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
Observation
The balloon is inflated when the bottle is placed in hot water, and deflates when the bottle is placed in cold water.
The balloon is inflated when the bottle is placed in hot water, and deflates when the bottle is placed in cold water.
Expansion And Contraction In Solids
Observation
Before heating, the cold metallic ball easily goes through the ring. Once heated, the now hot metallic ball does not go through the ring.
Before heating, the cold metallic ball easily goes through the ring. Once heated, the now hot metallic ball does not go through the ring.
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.