Chapter 4- air
Earth is surrounded by a huge blanket of are called atmosphere. Protects us from harmful rays
Composition of the atmosphere
Nitrogen78% oxygen 21%
Other gas- carbon dioxide 0.03% Argon 0.93% All others 0.04%
Plants need nitrogen for their survival Cannot take directly.
Bacteria live in soil and Roots take nitrogen from air and change its form so that plants can use it.
Human or animal release carbon dioxide
Amount of CO2 released by Humans or animals seems to be equal to the amount used by plants.
Balance is upset by burning of wells.
Structure of the atmosphere
Divided into five layers
Troposphere Stratosphere mesosphere thermosphere and exosphere
Troposphere
Most important layer
Average height is 13 kilometer.
Air we breathe, All weather phenomena Like rainfall fog and hailstorm occur in this layer.
Stratosphere
Above troposphere Extends up to a height of 50 kilometer. Free from clouds
Making condition most ideal for flying aeroplanes.
It contains ozone layer.
Mesosphere
Third layer of atmosphere extend up to a height of 80 kilometer.
Meteoroids burn up in this layer
Thermosphere
Temperature rises rapidly with increasing height
Ionosphere is a part of this layer.
Extend between 80 to 400 km
This layer helps in radio transmission
Radio waves Reflected back to the Earth by this layer
Exosphere
Uppermost layer
Very thin air
Light gases like helium and hydrogen
Weather and climate
Weather is day-to-day condition of the atmosphere.
Climate is the average weather condition of a place for a longer period of time.
Temperature The degree of hotness and coldness of the air is known as temperature.
Important factor that influences the distribution of temperature is insolation.
Insolation is the incoming solar energy intercepted by the Earth.
Amount of insolation decreases from equator towards the poles
Temperature decreases in the same manner
Air pressure
Defined as the pressure exerted by the weight of our of air on the Earth's surface.
As we go up the pressure Falls rapidly. Highest at sea level and decreases with height
Horizontal distribution of air pressure is influenced by temperature of air at a given place.
High temperature area, Air gets heated And Rises Creates a low pressure
Low pressure is associated with cloudy skies and wet weather.
Areas having low temperature air is cold there for heavy. Heavier sinks and creates a high pressure
High pressure is associated with clear and sunny skies.
Air always moves from high pressure area to low pressure areas
Wind
Movement of air from high pressure area to low pressure area is called wind.
Broadly divided into three types
Permanent winds-
Trade Winds Westerlies and Easterlies
Blow constantly throughout the year in a particular direction.
Seasonal winds-
These winds changes their Direction in different seasons.
Example monsoon in India
Local winds-
Blow only during a particular period of the day Or year in a smaller area Example Land and Sea Breeze
Moisture
When water evaporates from land and different water bodies, it becomes water vapor.
Moisture in the air at any time is known as humidity.
As the air gets warmer. Its capacity to hold the water vapor increases And so it becomes more and more humid.
When the water vapor Rises it starts Cooling.
Gets condenses causing formation of droplets of water
Clouds are just masses of such water droplets.
When these droplets of water become too heavy to float in air they come down as precipitation.
Jet planes flying in the sky leave a white trail behind them. The moisture from their engines condenses. We see trails of this condensed moisture for some time when there is no air movement to disturb it.
Precipitation that comes down to earth in liquid form is called rain.
There are three types of rainfall on basis of mechanism-
The convictional rainfall
the orographic rainfall
and the cyclonic rainfall
Rainfall very important for survival of plants and animals
Chapter 5 water
The process by which water continually changes its form and circulates between oceans atmosphere and land is known as water cycle.
Major sources of freshwater are rivers ponds Springs and Glaciers.
Ocean bodies and see contain salty water.
Distribution of water bodies
3/4 of the earth's surface is covered by water.
Oceans 97.3%
ice caps 2.0%
Groundwater 0.68%
Freshwater lakes 0.009%
Inland seas and Salt Lake's 0.009%
Atmosphere 0.001 9%
rivers 0.0001%
Ocean circulation
The movement that occur in oceans can be broadly categorized as waves tides and currents.
Waves
When the water on the surface of the ocean Rises and Falls alternatively. They are called waves.
During a storm winds blowing at very high speed from huge waves.
An earthquake or volcanic eruption or underwater landslides can shift large amount of ocean water. As a result a huge tidal wave called tsunami Is formed
The Indira point in Andaman and nicobar Island got submerged after tsunami 2004
Tides
The rhythmic rise and fall of ocean water twice in a day is called a tide.
High tide when water covers much of the shore By rising to its highest level.
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 surface causes the tides.
The water 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 day (the Sun the Moon and the Earth are in the same line and the tides are highest) Called spring tides
But when moon is in its first and last quarter The ocean water gets drawn. It's in diagonally opposite direction by gravitational pull of sun and moon resulting in low tides. These are called neap tides.
High Tides help in navigation Raise the A level close to the shore
Helps ship to arrive at the harbor more easily.
Helps in fishing
Rise and fall of water due to Tides used to generate electricity.
Ocean currents
Streams of water flowing constantly on the ocean surface in definite Direction
Ocean currents may be warm or cold
Warm ocean currents originated near the equator and moves towards the poles.
Cold currents carry water from the polar or higher latitudes to Tropical or lower latitudes.
Labrador ocean current is Cold current while Gulf Stream is a warm current.
Ocean current influence the temperature condition of the area One currents bring about warm temperature over land surface.
Areas, where the warm and cold current meet provide the best fishing ground of world.
Also experience foggy weather making it difficult for navigation.
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