NCERT 7th Class (CBSE) Science: Winds, Storms and Cyclones

Question: You may have seen holes made in huge hoardings. Why are these necessary?

Answer: The holes in the hoardings are necessary to reduce the air pressure so that the air instead of applying force on the hoarding passes away from the holes.

Question: News in a newspaper; ‘A cyclone, that started in the desert of Rajasthan, hits Delhi today’. Is the news item correct? Give reasons.

Answer: The news item is not correct because a cyclone generally originates from a sea but Rajasthan is a desert area which is not near a sea.

Question: In winter in regions near the equator why does wind blow from land to sea?

Answer: In winter in regions near the equator wind blows from land to sea because the sea is warmer than the land due to which atmospheric and temperature difference is created. So the direction of wind is from land to sea.

Question: Suppose the earth rotated from east to west, instead of from west to east. How would this affect the pattern of winds circulation on the earth?

Answer: If the earth rotated from east to west to east then the winds in the northern hemisphere would swerve to the left instead of right and the winds in the southern hemisphere would swerve to the right instead of left.

Question: Suggest two methods to find out wind direction at a given place.

Answer: The following are the two methods to find out the direction of wind:

1. While flying a kite, air exerts pressure on the kite due to which the kite flies. The direction in which the kite flies is the direction of blowing of wind.
2. While riding a bicycle, the direction in which it is difficult to ride is opposite to the direction of the blowing wind.

Therefore, while flying a kite or riding a bicycle, the wind direction at a given place can be determined.

Question: State two experiences that made you think that air exerts pressure.

Answer: Two experiences are:

1. We have experienced that when we blow a balloon, the balloon becomes tight. If we try to fill more air, then the balloon will burst after an extent. This happens because air exerts pressure.
2. We have also experienced the movement of fringes of windows and doors of our houses when wind blows in a high speed. This also happens because air exerts pressure.