7 Geography Chapter 4 Air

Chapter Notes and Summary
• An envelope of air surrounding earth is called atmosphere.
• Air is a mixture of gases; consisting of mainly nitrogen (78%) and oxygen (21%), Carbon-dioxide, helium, ozone, argon and hydrogen.
• atmosphere is divided into five layers—troposphere, stratosphere, mesosphere, thermosphere and exosphere.
Troposphere is layer in which air we breathe exist. Almost all weather phenomenons occur here.
Weather is atmospheric conditions for a specific time at a specific place.
Climate is weather conditions for a large period and of a large area.
Temperature is degree of hotness and coldness of air.
• Temperature is measured in Celsius and Fahrenheit.
• pressure exerted by weight of air on earth’s surface is known as air pressure.
• movement of air from high pressure area to low pressure area is called wind.
Moisture is water vapour present in air.
Humidity is moisture in air.
Precipitation is falling of moisture in form of rainfall, snow, fog, sleet and hailstones.

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