Air, Water and Weather
Air is the Earth’s atmosphere. We are surrounded by air. We cannot see it but can feel the air when it blows. Moving air is called wind. It has no color or smell. Air has an indefinite shape and volume. Air is a matter as it has mass and weight.
Air around us is a mixture of several gases and dust particles. It is a mixture of about 78% nitrogen, 21% oxygen, 0.9% argon, 0.04% carbon dioxide, and very small amounts of other gases. There is an average of about 1% water vapour.
Animals and we human being need the oxygen in the air to live. When we breathe in oxygen, the lungs give oxygen to the blood, and breathe out carbon dioxide in the air. Plants need the carbon dioxide in the air to live. They use carbon dioxide to make food. Plants give out oxygen in the air that humans can breathe again.
Air gets polluted by smoke and some harmful gases such as carbon monoxide given out by vehicles such as cars and buses, and factories. These harmful gases can make us sick when breathe in this polluted air. Air pollution can cause difficulty in breathing, wheezing, coughing and asthma. Thus, we should plant more and more trees to make air free from pollution.
The existence of water is essential for life on Earth. Water covers around 70% of the Earth’s surface.
Water is a liquid. It flows. It is found in rivers, lakes and oceans. It is also present under the ground.
Water is made up of two elements, hydrogen and oxygen. Its chemical formula is H2O. Water has three different states, liquid, solid and gas. The word water usually refers to water in its liquid state. The solid state of water is known as ice while the gas state of water is known as steam or water vapour.
When water is heated for some time, it slowly disappears. It changes into water vapour. Water vapour is a gas. When water is kept in the freezer of a refrigerator, it changes to ice. Ice is a solid. When ice is kept in a warm place, it changes back to water i.e. liquid.
Ice, water and water vapour are the three forms of water.
The heat of the sun warms the water in rivers, lakes and oceans. Due to heat water changes into water vapour i.e. gas and rises up. High above, the air is cool. On cooling, water vapour changes to form tiny drops of water. These drops gather together to form clouds.
When clouds pass through cooler air, they get further cooled. The water drops become bigger. When they become too big, they fall to the ground as rain.
These water goes back into the river, lakes and oceans. It again changes to water vapour due to heat from the sun. This process goes on repeating. This process is called water cycle.
Sometimes when the air is very cold, water in the clouds can freeze to form ice. It then comes down as hail or snow.
Weather is the state of the atmosphere with respect to heat or cold, wetness or dryness, calm or storm, clearness or cloudiness. Because of the sun, air and water, the weather keeps changing. The sun warms the earth. It is hot when the sun is directly above our head. It is not so hot when the sun goes down.
Do you know why the wind blows?
When the sun heats the earth, warm air goes up. The cool air rushes to takes its place. So, the wind blows. When the wind blows very gently, it is called breeze. When wind blows very fast, it is called gale. Sometimes the wind moves with great speed and it rains very heavily. It is called storm. A storm can cause great damage to crops, trees and buildings.
Weather changes occur throughout the year. Sometimes it is hot, sometimes it is cold. Sometimes it rains a lot. In India, we have three main seasons: the summer season, the rainy season and the winter season.
During the summer season the days are very hot. The days are long and warm. We spent much of our time indoors to protect ourselves from heat. We should drink plenty of water to keep our body cool.
During the rainy season, it rains in almost every part of India. Wind blows and clouds become dark and grey. Some parts of India also gets flooded due to rain causing damage to crops and properties.
It is very cold in winter season in many parts of India except southern India. It is not cold in southern India even in winter season. In winter, the days are short and cold. People wear woollen clothes to protect themselves from cold.
Click the Next button given below for solved exercise on chapter – Air, Water and Weather for Class 3.