Class 7 Winds, Storms-Cyclones

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1. What is air pressure?

Ans. The air pressure which is exerted by the weight of air presents in the atmosphere above us. Air exerts pressure in different ways under different situations. For example:

(i) Air enclosed in a container (like a balloon or bicycle tube) exerts pressure.

(ii) Air in the atmosphere around us exerts pressure, and

(iii) Moving air (called the wind) exerts pressure.

1. When a bicycle tube is overfilled with air, it may burst, why does this happen?

Ans. Air is a mixture of so many different gases. Air is made up of tiny particles called ‘molecules’ which move around quickly in all directions. When we put air in a closed container (say, a bicycle tube), the fast-moving air molecules ‘collide’ with the walls of the container and exert a force on the walls of the container from inside. The force produces pressure.  Now, If we put more air into the container, then the container will have more air molecules in it. So the pressure is higher. When the pressure of air will be higher than the capacity of the tube, the tube may burst.

1. Why do the leaves of trees, flags and banners flutter when the wind is blowing?

Ans. It is due to the pressure exerted by moving air (or wind) that the leaves of trees, flags and banners flutter when the wind is blowing.

1. What conclusion do you get from the fact that it is easier to row a boat if there is the wind coming from behind you?

Ans. The blowing wind exerts a pressure on us in the same direction in which our boat is moving and makes our boat moves faster.

1. Explain why smoke always rises up.

Ans. Smoke always rises up as hot air is lighter (lower density than cold air), so smoke rises upwards.

1. Why is it difficult to ride a bicycle while moving against the wind?

Ans. It is difficult to ride a bicycle against the direction of wind because in this case, the blowing wind exerts a pressure on us in the opposite direction in which our bicycle is moving. So, the wind blows in opposite direction to the motion of the object, it makes the movement of the object difficult.

1. What is a thunderstorm?

Ans. A violent storm of thunder and lightning is called a thunderstorm. A thunderstorm is also known as an electrical storm. Generally, a thunderstorm requires three conditions to form

(1) moisture, (2) an unstable air mass and (3) a lifting force.

1. What is a cyclone?

Ans. A cyclone is a huge revolving storm caused by very high-speed winds blowing around a central area of the low-pressure zone over the ocean. The area of very low pressure at the centre of the cyclone is called its eye.

Once a cyclone is formed, it begins to move over the surface of the ocean. The speed of the wind in the cyclone is more than 120 km/h. A cyclone needs a constant supply of warm and moist air. As the cyclone reaches the land, the supply of warm and moist air gradually stops and the cyclone dies down.

1. What would happen if high-speed winds blow over a house having a weak tin roof? Give a reason for your answer.

If high-speed winds blow over the roofs of houses, they will reduce the air pressure above the roofs. And if the roofs of houses are weak, then higher air pressure from below lift up the roofs which can then be blown away by the fast winds.  Thus weak roofs of houses can be lifted and blown away by high-speed winds during a windstorm.