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p7 (conservation (energy is transferred between energy stores, kinetic :…
p7
conservation
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thermal : any object - the hotter it is, the more energy in its store
chemical : anything that can release energy by a chemical reaction eg food, fuels
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conduction
mainly in solids, when an object is heated, energy transferred to the object is shared across the kinetic energy stores of the particles in the object
particles in hotter part vibrate more and collide with each other, transfer energy from kinetic energy store to neighbouring particles, also vibrate faster, increase temp of that part of the object
continues until extra energy is spread out evenly across all particles, temp of the object is same everywhere
conduction is the process where vibrating particles pass extra energy in their kinetic energy stores to the kinetic energy stores of neighbouring particles
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all objects have thermal conductivity, how well an object transfers energy by conduction
metal has high thermal conductivity, liquids and gases have a low thermal conductivity
efficiency
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some input energy is always lost or wasted, often to thermal energy stores by heating
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less energy wasted, more efficient the device
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convection
heat up a liquid or gas, particles move faster and the fluid expands, becomes less dense
warmer, less dense fluid rises about its colder, denser surroundings
as warm fluid rises, cooler fluid takes its place, process continues until a circulation of fluid (convection currents)
convection occurs when the particles with more energy in their kinetic energy stores move from the hotter region to the cooler region, and take their kinetic energy stores with them
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to reduce convection, fluid needs to stop moving. foam cavity wall insulation work by trapping pockets of air. air can't move so the energy has to conduct very slowly through the pockets of air, as well as the material in between.
transferring energy
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mechanically : object moving due to a force acting on it eg pushing, pulling, stretching, squashing
electrically : a charge moving through a potential difference, eg charges moving round a circuit
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by radiation : energy transferred eg by light/sound waves eg energy from the sub reaching the earth by light
radiation
energy can be transferred by radiation, not just particles, can travel through a vacuum
energy transferred by heating by radiation, will be carried by infra-red waves
all objects emit and absorb radiation, hotter and object gets, more radiation it emits
cooler objects absorb the radiation emitted by hotter things, so temp increases
matt black are good absorbers and emitters of radiation, whereas light coloured smooth and shiny objects are poor absorbers and emitters
wasted energy
transferred to less useful stores, normally heating, light or sound
as energy is transferred, it often spreads out and becomes less concentrated - dissipates
law
energy can be stored, transferred between stores and dissipated, but it can never be created or destroyed. the total energy of a closed system has no net charge
heating
conduction, convection or radiation