Energy

• ENERGY: Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed.
• An Object Projected Upwards:

  • Before the ball is thrown upwards, the person holding the ball has a store of chemical energy
  • When the ball is thrown, some of that energy is transferred to the kinetic store when it move upwards
  • As the height of the ball increases, energy from the kinetic store of the ball is transferred to its gravitational potential store

  
• A Moving Object Hitting an Obstacle

  • Fuel contains chemical energy.
  • When the car moves, this chemical energy changes into kinetic energy.
  • When the car hits the wall, its kinetic energy quickly decreases.
  • Most of this kinetic energy is converted into thermal energy in the car, the wall, and the air.
  • Some energy is also transferred as sound energy, making the air vibrate.

  
• A Vehicle Being Accelerated by a Constant Force

  • When a vehicle is stationary, it has energy in the chemical store of the fuel
  • When the vehicle speeds up or accelerates, the energy is transferred to the kinetic store of the car

  
• A Vehicle Slowing Down

  • When a vehicle is moving, it has kinetic energy.
  • As the vehicle slows down, this kinetic energy is transferred to the thermal store of the surroundings.
  • This energy is transferred as heat due to friction between the tyres and the ground, and between the brakes and brake pads.
  • Some energy is also transferred as sound energy, making the air particles vibrate

  
• Boiling Water in a Kettle

  
  

  Electricity through the kettle increases the internal energy of the element which in turn increases the internal (thermal) energy of the water which increases the temperature of the water

  Plastic walls and lid have a low thermal conductivity making it more efficient

  
• TYPES OF ENERGY:

  • magnetic
  • internal (thermal)
  • chemical
  • kinetic
  • electrostatic
  • elastic potential
  • gravitational potential
  • nuclear
• Kinetic energy is transferred into gravitational potential energy

  
• TYPES OF ENERGY TRANSFER:

  • mechanical work - a force moving an object through a distance
  • electrical work - charges moving due to a potential difference
  • heating - due to temperature difference caused electrically or by chemical reaction
  • radiation - energy transferred as a wave, eg light and infrared - light radiation and infrared radiation are emitted from the sun
• DISSIPATION:

  Energy is let out to the surroundings
• KNETIC ENERGY: Kinetic energy is energy in a moving object

  equation: Ek = 0.5 X mass X (speed)^2

  Ek = 1/2 x m x v^2

  Ek-(J)

  m-(kg)

  v-(m/s)
• GRAVITATIONAL POTENTIAL ENERGY: The amount of gravitational potential energy gained by an object raised above ground level

  equation: g . p . e = mass X gravitational field strength X height

  Ep = m x g x h

  m-(kg)

  g-(N/kg)

  h-(m)

  earth=9.8(N/kg)
• ELASTIC POTENTIAL ENERGY: The amount of elastic potential energy stored in a stretched spring

  equation: Ee =0.5 X spring constant X (extension)^2

  Ee = 1/2 x k x e^2

  Ee-(J)

  k-(N/m)

   e-(m)
• ENERGY: The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.

  Equation: change in thermal energy = mass × specific heat capacity × temperature change

  ∆E = m c ∆θ

  ∆E-(J)

  m-(kg)

  c-(J/kg °C)

  ∆θ-(°C)
• (1)EFFICIENCY: equation: efficiency = useful output energy transfer/total input energy transfer

  and

  efficiency = useful power output/total power input

  if to a percentage: X 100%

  usually in joules
• (1)POWER: Power is the rate in which energy is transferred/work is done

  P = E/t 

  power = energy transferred/time

  P = W/t

  power = work done/Time

  P-(W)

   E-(J)

  t-(s)

  W-(J)

  1 joule per second = power of 1 watt.
• The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material.
• work done is when energy is transferred from one store to another

  work done = force × distance

  W=F×d

  This is when:

  • work done (W) is measured in joules (J)
  • force (F) is measured in newtons (N)
  • distance (d) is in the same direction as the force and is measured in metres (m)
• When trying to keep houses warm, the choice is between materials that are poor conductors such as brick, wood, plastic and glass. A house built of conducting materials like copper would be very cold to live in as energy would be able to leave the house easily.

  examples

  loft insulation

  double glazed windows
• To reduce thermal energy transferred from a warm house, the walls can be built thicker, Thermal energy transfers can be reduced further if there are two walls with an air gap between them, as air has a lower thermal conductivity than brick. This is known as a 'cavity wall'.

  The cavity is packed with an insulating material to reduce the thermal conductivity of the walls
• A building with walls of a high thermal conductivity will cool down faster than one with walls of a low thermal conductivity
• WAYS TO INCREASE EFFICIENCY:

  • Lubricants/oil - less friction
  • insulation - less heat transfer
  • streamlining - shape reduces air resistance
• as a metal is heated the kinetic energy of the atoms increase and the thermal energy also increases.
• energy is dissipated to the surroundings at the same rate that energy is transferred to the water

  Questions where there is no change eg
• FOSSIL FUELS: Energy resource: Fossil fuels (oil,coal,natural gases)

  Energy store: Chemical

  Renewable? Non-renewable

  Uses: Transport, heating, electricity generation

  Power output: High

  Environmental impact:

  Releases CO2 (causes global warming)
• NUCLEAR FUELS: Energy resource: Nuclear fuels

  Energy store: Nuclear

  Renewable? Non-renewable

  Uses: Electricity generation

  Power output: Very high

  Environmental impact:

  Radioactive waste (needs to be disposed of safely)
• BIO-FUEL: Energy resource: Bio-fuel

  Energy store: Chemical

  Renewable? Renewable

  Uses: Transport, heating, electricity generation

  Power output: Medium

  Environmental impact:

  'Carbon neutral', so low impact
• WIND: Energy resource: Wind

  Energy store: Kinetic

  Renewable? Renewable

  Uses: Electricity generation

  Power output: Very low

  Environmental impact:

  Takes up large areas that could be used for farming, some people say windmills spoil the view
• HYDROELECTRICITY: Energy resource: Hydroelectricity

  Energy store: Gravitational potential

  Renewable? Renewable

  Uses: Electricity generation

  Power output: Medium

  Environmental impact:

  Local habitats are affected by the large areas that need to be flooded to build dams
• GEOTHERMAL: Energy resource: Geothermal

  Energy store: Internal (thermal)

  Renewable? Renewable

  Uses: Electricity generation, heating

  Power output: Medium

  Environmental impact: Very low
• TIDES: Energy resource: Tides

  Energy store: Kinetic

  Renewable? Renewable

  Uses: Electricity generation

  Power output: Potentially very high, but hard to harness

  Environmental impact:

  Tidal barrages can block sewage which needs to go out to sea
• SUN: Energy resource: Sun

  Energy store: Nuclear

  Renewable? Renewable

  Uses: Electricity generation, heating

  Power output: Dependent on the weather and only available during daylight

  Environmental impact: Very little
• WATER WAVES: Energy resource: Water waves

  Energy store: Kinetic

  Renewable? Renewable

  Uses: Electricity generation

  Power output: Low

  Environmental impact: Very low
• Power stations that use fossil fuels or nuclear fuel are very reliable sources of energy and operate continuously. The fuel for nuclear power stations is cheap but power stations are expensive to build/dismantle. highly radioactive waste is stored for millions of years before the natural activity will reduce to a safe level.

  Water power-tidal and hydroelectricity is reliable and predictable because the Moon causes the tides and rainfall filling reservoirs. sunny and windy weather cannot be guaranteed
• A renewable energy resource is one that is being (or can be) replenished as it is used.
• ENERGY TRANSFERS: PENDULUM

  Max GPE at the top of the pendulum.

  as it goes down GPE decreases and KE increases

  KE decreases then GPE increases at the top of the pendulum.

  At the fixed point there is friction and the air particles turn into thermal energy which makes the energy dissipated.

  we can use lubricant on the fixed point or remove the air particles.
• ENERGY TRANSFERS: BUNGEE JUMPER

  At the top jumper has a store of GPE

  as they fall KE increases and GPE decreases

  when the rope tightens its at the max KE

  When extended KE is at zero

  KE->EPE

  EPE->KE as it loosens

  as it goes back up and GPE increases

  
  

  Thermal energy dissipates so they will never return to their original position
• FOSSIL FUELS ADVANTAGES/DISADVANTAGES:

  • reliable
  • release a great deal of energy
  • abundant and cheap
  • versatile
  • releases carbon dioxide
  • non-renewable
  • release other pollutants like sulphur dioxide
• NUCLEAR POWER: ADVANTGES/DISADVANTAGES

  • Non-renewable
  • no carbon dioxide
  • reliable
  • highly dangerous material
  • many years and expensive
• UK ENERGY MIX:

  Switch from coal to gas:

  • less carbon dioxide
  • flexible (short start up time)
  • Switch to renewables:
  • scientists realised carbon dioxide is leading to climate change
  • energy to fossil fuels was very cheap
  • UK has wind-farms and best location for it
  • Future of UK energy:

  a constant energy is needed nuclear power is ideal for it

  Renewables will provide bulk electricity as well as gas and nuclear

  
  

  When using more efficient methods there is less energy demands as they use less energy