energy

• kinetic energy (J) = 0.5 x mass (Kg) x speed2 (m/s)
• hooke’s law the extension of a spring I’d directly proportional to the force applied, provided that the limit of proportionality is not exceeded
• limit of proportionality - when the spring stops obeying hooke’s law
• gravitational energy is the energy stored in an object due to its position above the earth’s surface due to the force of gravity acting upon an object
• gravitational potential energy = mass (Kg) x gravitational field strength (N/Kg) x height (m)
• the law if conservation of energy

  energy can be transferred usefully, stored, or dissipated but it cannot be created or destroyed
• energy transfers: pendulum

  • at the top the mass has the maximum store of GPE
  • as the pendulum swings this is transferred to the kinetic energy store
  • the mass has the maximum kinetic energy store at the bottom of the swing (its moving at the fastest speed)
  • as the mass swings back up the kinetic energy store transfers to the GPE store again
• friction is caused in the fired point of the pendulum as well as the pendulum
• friction in the fixed point of the pendulum as well as the pendulum passing through air particles. friction causes energy to be transferred to thermal energy. the fixed point and the air around the pendulum gradually get warmer, but these stores of thermal energy are less useful as the energy has been dissipated (wasted) this will cause the pendulum to gradually stop swinging with less energy and then stop.
• we can reduce unwanted energy transfers by reducing friction

  • use a lubricant (oil on the fixed point)
  • remove the air particles from around the pendulum
• Energy transfers: bungee jump

  1. At the start of the jump, all the energy in the system is the store of gravitational potential energy

  2. As the jumper falls, energy is transferred from the gravitational potential energy store to the kinetic energy store

  3. When the bungee rope just starts to tighten, the kinetic energy store is at its maximum

  4. When the rope is fully extended, the kinetic energy store is zero as the jumper is not moving

  5. All of the energy has been transferred to the elastic potential energy store

  6. The bungee rope now recoils and energy is transferred from the elastic potential energy store back to the kinetic energy store

  7. During the ascent, energy transfers back from the kinetic energy store back to the potential energy store

  8. Finally at the top of the ascent, all of the energy is now in the gravitational potential energy store
• the jumper never returns back to the same position because energy is dissipated as the thermal energy due to friction with air particles and stretching effects in the bungee rope which is not fully elastic
• work is done when energy is transferred from one place to the other
• mechanical work involves using a force to move an object
• electrical work involves a current transferring energy
• work done (J) = force (N) x distance (m)
• power is the rate at which energy is transferred or the rate at which work is done
• power (W) = energy transferred (J) / time (s)
• power (W) = work done (J) / time (s)
• efficiency = useful output energy transfer / total input energy
• efficiency = useful power output / total power input
• increasing efficiency

  • use a pan with a wider base
  • use a lid
  • overcome the fact that a lot of thermal energy is actually used to heat the base of the pan itself by placing the heating element inside the water
  • metal is a good conductor of heat so thermal energy will pass through the sides and into their so better to use a kettle with plastic calls and lid
• higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across that material
• uses of energy

  • transfer
  • generating electricity
  • heating
• modern houses are made from two layers

  • external brick
  • internal breezeblock wall
  • between walls there is a cavity where builders pack insulating materials which has a very low thermal conductivity
• single-glazed: high thermal conductivity

  double-glazed: low thermal conductivity
• loft insulation in roofs reduce the rate at which thermal energy passes through as it has low thermal conductivity
• fossil fuel advantages

  • reliable (they always provide energy when we need it)
  • release a great deal of energy
  • abundant
  • relatively cheap
  • extremely versatile
• fossil fuel disadvantages

  • burning fossil fuels releases huge amounts of carbon dioxides
  • non-renewable as they are not being replenished as we use them
  • burnin fossils fuels can release other pollutants (diesel produces carbon particles and nitrogen oxides, coal produces soulful dioxide which leads to acid rain damaging buildings and trees)
• nuclear power is non-renewable. nuclear power plants run on the elements of uranium and plutonium
• advantages of nuclear power

  • once a nuclear power plant is running it releases no carbon dioxide
  • extremely reliable (generate a lot of electricity when we want it)
• disadvantages of nuclear power

  • contain highly dangerous radioactive materials so if there’s an accident the materials could be released into the environment
  • decommissioning a nuclear power plant takes many years and is very expensive
  • nuclear power plants generate large amounts of highly dangerous radioactive waste (this must be stored for thousands of years before its safe)
• the uk had an abundant reserves of coal, up until the 1950s almost all of the electricity generated in the uk came from coal. in the 1950s nuclear power came online and by the 1980s this produced around 20% of all of the UK’s electricity
• in the 1970s the UK became a major producer of oil and gas from the north sea and began to replace coal for generating electricity. by 2000 as much electricity was generated from gas from burning coal.
• switching from coal to gas

  • burning gas generates less carbon dioxide then burning coal, this contributes less to climate change
  • gas-fired power stations are flexible, they can be switched on quickly during periods of high demand (short start-up time)
• in the 1970s, scientists began to realise that carbon dioxide emissions from human activity could be leading to climate change. At the time, politicians did not really see that as a big issue. Energy from fossil fuels was very cheap. This is an economic factor. Switching away from fossil fuels costs money and that could cost jobs.
• The UK has got one of the best locations for wind power in the world. Over the last decade, the UK has opened a large number of wind-farms.
• The future of UK energy

  • we need a baseload (a constant supply of electricity that’s on all the time), nuclear power is ideal for this
  • we can use gas-fired power stations to provide emergency power in times of peak demand
  • renewables will provide the bulk of our electricity, with nuclear providing a base load and then gas providing electricity during periods of peak demand
• renewable energy resource is one that is being replenished as it is used
• renewable energy resources

  • tidal power
  • biofuels
  • geothermal
  • wave power
  • solar power
  • hydroelectricity
  • wind power