Topic 2 - Conservation of Energy

• energy transferred between energy stores

  kinetic - anything moving has energy stored here

  thermal - any object, the hotter it is the more energy it has here

  chemical - anything that can release energy by a chemical reaction

  gravitational potential - anything in gravitational field (that can fall)

  elastic potential - anything stretched

  electrostatic - e.g. two charges that attract or repel each other

  magnetic - e.g. two magnets that attract or repel each other

  nuclear - atomic nuclei release energy from here during nuclear reactions
• a moving object has energy in its kinetic energy store

  energy transferred to this store if an object speeds up - away from store if it slows down

  how much energy is in this store depends on both the objects mass and speed

  greater the mass = faster its going = more energy it has in its store

  kinetic energy = 0.5 X mass X speed (KE=1/2mv$^2$)

  if you double mass - energy in store doubles

  if you double speed - energy in store quadruples
• a raised object has energy in its gravitational potential store

  $\Delta$GPE = mg$\Delta$h

  change in gravitational potential energy = mass X gravitational field strength X change in vertical height
• conservation of energy - energy is never created or destroyed


  'energy can be stored, transferred between stores, and dissipated but can never be created or destroyed - total energy of a closed system has no net change'
• closed system

  a system (collection of objects) that can be treated completely on its own and where there is no net change in systems total energy

  if question about where energy of an object increases/decreases - not a closed system

  can make it a closed system by increasing the number of things you treat as part of it (e.g. pan of water heating on a hob isnt a closed system - the pan, gas and oxygen that burn to heat it, surroundings is)
• 4 main ways of transferring energy

  mechanically - force acting on object (and doing work) e.g. pushing

  electrically - a charge doing work

  by heating - energy transferred from hotter object to cooler

  by radiation - energy transferred by waves
• 'energy is only useful when it is transferred from one store to a useful store'


  however - some of the input energy is always dissipated or wasted, often to thermal energy stores of its surroundings

  whenever work is done mechanically - frictional forces have to be overcome, including things like moving parts rubbing together and air resistance - energy needed to overcome these is transferred to the thermal energy stores of whatevers doing the work and the surroundings

  energy usually isnt useful and is quickly dissipated
• conservation of energy principle

  total energy input = useful energy output + wasted energy

  the less energy thats wasted - the more efficient the device is said to be

  the amount of energy that is wasted can often be reduced
• efficiency

  = useful energy transferred by device / total energy supplied to device

  all devices have an efficiency, but because some energy is always wasted, the efficiency can never be equal to or higher than 1 (100%)
• lubrication decreases energy transferred by friction

  whenever something moves theres usually at least one frictional force acting against it

  this transfers energy mechanically (work done against friction) to the thermal energy store of the objects involved, which is then dissipated by heating to the surroundings

  for objects that are touching each other - lubricants can be used to reduce the friction between the objects' surfaces when they move

  usually liquids (like oil) so they can flow easily between objects and coat them
• insulation reduces rate of energy transfer by heating

  when one side of an object is heated - particles in the hotter part vibrate more and collide with each other - transfers energy from their kinetic energy stores to other particles (which then vibrate faster)

  this process called conduction - it transfers energy through the object

  all materials have thermal conductivity

  in building - the lower the thermal conductivity of the walls, the slower the rate of energy transfer between them
• what can be done in buildings to help with energy transfer

  cavity walls

  • made up of inner and outer wall with air gap in the middle
  • air gap reduces amount of energy transferred by conduction (air has very low thermal conductivity)

  thicker walls

  • the thicker the wall - the slower the rate of energy transfer
• non-renewable energy sources - positives

  • fossil fuels and nuclear energy are reliable - still plenty of fuel around to meet current demand (power plants always have fuel in stock) - means they can respond quickly to changes in energy demand
  • cost to extract fuels is low - fossil power plants are relatively cheap to build and run
• non-renewable energy sources - negatives

  • nuclear power plants are costly to build / safely decommission

  create environmental problems

  • fossil fuels release carbon dioxide - adds to greenhouse effect
  • burning coal/oil can release sulfur dioxide which causes acid rain - can be reduced by taking sulfur out before fuel is burned
  • oil spillages - effect mammals and birds that live around sea
  • nuclear waste very dangerous and difficult to dispose of - theres always a risk of a major catastrophe
• renewable energy sources

  bio-fuels

  wind

  solar power

  hydro-electric power

  tides

  • they will never run out
  • most do damage environment but less than non-renewables
  • dont provide as much energy
  • some are unreliable - depend on the weather
• bio-fuels

  created from plant products/animal dung

  can be solid/liquid/gas and burnt to produce electricity

  supposedly carbon neutral - only true if you keep growing plants/animals at the rate your burning things

  fairly reliable - crops take short time to grow/grown all year round

  cant respond to immediate energy demands

  to combat - continuously produced and stored for when needed

  cost to refine is very high

  worry that growing crops for this means there isnt enough space/water to meet demands for crops grown for food
• wind power

  each wind turbine has generator inside - wind rotates the blades which turn generator and produce electricity (no pollution)

  initial costs high - running costs minimal

  lots of them needed to produce enough power

  can spoil view and be noisy

  only work when windy - cant always supply electricity / respond to high demand
• solar cells

  made from materials that use energy transferred by light to create electrical current

  often used in remote places where theres not much choice / to power electric road signs and satellites

  no pollution

  initial costs high - practically no running costs

  mainly used to generate small-scale electricty

  most suitable for sunny countries

  cant increase power at night / increase production when extra demand
• hydro-electricity

  involves flooding a valley by building a dam - rainwater caught and allowed out through turbines

  no pollution

  big impact on environment due to flooding - possible loss of habitat

  can immediately respond to increased electricity demand - more water can be let through turbines

  initial costs high - minimal running costs

  generally reliable
• tidal barrages

  big dams built across river estuaries with turbines in them

  as tide comes it fills up estuary - water then let out through turbines at controlled speed

  no pollution

  affect boat access

  can spoil view

  alter habitat for wildlife

  pretty reliable (tides happen twice a day) - but height of tides is variable and barrages dont work when watter level is same either side

  initial costs moderately high - minimal running costs / no fuel costs
• currently...

  over 20th century - electricity use of UK hugely increased (population got bigger - more demand)

  since beginning of 21st century - electricity use in UK has been slowly decreasing - getting better at making more efficient appliances

  electricity - fossil fuels and nuclear power / renewables

  burn fossil fuels - oil to fuel cars / gas to heat homes and cook (renewable energy sources can be used for these as well)

  we are trying to increase our use of renewable energy sources
• energy resources chosen for their effect on the environment

  burning fossil fuels - negative effect - people want renewables that have less of an effect on the environment

  pressure from other countries and pubilc - govs began to introduce targets for using renewables - in turn puts pressure on energy providers to build new power plants that use renewables (makes sure they dont lose business/money)

  car companies - demand for electric cars gradually increasing
• use of renewables limited

  building renewable power plants costs money - some smaller energy providers reluctant to do this

  if new power plants built - arguments on where they should be

  some not as reliable / cant increase their power output on demand - have to use combinations of different power plants (expensive) / researching ways to improve reliability

  research / improving reliability take time and money - could take years before improvements made

  personal changes - expensive/impractical - e.g. solar panels for homes = expensive, electric cars - charged = hard in rural areas