P4 - Energy

• Gravitational potential energy

  mass (kg) x gravity (n/kg) x height (m)
• Kinetic energy

  1/2 x mass (kg) x velocity^2
• Efficiency (% or decimal)


  useful energy / total energy
• Power


  work done (J) / time (s)
• Work done


  Force x distance
• Moment of a force (Nm)

  Force (N) x distance (m)
• Cras kinetic energy store = work done by brakes


  1/2 x m x v^2 = f x d
• Conservation of Energy

  Energy cannot be created or destroyed it can only be transferred from one store to another
• Energy stored in food, fuel and batteries is chemical energy
• Energy stored in moving objects is kinetic energy
• Energy stored in hot objects is thermal energy
• Energy stored in stretched or squashed or twisted materials is elastic potential energy
• Energy stored in objects in high positions is gravitational potential energy
• Energy stored inside atoms is atomic or nuclear energy
• If object is projected into the air

  As it rises

  • higher kinetic energy will be changed into gravitational potential energy
• Demand for energy 


  
  

  • Varies with the time of year and the time of day

  During early evenings

  • a lot of energy is needed for heating, lighting and cooking

  Overnight

  • very little needed while people sleep
• Water waves energy


  • Renewable
  • Has low power output
  • Very little impact
• Solar energy


  • Renewable
  • Potential of very high power output
  • Very little impact
• Geothermal energy


  • Renewable
  • Has medium power output
  • Very low impact on the earth
• Hydroelectric


  • Renewable
  • Has medium power output
  • Local habitats are affected by the dams built
• Wind energy 


  • Renewable
  • Has very low power output
  • Take large amount of space up
• Bio-fuels 


  • Renewable
  • Have medium power output
  • Have low impact
• Nuclear fuels


  • Non renewable
  • Have very high power output
  • Release radioactive waste
• Fossil fuels 


  • Non-renewable
  • Have high power output
  • Release CO2
• Renewable energy


  Resource is one that is being replenished as fast as it is used
• A moving object will start off with kinetic energy...


  
  

  Once it hits obstacle

  • kinetic transferred to surroundings
  • as thermal energy and sound waves

  Some of kinetic energy of moving object can be transferred to obstacle

  • causing it to move
• When an object is accelerated by a force


  • transfer of energy

  Energy is required to accelerate the object

  • could be chemical, thermal or electrical

  This energy when converted into kinetic energy 

  • used to accelerate the object
• To slow down the vehicle


  
  

  • the kinetic energy of the movement will be transferred into another store of energy
  • could be sound waves and thermal energy.
• When we are heating up water in an electric kettle


  
  

  • transferring electrical energy into thermal energy
  • used to heat up the water
• Where there are energy transfers in a closed system 


  
  

  • no net change to the total energy in that system
• Open systems


   Able to exchange energy and matter with their surroundings
• Closed system 


  Unable to exchange energy and matter with their surroundings
• Mechanical processes


  • Become wasteful when they cause a rise in temperature
  • Dissipating energy in heating the surroundings
• Releasing energy from some stores

  • Causes pollution and harmful waste products

  Burning fossil fuels

  • releases carbon dioxide
  • adding to the greenhouse effect
  • sulphur dioxide which causes acid rain
• When two moving parts touch

  • friction causes them to heat up

  This thermal energy is wasted

  • this can be reduced using lubrication
• Insulation


  Slows down the rate at which energy is transferred out of a house by heating
• The rate of energy transfer is reduced 


  • Increasing thickness
  • Decreasing thermal conductivity

  This means that it takes longer for the building to cool
• Efficiency = useful energy/total energy supplied
• Efficiency can be increased by reducing wasted energy transfers so more of the input energy is usefully transferred
• Main energy sources

  • Fossil fuels
  • Nuclear fuel
  • Bio-fuel
  • Wind
  • Hydroelectric
  • Tidal
  • Solar
  • Geothermal