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Properties of Matter and Composition of Air - Grade 6 Science

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Properties of Matter - Expansion and Contraction

Expansion And Contraction In Liquids

- When a water in a bottle is heated, its volume increases. The increase in volume due to heating is called expansion.
- When the water cools, its volume decreases. This decrease in volume due to cooling is called contraction.

Expansion And Contraction Of Gases

Expansion and contraction of gases - Science and Technology Grade 6
The balloon is inflated when the bottle is placed in hot water, and deflates when the bottle is placed in cold water.
- Air expands on heating and contracts on cooling.

Expansion And Contraction In Solids

Expansion and contraction of solids - Science and Technology Grade 6
Before heating, the cold metallic ball easily goes through the ring. Once heated, the now hot metallic ball does not go through the ring.
- Solid expands when heated and contracts when cooled.

Application Of Expansion And Contraction

(i) It is used in thermometers.
- The liquid inside the thermometer expands when heated and contracts when cooled.

(ii) Electric power lines are loosely fixed during construction.
- This allows the space for expansion and contraction during hot and cold seasons.

(iii) The road engineers use the principle of expansion and contraction when making bridges.
- One end of the bridge is given some space for expansion and contraction during hot and cold seasons.

(iv) The railway lines are left with spaces between the metal rails.
- This allows enough space for expansion and contraction.

Composition of Air

- Air is a mixture of gases.
- The major gases that are found in the air are:
  • Nitrogen - 785%
  • Oxygen - 21%
  • Carbon dioxide - 0.03%
  • Inert gases - 0.97%

Uses of oxygen

- Oxygen is used in burning.
- Oxygen is used in germination.
- Oxygen is used in breathing.

Uses of carbon dioxide

1. Photosynthesis.

-This is the process by which green plants make their own food.
- Green plants use carbon dioxide to make food during the day and release oxygen to the atmosphere.
- Therefore, they clean air.

2. Preservation of soft drinks

- Carbon dioxide is added in soft drinks to preserve them.
- Therefore they can last for longer time.

3. Making fire extinguishers

- Carbon dioxide does not support burning.
Therefore, it is used to put out fire.

Uses of nitrogen

1. In leguminous plants

- Leguminous plants such as beans, peas and clovers use nitrogen from air in the soil to make proteins.

2. In food preservation/packaging

- Nitrogen is used in food packaging containers to keep off oxygen in order to make the food last longer.

3. In light bulbs

- To prevent the filament from burning.

4. In making fertilisers

- Nitrogen is one of the materials used in making fertilisers that are used by plants.

Uses of inert gases

1. Making electric tubes and bulbs.
2. Making advertisement lights.

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