The Energy topic covers conservation of energy, calculating kinetic and potential energy, work done and power, efficiency, and evaluating different energy resources for electricity generation.
Kinetic energy: KE = ½mv² (J). Gravitational potential energy: GPE = mgh (J). Work done: W = Fd (J) — force × distance in the direction of force. Power: P = W/t = E/t (W). Also P = Fv (force × velocity). Efficiency = useful output / total input × 100%. Conservation of energy: energy cannot be created or destroyed, only transferred. In falling object: GPE → KE (mgh = ½mv² gives v = √(2gh)).
Non-renewable: fossil fuels (coal, oil, gas) — reliable, high power, but CO₂ emissions; nuclear — no CO₂ during generation, radioactive waste, high decommissioning cost. Renewable: solar — no pollution, intermittent, large area; wind — no pollution, visual impact, intermittent; hydroelectric — reliable, limited locations, ecological impact; geothermal — constant, limited locations; tidal — reliable, expensive, limited locations; biomass — carbon neutral in theory, land use. Sankey diagrams: width of arrow proportional to energy, useful + wasted = total.
A Sankey diagram shows energy flow: the input arrow on the left splits into useful output (usually going right) and wasted energy (usually going down). The width of each arrow is proportional to the energy. Read the useful output value and the total input value from the diagram. Efficiency = (useful output / total input) × 100%. For example, if 400 J enters a motor and 100 J becomes useful kinetic energy while 300 J is wasted as heat: efficiency = (100/400) × 100% = 25%. The total of all output arrows must equal the input arrow (conservation of energy).
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