P7

• energy stores

  • Kinetic- moving has energy in its kinetic store
  • Thermal- the hotter the more energy
  • Chemical- release energy by chemical reaction
  • Gravitational potential- anything in a gravitational field
  • Elastic potential- anything stretched
  • Electrostatic- two charges attract or repel
  • Magnetic- two magnets attract or repel
  • Nuclear- atomic nuclei release energy from store in nuclear reaction
• Transferred between stores

  • Mechanically- moving due to force
  • electrically- charge moving through potential difference
  • by heating- energy transferred from a hotter object to a colder object
  • by radiation- energy transferred by light/sound waves
• Law of conservation of energy

  • energy can be store, transferred between stores and dissipated- but can never be created or destroyed
• Energy s only useful when transferred from one store to a useful store
• efficiency= useful output energy transfer (J) / input energy transfer (J)
• Energy transferred by heating

  • energy is transferred to its thermal energy store and its temperature increases
  • hotter temp to cooler- hotter temp decreases and cooler increases
• Conduction

  • process where vibrating particles pass extra energy in their energy stores to kinetic stores to their neighbouring particles
  • occurs mainly in solids- particles closest together
  • energy transferred to the object is shared across the kinetic energy store of the particles
  • particles in the hotter region vibrate more and collide with each other - transferring their kinetic energy
  • Vibrating increases the temperature
  • Continues until the temperature is the same everywhere
• Convection

  • particles with more energy in their kinetic energy store move from a hotter region to a cooler region and take their kinetic energy stores with them
  • to reduce convection- stop the fluid from moving
  • air can't move so energy has to conduct slower
• Radiation

  • travel through a vacuum
  • energy is transferred by heating by radiation- carried by infra-red waves
  • All objects absorb the radiation - the hotter the object the more radiation
  • cooler objects absorb the radiation from hotter things
  • Marr black surfaces are good absorbers
  • Light-coloured, smooth and shiny objects are poor absorbers
• Insulating house to reduce unwanted energy transfers

  • Loft insulating- fibreglass 'wool' laid on the floor and ceiling reduces energy loss from the house by conduction and convection
  • Cavity walls and Cavity wall insulation- two layers of bricks with a gap between them reduce conduction - insulating foam un gap to minimise convection
  • Double glazing- two layers of glass with an air gap to reduce conduction
  • Thick curtains- reduce heat loss by convection and conduction
  • Draught-proofing - strops of foam and plastic around doors and windows stop air going out- reducing convection
• Energy loss rom water pipes

  • reduced by
  • Covering pipes with insulation to reduce conduction and convection
  • paining the pipes white to reduce energy loss by radiation
  • making pipes as short as possible, so water spends less time in pipes
  • making pipes wide so smaller surface area to volume ratio
• Reducing friction

  • leads to energy being lost through heating
  • reduced with lubrication
• electrical circuits

  • device connected to mains
  • energy is transferred electrically from the mains to the device
  • a battery has energy in chemical stores
  • Energy transferred to the kinetic energy store of the motor
  • energy is transferred to the thermal energy store of the kettle's heating element
  • energy is carried away from the speaker by sound waves
  • energy is carried away from the bulb in light waves
  • some every is wasted
  • transferred to thermal heating which is waste