WATER, class 7 geography lesson 5, cbse

The sun’s heat causes evaporation of
water vapor.
When the water vapor cools down, it
condenses and forms clouds. From there it
may fall on the land or sea in the form of
rain, snow or sleet.
The process by which water continually
changes its form and circulates between
oceans,atmosphere and land is known
as the water cycleabdul shumz kv kanjikode 2

Condensation
Precipitation
Run off
EVAPORATION
abdul shumz kv kanjikode 3

Our earth is like a terrarium. The same water
that existed centuries ago still exists today.
The major sources of fresh water are the
rivers, ponds, springs and glaciers.
The ocean bodies and the seas contain salty
water. The water of the oceans is salty or
saline as it contains large amount of
dissolved salts. Most of the salt is sodium
chloride or the common table salt that you
eat. abdul shumz kv kanjikode 4

Three-fourth of the earth
surface is covered by water.
If there is more water than
land on this earth, why do
so many countries face
water scarcity?

Oceans : 97.3 Saline Water
Ice-caps : 02.0
Ground water : 0.68
Fresh Water
Fresh water lakes : 0.009
Inland seas &
Salt lakes : 0.009
Atmosphere : 0.0019
Rivers : 0.0001
100.00
Is all the water on earth available to us? The
following
table gives the distribution of water in
percentage.
Fresh Water

Salinity is the
amount of salt in
grams present in
1000 grams of water.
The average salinity
of the oceans is 35
parts per thousand.

Water is absolutely essential for
survival.
Water alone can quench our thirst
when we are thirsty.
Now don’t you think we are wasting a
precious resource when we use water
carelessly?

Why water is important for us?
• Suggest some ways in which water can be conserved in your
home and in your school

Unlike the calm waters of ponds and
lakes, ocean water keeps moving
continuously.
It is never still.
The movements that occur in oceans
can be broadly categorized as:
waves, tides and currents.

Pacific Oceanabdul shumz kv kanjikode 12

When the water on the
surface of the ocean rises
and falls alternately, they are
called waves.

During a storm, the winds blowing at very high
speed form huge waves. These may cause
tremendous destruction.
An earthquake, a volcanic eruption or underwate
landslides can shift large amounts of ocean water
As a result a huge tidal wave called tsunami,
that may be as high as 15m., is formed.
The largest tsunami ever measured was 150m.
high.

Tsunami is a Japanese word that means
“Harbour waves” as the harbours get
destroyed whenever there is tsunami.
Waves are formed
when gentle winds
scrape across the
ocean surface. The
stronger the wind
blows, the bigger
the wave becomes.
March 22 is
celebrated as World
Water Day when the
need to conserve
water is reinforced in
different ways.abdul shumz kv kanjikode 16

The rhythmic rise and fall of ocean
water twice in a day is called a tide.
It is high tide when water covers
much of the shore by rising to its
highest level.
It is low tide when water falls to its
lowest level and recedes from the
shore.

The strong gravitational pull exerted by the
sun and the moon on the earth’s surface
causes the of the earth closer to the moon
gets pulled under the influence of the
moon’s gravitational force and causes high
tide. During the full moon and new moon
days, the sun, the moon and the earth are
in the same line and the tides are highest.
These tides are called spring tides.

But when the moon is in its first
and last quarter, the ocean waters
get drawn in diagonally opposite
directions by the gravitational pull
of s un and earth resulting in low
tides.
These tides are called :

High tides help in navigation.
They raise the water level close to the
shores. This helps the ships to arrive
at the harbor more easily.
The high tides also help in fishing.
The rise and fall of water due
to tides is being used to generate
electricity in some places.

Ocean currents are streams of
water flowing constantly
on the ocean surface in definite
directions.
It may be warm or cold.

Generally, the warm ocean currents
originate near the equator and move
towards the poles. The cold currents carry
water from polar or higher latitudes to
tropical or lower latitudes. The Labrador
Ocean current is cold current while the
Gulf Stream is a warm current.

The ocean current influence the temperature
conditions of the area.
Warm currents bring about warm temperature
over land surface. The areas where the warm
and cold currents meet provide the best fishing
grounds of the world. Seas around Japan and
the eastern coast of North America are such
examples.
The areas where a warm and cold current meet
also experience foggy weather making it difficult
for navigation.

Ocean Currentsabdul shumz kv kanjikode 24

1. Answer the following questions.
(i) What is precipitation?
(ii) What is water cycle?
(iii) What are the factors affecting the height of the
waves?
(iv) Which factors affect the movement of ocean
water?
(v) What are tides and how are they caused?
(vi) What are ocean currents?

(i)Ocean water is salty.
(ii) The quality of water is
deterioting.

(i) The process by which water continually
changes its form and circulates between
oceans, atmosphere and land
(a)Water cycle (b) Tides (c) Ocean currents
(ii) Generally the warm ocean currents originate
near
(a) Poles (b) Equator (c) None of these
(iii) The rythmic rise and fall of ocean water
twice in a day is called
(a) Tide (b) Ocean current (c) Wave

(i) Caspian Sea Largest lake
(ii) Tide Periodic rise and fall of water
(iii) Tsunami Strong seismic waves.
(iv) Ocean currents Streams of water moving
in definite paths.

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WATER, class 7 geography lesson 5, cbse

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