Chapter 14: NATURAL RESOURCES 9th

1.       But since land gets heated faster than water, the air over land would also be heated faster than the air over water bodies.

2.       So, if we look at the situation in coastal regions during the day, the air above the land gets heated faster and starts rising.

3.       As this air rises, a region of low pressure is created and air over the sea moves into this area of low pressure.

4.       The movement of air from one region to the other creates winds.

5.       During the day, the direction of the wind would be from the sea to the land.

6.       At night, both land and sea start to cool.

7.       Since water cools down slower than the land, the air above water would be warmer than the air above land.

How movement of air takes place?

1.       All the movements of air resulting in diverse atmospheric phenomena are caused by the uneven heating of the atmosphere in different regions of the Earth.

2.       But various other factors also influence these winds.

3.       They are the rotation of the Earth and the presence of mountain ranges in the paths of the wind is a couple of these factors.

RAIN

A.     How clouds are formed and bring us rain?

B.      What happens when air with a very high content of water vapour goes from a region of high pressure to a region of low pressure or vice versa?

1.       When water bodies are heated during the day, a large amount of water evaporates and goes into the air.

2.       Some amount of water vapour also gets into the atmosphere because of various biological activities.

3.       This air also gets heated. The hot air rises up carrying the water vapour with it.

4.       As the air rises, it expands and cools.

5.       This cooling causes the water vapour in the air to condense in the form of tiny droplets.

6.       This condensation of water is facilitated if some particles could act as the ‘nucleus’ for these drops to form around.

7.       Normally dust and other suspended particles in the air perform this function.

8.       Once the water droplets are formed, they grow bigger by the ‘condensation’ of these water droplets.

9.       When the drops have grown big and heavy, they fall down in the form of rain.

10.   Sometimes, when the temperature of air is low enough, precipitation may occur in the form of snow, sleet or hail.

11.   Rainfall patterns are decided by the prevailing wind patterns.

12.   In large parts of India, rains are mostly brought by the southwest or north-east monsoons.

13.   The ‘depressions’ in the Bay of Bengal causes rains in some areas.

AIR POLLUTION

A.     What is air pollution?

B.      What are causes of air pollution?

C.     What are hazards of air pollution?

D.     What are control measures?

E.      How is the quality of air affected and how does this change in quality affect us and other life forms?

“The undesirable change in the quality of natural air composition is called as air pollution”.

Causes:

1.       The fossil fuels like coal and petroleum contain small amounts of nitrogen and sulphur.

2.       When these fuels are burnt, nitrogen and sulphur too are burnt and this produces different oxides of nitrogen and sulphur.

3.       Not only is the inhalation of these gases dangerous, they also dissolve in rain to give rise to acid rain.

4.       The combustion of fossil fuels also increases the amount of suspended particles in air.

5.       These suspended particles could be un-burnt carbon particles or substances called hydrocarbons.

6.       Presence of high levels of all these pollutants causes visibility to be lowered, especially in cold weather when water also condenses out of air. This is known as smog and is a visible indication of air pollution.

Effects:

7.       Studies have shown that regularly breathing air that contains any of these substances increases the incidence of allergies, cancer and heart diseases.

8.       An increase in the content of these harmful substances in air is called air pollution.

Water: A Wonder Liquid

1. Why do organisms need water?

2. What is the major source of fresh water in the city/town/village where you live?

3. Do you know of any activity which may be polluting this water source?

What are the different forms of water available on earth?

1.       Water occupies a very large area of the Earth’s surface and is also found underground.

2.       Some amount of water exists in the form of water vapour in the atmosphere.

3.       Most of the water on Earth’s surface is found in seas and oceans and is saline.

4.       Fresh water is found frozen in the ice-caps at the two poles and on snow covered mountains. 

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