Energy & Change
Sources of energy, heat transfer, insulation
Sources of Energy
Energy makes things happen — it lets us move, heat food and power machines. Energy comes from different sources:
• Renewable: solar, wind, water (hydroelectric) — they won't run out
• Non-renewable: coal, oil, natural gas — they will eventually run out
South Africa gets most of its electricity from coal through Eskom.
Heat Transfer
Heat moves in three ways:
• Conduction — through solids (a metal spoon in hot tea gets warm)
• Convection — through liquids and gases (hot air rises)
• Radiation — through empty space (heat from the sun reaching Earth)
Example
Insulation
An insulator slows down heat transfer. Examples:
• A woollen blanket keeps you warm (traps air)
• A flask keeps drinks hot or cold (vacuum between walls prevents conduction and convection)
• Ceiling insulation in homes reduces heat loss in winter and keeps homes cool in summer — important for saving electricity in South Africa.
Note
Energy and South Africa
Load-shedding is caused by insufficient electricity supply. South Africa is investing in renewable energy (solar farms in the Northern Cape, wind farms in the Eastern Cape) to reduce dependence on coal.
Key Vocabulary
EnergyThe ability to do work or cause change
RenewableAn energy source that can be replaced naturally
ConductionHeat transfer through direct contact in solids
ConvectionHeat transfer through the movement of liquids or gases
RadiationHeat transfer through electromagnetic waves
InsulatorA material that slows down heat transfer
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