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Changing state

Introduction

Solid, liquid and gas are called the three states of matter. Materials can be changed from one state to another by heating or cooling. Water moves around the environment in the water cycle.

This section includes:

• States of matter
• The water cycle

States of matter

Solid, liquid and gas are called the three states of matter.
Materials can be changed from one state to another by heating or cooling.

Heating

• If ice (solid) is heated, it changes to water (liquid). This change is called melting.
• Water (liquid) can change to water vapour (gas). This is called evaporation.
• If water (liquid) is heated until it boils, it changes to water vapour (gas) very quickly.

Cooling

• If water vapour (gas) is cooled, it changes to water (liquid). This change is called condensing.
• If water (liquid) is cooled, it changes to ice (solid). This change is called freezing.

The water cycle

Water on the earth is constantly moving. It is recycled over and over again. This recycling process is called the water cycle.

a. Water evaporates into the air
The sun heats up water on land, and in rivers, lakes and seas and turns it into water vapour. The water vapour rises into the air.

b. Water vapour condenses into clouds
Water vapour in the air cools down and changes back into tiny drops of liquid water, forming clouds.

c. Water falls as rain
The clouds get heavy and water falls back to the earth in the form of rain or snow.

d. Water returns to the sea
Rain water runs over the land and collects in lakes or rivers, which take it back to the sea. The cycle starts all over again.

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