Air: the invisible blanket

We cannot see air, smell clean air or hold it in our hands, yet it is all around us. A thick blanket of air called the atmosphere wraps the whole Earth. We know air is there because we feel it when the wind blows, see it fill a balloon and watch it make leaves dance on a tree.

Air is a mixture of gases. About four-fifths of it is nitrogen and about one-fifth is oxygen, the gas we need to breathe. Air also has a little carbon dioxide, which plants use to make food, along with water vapour, dust and smoke.

Properties of air

• Air takes up space. A balloon swells when we blow air into it.
• Air has weight. A football weighs a little more after we pump air into it.
• Air presses on everything. This push is called air pressure.
• Moving air is wind. Gentle wind is a breeze; very strong winds can become storms and cyclones.

Water: the gift of life

About three-quarters of the Earth is covered with water, but most of it is salty sea water. Only a tiny part is fresh water in rivers, lakes, ponds, wells and under the ground. Plants, animals and people all need water to live. We use it for drinking, cooking, bathing, washing, farming, and even for making electricity in dams.

The water cycle

The water we drink today may once have been in a cloud over the sea. The Sun heats water in seas, rivers and lakes, and some of it turns into invisible water vapour that rises into the air. High up, the air is cool, so the vapour turns into tiny droplets that form clouds. When the droplets join and become heavy, they fall as rain, snow or hail. The water flows back into rivers and seas, and the journey starts again. This never-ending journey is called the water cycle.

What is weather?

Weather is what the air is like at a place at a particular time. Is it hot or cold? Sunny or cloudy? Windy or calm? Dry or rainy? Weather can change from morning to evening. Scientists who study the weather use instruments such as thermometers for temperature, rain gauges for rainfall and wind vanes for wind direction. They share weather forecasts so that farmers, fishermen, pilots and families can plan their day. The usual weather of a place over many years is called its climate.

Seasons in India

India has hot summers, rainy monsoons and cool winters, with pleasant spring and autumn in between. We change our clothes, food and activities with the seasons: cotton clothes and cool drinks in summer, umbrellas and raincoats in the monsoon, and woollens and hot soup in winter.

Keeping air and water clean

Smoke from factories, vehicles and burning garbage pollutes the air, while sewage, plastic and chemicals pollute rivers and lakes. We can help by planting trees, walking or cycling for short trips, never throwing waste into water, saving water at home and collecting rainwater.

This Air, Water and Weather worksheet for Class 4 turns these ideas into an island adventure on WitKnowLearn with an online quiz, online activities and interactive games. Flip the cards, follow water round the Water Cycle Lab, play the games, do the science labs, take the challenges and then carry out drying and filtering experiments in the Virtual Lab.