Energy and energy resources

• What is kinetic energy

  • energy stored in moving objects
  • Stationery objects have no kinetic energy
  • 0.5 x mass x velocity $^2$
• energy change as car moves

  chemical energy stored in petrol - kinetic energy store
• what is elastic potential energy

  • when we stretch a spring we’re applying a force to change the length of the spring
  • this is called “doing work”
  • the stretched spring is storing the energy needed to stretch it
• What is extension

  • The stretched spring from force added
  • Extension is directly proportional to force
• what is limit of proportionality

  when a springs extension is no longer directly proportional to extension
• what is gravitational potential energy

  • the energy stored in an object due to its position above the earths surface
  • Due to force of gravity
• gravitational potential energy equation

  mass x gravitational field strength x height
• what is specific heat capacity

  thr amount of energy required to raise the temperature of 1kg of the substance by 1 degree
• Specific heat capacity equation

  Change in thermal energy = mass x specific heat capacity x temp change
• what is thermal energy

  energy stored due to an objects temperature
• what is the law of the conservation of energy

  • energy can be transferred usefully, stored or dissipated
  • cannot be created or destroyed
• how does a pendulum show conservation of energy

  • it is a closed system - mass string and fixed point - no energy can enter of leave
  • maximum GPE at top of pendulum
  • GPE transferred to kinetic energy at bottom of swing - maximum kinetic energy
  • kinetic energy transferred to GPE as it moves up
• problem with pendulum

  • friction at fixed point and when the pendulum passes through air particles
  • friction causes energy to be transferred to thermal energy
  • fixed point and air gradually get warmer and less useful
  • DISSIPATED
  • causes pendulum to gradually slow down
• how do reduce unwanted energy transfer

  • reducing friction
  • using lubricant in fixed point
  • removing air particles
• conservation of energy in a bungee jumper

  • at the start of the jump, all the energy in the system is stored in the gravitational potential energy
  • as the jumper falls, energy is transferred from the gravitational potential energy store to the kinetic energy store
  • when the bungee rope starts to tighten the kinetic energy store is at its maximum
  • when the rope is fully extended the kinetic energy store is zero and the jumper is not moving
  • all energy has been transferred to elastic energy
  • bungee recoils and energy is transferred from elastic potential energy store back to the kinetic energy store
  • during ascent energy transfers from kinetic back to GPE
  • at the top of ascent all energy is in GPE
• key idea about bungee jumping

  • jumper never returns back to original position
  • energy is dissipated as thermal energy due to friction with air particles and stretching when the rope is not fully elastic
• What is work

  • Whenever energy is transferred from one store to another
  • Mechanical work involves using force to move an object
  • Electrical work uses current to transfer energy
• example of mechanical work

  • chemical energy store in dog
  • transferred to kinetic energy store in moving sledge
  • some kinetic energy is transferred to thermal energy stored in sledge and ground
• work done equation

  force x distance
• what happens when a car break

  • car is moving and has kinetic energy
  • break presses against wheel creating friction
  • kinetic energy of car is transferred to thermal energy in breaks
  • the temp in breaks increases slowing down the car to stationary
• what is power

  the rate at which energy is transferred or the rate at which work is done
• power equations

  Energy transferred/time

  Work done/time
• unit for power

  1 watt is an energy transfer (work done) of 1 joule per seconf
• efficiency equations

  Useful output energy transfer/total input energy transfer

  Useful power output/total power input
• how to increase efficiency in an electrical hob

  • want to increase thermal energy passing from hob to water
  • lots of energy is dissipated at edges not in contact with pan and thermal energy from the hot water
  • use an with wider base and a lid
  • reduce unwanted transfer of thermal energy
  • lots of energy is wasted heating the pan
  • place heating element inside water (kettle)
  • metal is a good heat conductor so energy passes through sides and lid into air
  • plastic has lower thermal conductivity so metals use plastic walls and lids
• what is thermal conductivity

  The higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across that material
• how are modern houses built

  • external brick and internal breeze block
  • between walls there is a cavity
  • high thermal conductivity
  • builder pack cavity with insulation with very low thermal conductivity
• therml energy and windows

  • single glaze has high thermal conductivity
  • double glaze has low thermal conductivity
• loft insulation

  low thermal conductivity
• how to reduce thermal energy transfer from a house

  using materials with low thermal conductivity

  build house with thick walls to reduce rate of thermal energy transfer
• Specific heat capacity practical

  1. place beaker on a balance and set to zero
  2. Add oil to beaker and record mass
  3. Place thermometer and immersion heater in oil
  4. Read starting temp
  5. Wrap beaker in insulating foam to reduce thermal energy transfer to surroundings
  6. Connect joulemeter to immersion heater
  7. Leave for 30 mins
  8. Read number of joules which passed into immersion heater and final temp of oil
  9. Calculate specific heat capacity
• sources of inaccuracy in specific heat capacity practicals

  • thermal energy passing out of beaker into air - use insulter with lower thermal conductivity
  • not all thermal energy passes into oil - ensure that immersion heater is fully submerged
  • incorrect reading of thermometer - use temperature probe
  • thermal energy may not be spread through oil - stir oil
• Uses of energy

  • transport
  • Generating electricity
  • Heating
• fossil fuels

  • coal
  • oil
  • gas
• advantages of fossil fuels

  • reliable
  • release a great deal of energy
  • abundant and relatively cheap
  • extremely versatile
• disadvantages of fossil fuels

  • burning fossil fuels releases huge amount of carbon dioxide
  • non-renewable - not replenished
  • Can release pollutants
• What is nuclear power

  Non re renewable - run on uranium and plutonium
• advantages of generating electricity through nuclear power

  • releases no carbon dioxide so doesn’t contribute to climate change
  • extremely reliable - a lot of electricity exactly when wanted
• disadvantages of nuclear power

  • contains highly dangerous radioactive materials
  • if there’s an accident these materials could be released in environment
  • decommissioning nuclear power plants takes many years and is expensive
  • produces large amounts of highly dangerous radioactive waste which must be stored for thousands of years before safe
• What is the uk energy mix

  • has an abundant reserve of coal
  • Nuclear power produced 20% of uk electricity by 1980s
  • In 1970s uk was major producer of coal and gas from North Sea
  • By 2000 as much electricity from burning gas and coal