Energy

Energy resources

Biomass (e.g. wood, crops) is classed as renewable because the plants used can be regrown, reabsorbing carbon dioxide as they grow.

Energy stores and transfers

The chemical energy store holds energy in the bonds of chemicals such as food, fuel, and batteries, released by chemical reactions.

Heat transfer

Dark, matt surfaces are the best emitters and absorbers of thermal radiation; light, shiny surfaces are the worst emitters and best reflectors.

Energy resources

Coal is a non-renewable fossil fuel; burning it releases carbon dioxide and it cannot be replaced on a human timescale.

Energy stores and transfers

Energy cannot be created or destroyed — it can only be transferred from one store to another. The total energy before a process always equals the total energy after.

Heat transfer

Conduction is the transfer of thermal energy through a material by vibrating particles passing energy to neighbouring particles, without the particles themselves moving far.

Energy resources

A fossil fuel is a fuel formed over millions of years from the remains of ancient living organisms; coal, oil and natural gas are fossil fuels.

Energy stores and transfers

In any energy transfer, some energy is always dissipated (spread out) to the surroundings as thermal energy (heat) — this is called wasted energy.

Heat transfer

Convection occurs because heating a fluid makes it expand, become less dense, and rise; the cooler, denser fluid sinks to replace it.

Energy resources

Burning fossil fuels releases carbon dioxide, a greenhouse gas that contributes to climate change.