Matter exists in three main forms called states:

Solids have a definite shape and definite volume. They do not change shape when placed in a different container. Examples: stones, firewood, cooking pots, desks.

Liquids have no definite shape but have definite volume. They take the shape of the container they are placed in. Examples: water, juice, milk, oil.

Gases have no definite shape and no definite volume. They spread out to fill any available space. Examples: air, steam, the air inside a balloon.

We can learn about the states of matter by conducting simple experiments using water, which can exist in all three states.

Experiment 1: Investigating Ice (Solid Water)

Materials: Ice cubes, a saucepan, a jug, a heat source

Procedure:

1. Place an ice cube in a saucepan. Observe its shape and colour.
2. Press the ice cube with your fingers. Does it change shape?
3. Transfer the ice cube to a jug. Does it take the shape of the jug?
4. Place another ice cube on a heat source. What happens?

Results: Ice is colourless and firm. It keeps its own shape even when placed in different containers. It does not flow like water. When heated, ice melts into liquid water.

Conclusion: A solid has definite shape and definite volume.

Experiment 2: Investigating Liquid Water

Materials: Water, a jug, a saucepan, a plastic bag, a cup

Procedure:

1. Pour water into different containers (jug, saucepan, plastic bag).
2. Observe the shape of water in each container.
3. Tilt the containers and watch how water flows.
4. Pour water from one container to another. Does the amount change?

Results: Water has no colour, taste, or smell. It takes the shape of whatever container holds it, but the amount (volume) stays the same. Water flows freely.

Conclusion: A liquid has no definite shape but has definite volume.

Experiment 3: Investigating Steam (Gas)

Materials: Water, saucepan, heat source, mirror

Procedure:

1. Heat water in a saucepan until it boils.
2. Observe what you see rising from the boiling water.
3. Hold a cool mirror above the steam. What do you see?

Results: When water boils at 100°C, it produces water vapour (steam). Steam has no colour or smell. It spreads out to fill any space. When steam touches a cool surface, it turns back into water droplets.

Conclusion: A gas has no definite shape and no definite volume.

Water can change from one state to another when temperature changes:

The freezing point of water is 0°C. The boiling point of water is 100°C.

• Solids have definite shape and definite volume
• Liquids have no definite shape but have definite volume
• Gases have no definite shape and no definite volume
• Temperature causes matter to change between states
• Water exists as solid (ice), liquid (water), and gas (steam)

In Tanzania, understanding the states of matter helps in everyday activities. For example, when cooking mbatata (sweet potatoes) or vegetables, knowing that water boils at 100°C helps ensure food is cooked properly. Fish and meat sellers at the market use ice (solid water) to keep food fresh, because ice at 0°C slows down bacterial growth. Also, when brewing chai or coffee, watching for steam (gas) appearing shows the water is reaching its boiling point and is ready to use.