts combining with each other to form large droplets.
The
larger droplets are so heavy that it starts falling.
STEP 3- PRECIPITATION
And this atmospheric water then reaches the land either in the form of
rain or snow.
we call this process as PRECIPITATION which is a latin word
meaning to fall from.
How big do you feel are these raindrops?
They are smaller than a
centimeter.
It ranges from 0.25 cm to 0.6 cm.
Some findings says that many planets of our solar system receive rainfall
but this is different from that of our planet earth.
Like rain on venusb
is made of sulphuric acid and due to the intense heat it vaporizes before
it reaches the surface.
On reaching the land surface the water is distributed in different parts:
The water either flows off directly into rivers, oceans, lake which are
the surface water body and this process is called SURFACE RUN OFF.
Some amount of water seeps down or diffuses into the ground by gravity
to give us ground water.
Friends have you seen how the water immediately
seeps down when we water the plants in a pot.
So ground water formation
happens in a similar way and this is called PERCOLATION.
Or infilteration
Friends did you observe something.
The water has actually returned to
where it was earlier present.
thus completing a cycle.
This process of
evaporation condensation and precipitation which maintains a continuous
circulation of water in the nature is called water cycle or hydrological
cycle.
So the various water bodies are continuously replenished through water
cycle.
But which of these water bodies you think would serve as sources
of water for our day to day use?
To find the answer to this question tune into our coming session.
I hope
you liked this session.
Till we meet the next time keep watchin keep
learning .thank you