Conservation of Energy

• SI units for gravitational potential energy


  Energy (J), Mass(kg), Gravitational Field Strength (N/kg), Height (m)
• Kinetic energy equation


  ½ m v2
• SI units for kinetic energy


  Energy (J), Mass(kg), Velocity(m/s)
• Conservation of energy


  • The total amount of energy in a closed system remains constant
  • Energy cannot be made or destroyed but can change from one form to another
• Energy changes when a ball is thrown upwards and returns to starting position


  1. Upwards: KE is converted to GPE

  2. Peak: Maximum GPE, zero KE

  3. Downwards: GPE is converted to KE
• The total energy of a kicked ball remains constant due to conservation of energy
• Energy changes in a filament light-bulb


  1. Electrical energy is transferred into light and heat energy

  2. Light is a useful energy form, heat is waste energy
• Energy transfers for a bungee jumper

  1. When falling, the GPE is converted to KE of jumper

  2. As the cord tightens, KE is converted and stored as Elastic Potential Energy (EPE)

  3. At lowest point, the jumper's initial GPE equals the EPE stored in the cord
• Bungee jumper slows down once the cord begins to stretch

  • Kinetic energy decreases since it is converted to elastic potential energy
  • Since KE is proportional to (velocity)², as KE decreases, so does velocity
• Waste energy


  The energy that is not used by the device for its desired purpose, or not converted into the desired form
• Equations to calculate efficiency

  • Useful Output Energy / Total Input Energy
  • Useful Power Output/Total Power Output
• Consequence of high thermal conductivity


  The rate of energy transfer through the material is higher than for a material with a lower thermal conductivity
• Double-glazed windows have a lower thermal conductivity than single-glazed windows
• Methods to reduce heat loss in a building

  • Double glazing
  • Loft and wall insulation
  • Thicker walls
• Reducing unwanted energy transfer in a mechanical system

  Reduce friction by lubricating moving parts
• How to increase efficiency of a system

  • Reducing waste output (by lubrication, thermal insulation etc.)
  • Recycling waste output (eg. recycling thermal waste energy as input energy)
• Renewable energy resource


  An energy source which can be replenished as it is being used up
• Non-renewable energy resource


  Fossil fuels (for example coal, oil and gas)
• Advantages of generating power using gas rather than coal

  • Flexible Generation: Gas power stations have short start-up times so can be switched on/off more readily
  • Lower emissions of carbon dioxide
• Disadvantages of using renewable energy resources to generate power

  • Output often determined by external factors (like wind speed), so supply is uncertain
  • Renewable fuels often produce less energy per kg (so are less economical)
• Carbon Dioxide contributes to the greenhouse effect, and causes global warming
• Sulphur Dioxide leads to acid rain, which can damage buildings and crops
• Advantages of fossil fuels as an energy resource

  • Reliable: Not dependent on external factors so can generate power anytime
  • Produce large amounts of energy per kg
  • Still relatively abundant, so cost-effective
• Advantages of nuclear power

  • Very large amounts of energy per kg of fuel
  • No greenhouse gases released, so doesn't contribute to climate change
  • Low fuel costs
• Disadvantages of nuclear power

  • Produces nuclear waste which is harmful to humans & must be safely stored for centuries
  • Non-Renewable energy source
  • Risk of nuclear accidents, which have fatal consequences on humans and the environment
• Social factors to consider in energy production

  • Visual Pollution
  • Sound Pollution
• How hydroelectric power produces energy

  1. Rainwater collects behind a dam

  2. When this water is released, it is used to turn a turbine

  3. This turbine turns a generator which produces electricity
• Disadvantages of using biofuels

  • When plants are burned/decay they release CO2
  • In order to grow biofuels, you need to destroy land: Habitat destruction, CO2 released when plants are cleared (for example, if they are burned)
  • Growing biofuels reduces the land available for food crops
• Advantages of tidal energy sources

  • No greenhouse gases
  • Fairly reliable - tides occur twice a day
  • Cheap to run as tides are natural, so free
• Disadvantages of hydroelectric power

  • The dam may cause flooding
  • It can cost a lot to install the required infrastructure
• Advantages of solar panels

  • They don't cause harm to the environment
  • They are a renewable resource
  • They can be used in remote areas where other types of energy are less accessible