energy

• how can energy be transferred?


  heating

  waves

  electric current

  force
• what are the types of energy stores?

  1. chemical energy = fuels, foods or batteries. energy is transferred during these reactions.
  2. kinetic energy = the energy an object has when it is moving
  3. GPE = describes the energy stored in an object because of its position, such as an object above the ground
  4. elastic potential = describes the energy stored in a springy object when it is stretched or squashed
  5. thermal energy = the energy a substance stores because of its temperature
• how does energy transfer for a falling object?

  gravitational potential energy store decreases as energy is transferred to the kinetic energy store

  when it hits the ground, its kinetic energy store decreases as some of the energy is transferred to the environment through thermal energy or sound waves.
• what is a closed system?


  an isolated system in which no energy transfers take place out of or into the energy stores of the system. they have the same total energy before and after.

  however, energy can be transferred between energy stores within the system as long as the total energy is always the same.
• how does a bungee jump work?

  1. when rope is slack energy is transferred from GPE to KE as the jumper accelerates
  2. the rope tightens and the fall is slowed as the force of the rope reduces the speed of the jumper. KE store decreases and elastic potential increases as the rope stretches.
  3. the jumper stops and the energy from the KE store has been completely transferred to the elastic potential.
  4. some energy is lost to the thermal energy store
• how to work out values of different types of energies

  kinetic energy = 1/2mv^2

  elastic = 1/2ke^2

  GPE = mgh
• what is work? 


  energy transferred = work done

  when an object is moved by force, work is done on the object and the force transfers energy to the object.

  work done = force x distance
• what is useful energy?


  useful energy is energy that is transferred to where it is wanted

  wasted energy is the energy that is not usefully transferred

  wasted energy often dissipates ro the surroundings
• work is done when energy is transferred from one store to another and the amount of energy transferred depends on the size of the force and the distance the force moves
• work done = force x distance
• mass vs weight


  the mass of a body tells us how much matter it contains, measured in Kg.

  the weight of the body is the force that acts on it due to gravity measure in newtons - weight = mass x g
• kinetic energy 


  kinetic energy is the energy a body posses because its in motion depending on mass and speed

  KE = 1/2mv^2
• energy becomes less useful the more it dissipates
• what is efficiency?


  efficiency is a measure of how well a device converts input energy into output energy.

  efficiency percentage = useful energy output/total energy input x 100
• why do devices waste energy ?

  1. friction between moving parts causes heating
  2. resistance of a wire causes wire to heathen current is passed through
  3. air resistance opposes motion and energy transferred is wasted to the surroundings
  4. sound created by machinery
• how do we reduce wasted energy?

  1. lubricate moving parts to reduce friction
  2. in circuits use wires with little electrical resistance
  3. make moving objects streamlined
  4. cut out noise from machinery
• energy cannot be created or destroyed, only transferred from one store to another
• resolution is the smallest measure that an instrument can measure
• energy = power x time
• how is energy transferred by conduction?

  as heat is a form of energy, heat is transferred in solids by conduction as thermal energy always flows from hot to cold.
• when heat is transferred to an object it's temp increase depends upon the mass of the object, the amount of energy transferred and the substance that the object is made from.
• what is the specific heat capacity of a substance?

  the specific heat capacity of a substance is the amount of energy required to raise the temp of one kilogram of the substance by one degree celsius.

  change in energy = mass x specific heat capacity x change in temp
• the energy transfer per second through a layer of insulating material depends on

  the temperature difference across the material

  the thickness of the material

  the thermal conductivity of the material.
• building insulation 


  loft insulation - matting that traps air pockets

  double glazing - two panels of glass with air between

  cavity wall insulation - foam trapping air pockets

  doors - have draught excluders to stop air escaping

  aliminium foil - reflects heat back into room
• greenhouse effect 


  1. short wavelength infrared passes through atmosphere
  2. earth absorbs infra-red
  3. earth emits long wavelength infra-red
  4. atmosphere absorbs infra-red
  5. atmosphere re-emits infra-red
• greenhouse effect summary


  the earths surface emits infra-red radiation with a long wavelength because the temperature of the earth is colder than the temperature of the sun.

  greenhouse gases, such as carbon dioxide, absorb this longer wavelength radiation and re-emits it back to the ground. this makes the earth hotter than it would be if the atmosphere did not contain greenhouse gases.
• a renewable energy resource is one that can easily or quickly be replenished

  a non-renewable source of energy is one that cannot be easily or quickly replenished.
• renewable energy sources


  wind

  solar

  wave

  hydroelectric

  geothermal

  tidal

  biomass
• non-renewable


  oil

  coal

  natural gas

  nuclear
• coal oil and natural gas are fossil fuels. they were all formed as a result of dead plants or animals being subjected to heat and pressure under the ground
• we transform chemical energy in fossil fuels into thermal energy by burning them. the thermal energy may be used to heat a building or transformed into kinetic energy .

  in a power station, the turbine would drive a generator, converting kinetic energy into electrical energy.
• carbon dioxide absorbs heat energy and prevents it escaping from the earths atmosphere into space. the greater the amount of carbon dioxide in the atmosphere, the more heat energy is absorbed and the earth gets hotter.
• uranium or plutonium is used to power nuclear power stations as they release much more energy per kilogram than fossil fuels
• conduction is the process where vibrating particles transfer energy to neighbouring places.

  convection is where energetic particles move away from hotter to cooler regions.
• convection can happen in gases and liquids. energy is transferred by heating to the thermal store of the liquid or gas.

  the particles are able to move so the space between individual particles increases. this causes density of the region being heated to decrease.

  the warmer and less dense region will rise above the denser, cooler regions.

  if there is a constant heat source, a convection current can be created
• conduction happens mainly in solids. energy transferred to n object by heating goes to the thermal store of the object. this energy is shared across the kinetic stores of the particles in the object.

  particles vibrate and collide

  collisions cause an energy transfer
• wind power


  1. turbines have generators to produce electricity form the rotating blades
  2. no pollution
  3. wind turbines stop when there s no wind. only work 75% of the time
  4. costs are high
  5. no permanent damage to landscape
• solar panels


  1. best source to charge batteries
  2. used in remote places
  3. no pollution
  4. reliable
  5. initial cost is high
  6. requires sun
  7. small scale generator
• geothermal power


  1. only possible in volcanic areas produced by the slow decay of radioactive elements in the earth
  2. free
  3. generates electricity or heat buildings
  4. not many suitable locations for power plants. cost is too high for the amount of energy produced
• hydroelectric power 


  1. requires flooding of s valley by building a dam
  2. no pollution
  3. impact on environment due to flooding of valley and loss of habitat
  4. immediately responds to demand for electricity
  5. initial cost high, but no running cost
  6. generates electricity on a small scale in remote areas.