Conservation and Dissipation of Energy

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infoWhy this? Although energy is conserved, transfers often dissipate energy to the surroundings, reducing its usefulness. Understanding efficiency, insulation, and renewable and non-renewable resources enables us to compare technologies and evaluate their economic and environmental consequences using evidence.

scheduleWhy now? Following Energy Changes, this unit applies the energy-stores and transfer model to homes, machines, and large-scale energy supply. Existing skills in calculating energy and power now support efficiency calculations and informed analysis of resource choices and climate impacts.

Useful energy is the energy transferred to where it is wanted in the form it is needed.
Wasted energy is energy that is not usefully transferred and is often dissipated to the surroundings, usually as thermal energy.
Wasted energy is eventually transferred to the environment, making it less useful as it spreads out.
Thermal energy is commonly lost from houses through the roof, windows, walls, floors, and doors.
Insulation reduces the rate of heat transfer from homes by providing materials that are poor conductors of heat.
Efficiency is the proportion of input energy that is usefully transferred, usually expressed as a percentage.
Machines waste energy mainly as heat due to friction, sound, and other non-useful transfers.
Efficiency cannot exceed 100%; in most real devices, some energy is dissipated to the surroundings, although a transfer may be 100% efficient when all outputs are useful for its intended purpose.
Energy transfers can be made more efficient by reducing wasted energy, for example by lubrication, insulation, or streamlining.
The main energy sources include fossil fuels (coal, oil, and natural gas), nuclear, solar, wind, hydroelectric, tidal, geothermal, and biomass.
Renewable energy resources are those that can be replenished naturally on a human timescale, such as solar, wind, hydroelectric, tidal, geothermal, and biomass.
Non-renewable energy resources are those that cannot be replenished on a human timescale, such as coal, oil, natural gas, and nuclear fuels.
The use of different energy resources has environmental impacts, such as greenhouse gas emissions, air pollution, habitat destruction, radioactive waste, and resource depletion.

rocket_launchYou must be able to

Identify and distinguish between useful and wasted energy in a range of energy transfers and devices.
Identify where and how thermal energy is lost from a house using diagrams or descriptions.
Compare the effectiveness of different types of insulation using data such as U-values, cost-effectiveness, and payback time.
Calculate the efficiency of an energy transfer or device using the formula `\text{efficiency} = \frac{\text{useful energy output}}{\text{total energy input}} \times 100`.
Classify energy resources as renewable or non-renewable and justify their classification.
Analyse and compare the environmental impacts of different energy resources using specific examples.

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