Water – The combination of hydrogen and oxygen is called water.
Water is one of the five elements which form the ‘Panchatatva’.
It is essential for our life.
It is a part of the natural environment.
When we think of water, we think of rivers, sea, waterfall, rains etc.
Water vapour cools to form clouds and from clouds we get rain, snow or sleet.
Properties of water:
Colourless, Tasteless, odourless.
Flows from high level to two level
Freezing point is 0 degree Celsius
Boiling point is 100 degree Celsius
Water Cycle – The process by which water continually changes its form and circulates between oceans, atmosphere and land is called the water cycle.
Our earth is like a terrarium.
The same water that existed centuries ago still exists today.
![cycle_water_1494.png]()
Fresh water sources:
These include the rivers, ponds, springs and glaciers.
Salty water source:
Ocean bodies and seas form a part of this.
The water of the ocean is saline because it contains huge amounts of dissolved salts.
Most of this salt is sodium chloride commonly known as the common table salt that we eat daily.
Distribution of Water:
Three – fourths of the earth’s surface is covered by water.
But most of this water is available as saline water in oceans and seas.
Freshwater is a small fraction of total water on earth.
Due to this, in spite of living on the Blue Planet, we face shortage of drinking water.
Since water is very important for us and scarce too.
We must take measures for conservation of this precious resource.
The following table shows the distribution of water in percentage:
|
Water Body
|
Percentage
|
|
Ocean
|
97.3
|
|
Ice-caps
|
2.0
|
|
Groundwater
|
0.68
|
|
Freshwater Lakes
|
0.009
|
|
Inland Sea and Salt Lakes
|
0.009
|
|
Atmosphere
|
0.0019
|
|
Rivers
|
0.0001
|
|
Total
|
100
|
Some of the steps to prevent wastage of water are as under:
Close taps when not in use
Repair all tap leakages immediately
Do rainwater harvesting
Use water filled in the bucket for bathing instead of a bath tub/shower.
Ocean circulation:
Unlike the calm waters of a pond or lakes, ocean water keeps moving continuously.
These movements can be classified into:
Waves
Currents
Tides
Wave – When the water on the surface of the ocean rises and falls alternately, they are called waves.
They are formed when winds scrape the ocean floor.
When we throw a ball in the ocean, it gets washed back to the shore by the waves.
The stronger the wind blows, the bigger the wave becomes.
During a storm, the wind blows at a very high speed forming huge waves.
These may cause tremendous destruction.
The following can shift large amounts of ocean water:
An earthquake
A volcanic eruption
Underwater landslide
Tsunami – A long, high sea wave caused by an earthquake or other disturbance is called tsunami.
Due to the above, a huge tidal wave called tsunami is formed.
It may be as high as 15 metres.
The highest tsunami ever measured was 150 m high.
These waves travel at a speed of 700 km/h.
Tides – The rhythmic rise and fall of water twice in a day is called a tide.
Tides are caused by the strong gravitational pull exerted by the sun and the moon on the earth’s surface.
The rise and fall of water due to tides is used for generating electricity in some places.
The water of the earth closer to the moon gets pulled under the moon’s gravitational force and causes a high tide.
![Types+of+Tides+Two+types+of+tides_+Spring+Tides+Neap+Tides.jpg]()
Spring Tides: During the full moon and new moon days, the sun, the earth and the moon are in the same line and the tides are the highest. These tides are called spring tides.
Neap Tide: When the moon is in its first and third quarters, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of the sun and the earth. This results in low tides; called neap tides.
Advantages of High Tide:
They help in navigation.
They raise the water level close to the shores and help the ships to arrive at the harbour more easily.
They help in fishing.
More fish come closer to the shore during high tides.
This helps the fishermen to have a good catch and earn more.
Ocean Current – A continuous, directed movement of sea water generated by a number of forces acting upon the water is called ocean current.
OR
Streams of water flowing continuously on the ocean’s surface in definite directions are called ocean currents.
They are streams of water flowing continuously on the ocean’s surface in definite directions.
They influence the temperature conditions of the area. They may be warm or cold.
Ocean current
|
Warm Current
|
Cold Current
|
|
They originate near the equator and move towards the poles.
The Gulf Stream is a warm current.
They bring warm temperature over land surface.
|
They carry water from polar or higher latitudes to tropical or lower latitudes.
For example; the Labrador Ocean Current.
They result in cold temperature over the land surface.
|
Effect of the meeting of warm and cold currents:
They provide the best fishing grounds of the world.
Some example of these is: Seas around Japan and Seas around the eastern coast of North America.
They lead to foggy weather which makes navigation difficult.
Do You Know?
The average salinity of the ocean is 35 parts per thousand.
Dead Sea in Israel has salinity of 45 parts per thousand.
Swimmers can float in it because the increased salt content makes it dense.
World Water Day is celebrated on March 22.
On this day the need for conservation of water is reinforced.
Tsunami is a Japanese word. It means the ‘harbour waves’ as the harbours get destroyed whenever there is a tsunami.
