Air : Class 7 Geography NCERT Chapter 4

Key Features of NCERT Material for Class 7 Geography Chapter 4 – Air 

In the last chapter 3, we studied the earth movements, Different forces associated with it and how it causes volcanos and earthquakes. In this chapter, we will understand the composition and structure of Air. Along with that, we will also look at terms like weather, climate, Air pressure etc.

Quick revision notes

Our environment is encircled by a cover of air called the atmosphere. 

Composition of the Atmosphere 

• Nitrogen and oxygen are the two gases which make up the majority of the climate. 
• Carbon dioxide, helium, ozone, argon and hydrogen are in relatively lesser amounts. 
• Aside from these gases, small dust particles are likewise presently noticeable in the air. 

 Structure of the Atmosphere 

Our air has five layers beginning from the surface of the earth. 

• The primary layer is the Troposphere whose average height is 13 km. The troposphere is the layer wherein the air we inhale exists. Practically all weather phenomena happen here. 
• The next layer is the Stratosphere which reaches out up to 50 km. 
• The third layer is the Mesosphere which stretches out up to the height of 80 km. 
• The fourth layer is the Thermosphere which stretches out from 80 km to 400 km. 
• The topmost layer of the air is the Exosphere which has thin air. 

Weather and Climate

• Weather is the Hour-to-hour, everyday state of the atmosphere. 
• Whereas Climate is the atmospheric conditions for a large period and of a huge region. 

Temperature 

• Temperature is the level of hotness and coldness in the air. 
• The temperature of the atmosphere changes among day and night as well as from season to season, a significant factor that impacts the distribution of temperature is insolation. 
• Insolation is the approaching solar energy captured by the earth and it diminishes from the equator towards the pole. 
• Estimation of temperature is in Celsius and Fahrenheit. 

Air Pressure 

• Air pressure is characterized as the pressure applied by the weight of air on the surface of the earth. 
• Horizontal distribution of air pressure is affected by On a level plane the dispersion of pneumatic the temperature of the air at a given spot. 
• In zones having a lower temperature, the air is cold. 
• The air constantly moves from high-pressure regions to low-pressure regions. 

Wind 

• The development of air from high-pressure regions to the low-pressure regions is called Wind. 
• Winds can be comprehensively divided into three kinds: permanent winds, seasonal winds and local winds. 
• On 25 October 1999, cyclonic winds started as depression and influenced Odisha killing a huge number of individuals. 

Moisture in air

At the point when water evaporates from land and other water bodies, it becomes water vapour. 

Although, Moisture noticeable in the air at any time is known as humidity. 

At the point when the water vapor rises, it begins cooling. The water vapour condenses resulting information of the water droplets.

At the point when these droplets of water become too heavy to float in the air, they descend as precipitation. 

Precipitation is the falling of moistures as rainfall, fog, snow, sleet and hailstones. 

Moreover, Based on the mechanism, there are three different kinds of rainfall: the conventional rainfall, the orographic rainfall and the cyclonic rainfall. 

However, Precipitation is significant for the survival of plants and creatures.

The atmosphere is a thin cover of air that encompasses the earth. It shields us from the harmful beams of the sun.

Air comprises of:

the primary nitrogen (78%) and oxygen (21%).

Carbon dioxide, helium, ozone, argon, and hydrogen are found in relatively lesser amounts. 

Nitrogen is significant for plants. Their survival relies upon this gas. 

Oxygen is basic for people and creatures. Since, they take in oxygen, delivered by green plants during photosynthesis. 

Green plants take in carbon dioxide which is discharged by people and creatures. Along these lines, there is a common connection between the plants and the people or creatures. Consequently, we should protect plants and trees for our own advantage. 

The atmosphere is isolated into five layers:

 beginning from the earth’s surface which is the Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere. 

The troposphere is the layer where the air we inhale exists. Most of the weather phenomena happen here. 

The stratosphere has an ozone gas layer. 

The mesosphere stretches out up to the height of 80 km. Meteorites burn as they enter into this layer from space. 

Thermosphere assists in radio transmission. 

The exosphere is the topmost layer, where the air is very thin. 

Weather is an hour-to-hour, everyday state of the air. 

However, Climate is the common weather state of a place for a more extended timeframe. 

The temperature of the climate stays evolving. Temperature is the level of hotness and coldness in the air.  

Insolation is a significant factor that impacts the distribution of temperature and it’s measure decreases from the equator towards the poles. In this manner, the temperature diminishes similarly. 

The air above us pressures us from all directions with incredible power on our body and so our body applies a counter pressure. 

Air Pressure is the pressure applied by the weight of air on the earth’s surface. As we go up the layers of the climate consequently, the pressure falls quickly. 

Low pressure is connected with wet weather and cloudy skies. High pressure is related to clear and radiant skies. The air constantly moves from high-pressure zones to a low-pressure zone. 

The wind is the development of air from the high-pressure region to the low-pressure region. Even though the wind might be delicate. On occasion, it might be solid and devastating. 

Winds are of three kinds—Permanen winds, Seasonal winds, and Local winds. 

Moisture is humidity. A humid day is such when the air is the fall of water vapor. On a humid day, garments take more time to dry, and sweat from our body doesn’t dissipate easily. 

Clouds are masses of water droplets. At the point when these beads of water become extremely heavy, they descend as precipitation. Precipitation that comes down to the earth in fluid form is rainfall. 

There are three kinds of rain based on mechanism: Conventional rainfall, orographic rainfall, and cyclonic rainfall

Constituents of air

Structure of the atmosphere

Global warming:

When the temperature of the earth’s atmosphere increments because of to the increments in carbon dioxide, it is called global warming.

Weather:

The hour-to-hour, everyday state of the atmosphere is called weather.

Climate:

The average weather condition of a place for a longer time frame is the climate of a place.

Temperature:

The level of hotness and coldness of the air is temperature.

Isolation:

Isolation is the approaching solar energy captured by the earth.

Air pressure:

The pressure applied by the weight of air on the earth’s surface is air pressure.

Wind:

The wind is the movement of air from the high-pressure zones to low-pressure zones.

Moisture:

The water vapour that is present in the atmosphere is known as moisture.

Humidity:

Moisture noticeable in the air is known as humidity.

Cloud:

The mass of water droplets is a cloud.

Precipitation:

Falling of water on the earth surface in the form of rainfall is precipitation.

Thermometer:

It is an instrument that is utilized for the measurement of temperature.

Barometer:

It is an instrument that is utilized to measure atmospheric pressure.

Rain gauge:

The instrument utilized to measure the amount of rainfall.

Wind vane:

Utilization of wind vane is to show the direction of the wind.