♡ Topic 3_Conservation of energy ♡

• Equation for gravitational potential energy: mgh (Mass x Gravitational Field Strength x Height)

  • SI units: Energy (J), Mass (kg), Gravitational Field Strength (N/kg), Height (m)
• Equation for kinetic energy: ½ m v² (½ x Mass x (Velocity)²)

  • SI units: 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:

  • Upwards: Kinetic Energy (KE) is converted to Gravitational Potential Energy (GPE)
  • Peak: Maximum GPE, zero KE
  • Downwards: GPE is converted to KE
• Total energy of a ball that is kicked:

  • The total energy of the system remains constant due to the conservation of energy
• Energy changes in a filament light-bulb:

  • Electrical energy is transferred into light and heat energy
  • Light is a useful energy form, heat is waste energy
• Energy transfers for a bungee jumper:

  • Falling: GPE is converted to KE of jumper
  • Cord tightens: KE is converted and stored as Elastic Potential Energy (EPE)
  • Lowest point: Jumper’s initial GPE equals the EPE stored in the cord
• Reason why a bungee jumper slows down when the cord stretches:

  • Kinetic energy decreases as it is converted to elastic potential energy
  • Velocity decreases as kinetic energy decreases
• Waste energy:

  • 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 in energy transfer:

  • Rate of energy transfer through the material is higher
• Double-glazed windows vs. single-glazed windows thermal conductivity:

  • Double-glazed windows have lower thermal conductivity
• Methods to reduce heat loss in a building:

  1. Double glazing

  2. Loft and wall insulation

  3. Thicker walls
• Reducing unwanted energy transfer in a mechanical system:

  • Reduce friction by lubricating moving parts
• Increasing efficiency of a system:

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

  2. Recycling waste output (e.g., recycling thermal waste energy as input energy)
• A renewable energy resource is an energy source which can be replenished as it is being used up
• Examples of renewable energy resources:

  • Wind Energy
  • Hydro-Electricity
  • Tidal Energy
  • Solar Energy
• A non-renewable energy resource example: Fossil fuels (e.g., coal, oil, and gas)
• Advantages of generating power using gas instead of 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)
• Environmental impacts of burning fossil fuels:

  • 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:

  1. Reliable: Not dependent on external factors so can generate power anytime

  2. Produce large amounts of energy per kg

  3. Still relatively abundant, so cost-effective
• Advantages of nuclear power:

  1. Very large amounts of energy per kg of fuel

  2. No greenhouse gases released, so doesn’t contribute to climate change

  3. Low fuel costs
• Disadvantages of nuclear power:

  1. Produces nuclear waste which is harmful to humans & must be safely stored for centuries

  2. Non-Renewable energy source

  3. Risk of nuclear accidents, which have fatal consequences on humans and the environment
• Social factors to consider in energy production:

  • Visual Pollution
  • Sound Pollution (both of these are disadvantages of wind farms)
• How hydroelectric power produces energy:

  • Rainwater collects behind a dam
  • When this water is released, it is used to turn a turbine
  • 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 (e.g., 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