Energy

• SI units for kinetic energy equation

  • Energy (J), Mass(kg), Velocity(m/s)
• SI units for elastic potential energy equation

  • Energy (J), Spring Constant (N/m), Extension(m)
• SI units for gravity potential energy equation

  • Energy (J), Mass(kg), Gravitational Field Strength (N/kg), Height (m)
• Specific Heat Capacity


  The amount of energy needed to raise the temperature of 1 kilogram of a substance by 1 degree Celsius
• Units for Specific Heat Capacity

  • J/°C/kg
  • Joules/Degree Celsius/Kilogram
• Power


  The rate at which energy is transferred (or rate at which work is done)
• Equations for power


  • power = energy transferred/time
  • power = work done/time
• SI units for power equations

  • Energy (J), Work Done (J), Time (s)
• Unit of power


  Watt (W)
• Energy changes when a ball is thrown upwards and then returns to its starting position


  1. Upwards: KE is converted to GPE

  2. Peak: Maximum GPE, zero KE

  3. Downwards: GPE is converted to KE
• 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
• Chemical energy stores


  • Food
  • Fuel (eg. wood, coal, petrol)
  • Batteries
• Different stores of energy

  • Kinetic Energy
  • Gravitational Potential Energy
  • Elastic Potential Energy
  • Chemical Energy
• Law of energy conservation


  Energy cannot be created or destroyed (it can only be transferred into different forms)
• The total energy of the system remains constant due to the conservation of energy
• Waste energy


  The energy that is not used by the device for its desired purpose
• 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
• Equations to calculate efficiency

  • Useful Output Energy Transfer/Total Input Energy Transfer
  • Useful Power Output/Total Power Output
• How to increase the efficiency of a system

  1. Reducing waste output (by lubrication, thermal insulation etc.)

  2. Recycling waste output (eg. recycling thermal waste energy as input energy)
• 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
• Factors affecting the rate of cooling of a building

  • The thickness of the walls
  • The thermal conductivity of the walls
• Methods of reducing heat loss in a building

  • Double glazing
  • Loft and wall insulation
  • Thicker walls
• How to improve the efficiency of a mechanical machine with moving parts

  Lubricate any moving parts to reduce the friction and therefore energy loss due to heating
• How to improve the efficiency of a radiator

  Installing metal foil sheets behind the radiator to reflect the heat back into the room rather than it being absorbed into the walls
• How to improve the efficiency of boiling water in a pan

  By placing a lid on the pan to reduce the heat loss from the top
• 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
  • Generating power through other means is often more efficient and economically beneficial
• Burning fossil fuels

  • Carbon Dioxide contributes to the greenhouse effect, and causes climate change
  • 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
  • Can produce large amounts of energy for a given quantity
  • Still relatively abundant, so cost-effective
• Advantages of nuclear power

  • Very large amounts of energy for relatively small quantities of fuel
  • Doesn't release greenhouse gases and 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
• 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 or decay they release CO2
  • In order to grow biofuels, you need to destroy land which leads to problems because: The land could have been natural habitats, Destroying land may involve burning plants growing on it, which would release CO2
  • Growing biofuels reduces the land available for growing food
• Advantages of tidal energy sources

  • They do not produce greenhouse gases
  • They are quite reliable, as tides happen twice a day
  • They are cheap to run as tides are natural, and so are 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