Maharashtra Board Class 7 Geography Chapter 5 Winds PDF Download

Winds

See outside the window of your classroom. Which objects are moving? Which are still?

Which objects are moving on their own?

Which objects are not moving on their own? Why?

We feel the wind but cannot see it. When certain objects in our surroundings move, we experience wind. The movement of air is called wind. Why does air move?

Try This

Fold a paper into two same-sized rolls.

Keep both the paper rolls on one side of a table.

You and your friend should select one roll each.

Without touching the role of the paper or the table, what can be done to move the paper rolls to the other end of the table?

See who moves the paper roll first to the other end of the table.

What could be the reason of the delay in making the rolls reach to the other end of the table?

What can we do to move the rolls to the other end of the table with a greater speed?

Can a bottle filled with water be moved to the other end of the table in this manner? Can we use the same method that you tried for moving the paper rolls?

Teacher's Note

Wind is moving air. We feel wind when it pushes things. Just like a fan makes air move in your home, the sun makes air move on Earth.

Exam Trick

Remember: Wind = Moving air. Air moves from high pressure to low pressure areas. Think of air like water flowing downhill from high to low places.

Points to Remember

Wind is the movement of air.
We cannot see wind, but we feel it.
Air moves from high pressure areas to low pressure areas.
Wind speed is measured in knots or kilometres per hour.
Winds are named by the direction they blow from.

Geographical Explanation

We have learnt that the air pressure is not uniform across the earth's surface. Air moves from high pressure areas towards low pressure areas in a horizontal manner. Winds are generated due to this movement.

The extent of the difference in the air pressure affects the velocity of the wind. If there is less difference in the pressure, winds blow with less velocity. Winds blow with greater velocities if the pressure difference is greater. Wind speed also varies. Wind velocity is measured in the units of knots or kilometres per hour.

Winds are known by the direction from which they blow. For example, Westerlies are winds that blow from the west. The direction of blowing, the duration, the regions covered, and the condition of the air determine the following wind types:

Planetary Winds

Some winds blow regularly on the earth from high to low pressure belts throughout the year. These winds cover a large portion of the earth, hence these are called planetary winds. For example, the Easterlies, the Westerlies and the Polar winds.

In both the hemispheres, the winds blow from the high pressure area between 25° and 35° parallels, to the equatorial low pressure belt. Due to the rotation of the earth, their original direction changes. In the northern hemisphere, they blow from the north-east to the south-west whereas in the southern hemisphere they blow from the south-east to the north-west. These winds coming from both the sides converge near the equatorial calm belt. These winds are known as the Easterlies.

In both the hemispheres, winds blow from the mid-latitudinal high pressure belt to the subpolar low pressure belt situated near 60° parallel. Their original direction changes due to the rotation of the earth. In the southern hemisphere, these winds blow from the north-west to the south-east and in northern hemisphere, they blow from the south-west to the north-east. These winds are called Westerlies.

In both the hemispheres, winds blowing from the polar high pressure belt to the subpolar low pressure belt (55° to 65°) are called Polar winds. Generally, they blow from east to west.

Teacher's Note

Planetary winds blow all year round over large areas of Earth. In India, we feel the north-east and south-west winds as part of these planetary wind systems.

Exam Trick

Remember three planetary winds: Easterlies (near equator), Westerlies (middle latitudes), and Polar winds (near poles). Think "E-W-P" for East-West-Polar.

Points to Remember

Planetary winds blow regularly all year.
Easterlies blow from 25° to 35° towards the equator.
Westerlies blow in the middle latitude regions.
Polar winds blow near the North and South Poles.
Earth's rotation changes the direction of these winds.

Can You Tell?

Observe figure and answer:

Which are the winds in the northern hemisphere that blow from the mid-latitudinal high pressure belt to the equatorial low pressure belt?

What is the direction of the Westerlies in the southern hemisphere?

Which planetary winds blow from the mid-latitudinal high pressure belts to the subpolar low pressure belts in the northern hemisphere?

Why is the direction of polar winds not the same in both the hemispheres?

Name the winds that blow in the southern hemisphere?

In which direction do the Easterlies blow in the northern and southern hemispheres?

Give It A Try

Write the changed direction of the wind in the table below:

When we consider the earth as a whole, we find the direction of the winds is influenced by the rotation of the earth. In the northern hemisphere, winds get deflected towards the right of their original direction, whereas in the southern hemisphere they get deflected toward the left of their original direction. This direction has been shown by curved arrows in the figure. The rotation from west to east causes this change in the original direction of the winds.

Teacher's Note

Earth's rotation changes wind direction. In the northern hemisphere, winds turn right. In the southern hemisphere, winds turn left. This is like how a spinning top makes balls curve when rolled on it.

Exam Trick

Remember: North turns Right, South turns Left. Use "NR, SL" to remember how winds deflect in each hemisphere.

Points to Remember

Earth's rotation deflects winds in different directions.
Northern hemisphere winds turn to the right.
Southern hemisphere winds turn to the left.
This deflection is called the Coriolis effect.
Wind direction depends on which hemisphere you are in.

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