Measurement of Length and Motion Class 6 Notes

Journey Through the States of Water: Water is one of the most essential substances in our lives. We use water for drinking, cooking, cleaning, farming, and many other purposes. Water is found in nature all around us – in rivers, ponds, lakes, oceans, seas, underground and even in the air. Water exists in three different forms or states. These states are solid, liquid and gas. We can change water from one state to another by heating or cooling it.

Three States of Water

Water exists in three states, which are:

• Solid (Ice): If we make water very cold, it freezes and turns into ice. Ice is the solid form of water. We can see it in the form of ice cubes or in the form of snow or frost on the ground in cold weather. Ice is hard and cold.
• Liquid (Water): The liquid form of water is what we use every day for drinking and cleaning. It has no fixed shape and takes the shape of the container or vessel in which it is placed.
• Gas (Water Vapour or Steam): When we heat water on a stove, it boils and changes into a gas called water vapour or steam. We cannot see water vapour easily, but we can feel it as hot steam while cooking.

Change of State

Water changes from one state to another when we heat or cool it. The changes of state of water are:

• Melting: If we heat ice, it melts and turns into liquid water.

• Example: Ice cubes melting in a glass of water.

• Freezing: If we cool water, it turns into ice. This is called the freezing process.

• Example: Water turning into ice when kept in a freezer.

• Evaporation: If we heat water, it changes into water vapour. This is called the evaporation process.

• Example: Wet clothes drying under the sun.
• Condensation: When water vapour in the air cools down, it changes back into liquid water. This is called the condensation process.

• Example: Water droplets on the outside of a cold glass of water.

• Sublimation (Special Case): Sometimes, solid ice can directly change into vapour without first becoming liquid. This is called sublimation. This is the special property of dry ice.

Water Cycle

The water cycle is the natural process through which water continuously moves around the Earth. The four main steps in the water cycle are:

• Evaporation: The heat from the Sun changes water from oceans, rivers and lakes into water vapour.
• Condensation: Water vapour in the air cools and changes into tiny drops of water that form clouds.
• Precipitation: Clouds become heavy and the water falls back down as rain, snow or hail.
• Collection: Rainwater is collected in rivers, lakes and oceans and the cycle continues.

The water cycle helps in causing rain and keeping water available on Earth.

Importance of Water

Water is important because:

• All living things need water to survive.
• Plants use water to prepare food through the process of photosynthesis.
• Animals and humans need water for drinking and to stay healthy.
• Water is used for cleaning, cooking and growing crops.