Many of our activities, as well as the activities of plants and animals, are affected by changes in weather. Our food –style, living –styles etc. are also changed due to changes in weather. The sun plays an important role in causing changes in weather. Seasons are formed because of changes in weather.
In summer, it is sunny weather. The sun is more directly overhead. So it is very hot. Days are comparatively longer. During day time, the land becomes warmer quickly than water and at night, land becomes colder quickly than water. In summer, we use white cotton clothes and keep our houses cool.
During winter, cold weather comes. It is extremely cold. Days are comparatively shorter than nights. The mornings are not pleasant as these are foggy. A soon as the sun rises, it becomes clear. In winter, we use woolen garments and keep our houses warm.
The sun plays an important role in causing rains. The rainfall is advantageous as well as disadvantageous. The water changes to water-vapor due to sun rays. It is called evaporation. It takes place at all times. Conditions that favor evaporation are:-
a) windy weather
b) wider exposed surface area
c) higher temperature
d) small humidity of atmosphere
e) Absence of clouds in the sky.
Condensation in nature
If water vapor is cooled, it changes back into water. It is called condensation. So, condensation is a process, in which water vapor changes into water. The changes of steam into water are also called condensation.
During a water cycle, water evaporates from the land, and rises up to in the air. It cools there and the cooling changes water vapor in to the droplets of water. There in forms clouds. When these tiny droplets become larger, they cannot stay in the clouds. They come down in from of rain. Some of the rain water seeps into the deep earth and some evaporates again. This cycle goes on for ever.
When there is much cooling in air, the water drops may change into crystals of ice. These crystals of ice are called hailstones. When hailstone falls along with heavy rains it is called sleet.
When the atmosphere is very cold, water vapors freeze in the air forming minute ice crystals, these are called snow. If however, water vapors condense on dust particles present in air, it is called fog. The fog disappears as soon as the sun appears brightly in the sky.
When the surfaces of plants become very cold, the water vapors condense on leaves of plants and grass. This is called dew. When the ground level gets much cooler than ice, the water is we say that frost is formed.
Presence of water vapor in the air causes humidity. If humidity is large, as on rainy day, evaporation becomes very slow.