Topic 3 - Conservation of energy

• Equation: 𝐾𝐸 = 1/2 𝑚𝑣^2
• Kinetic energy

  Kinetic energy (joule, J) = ½ x mass (kilogram, kg) × (speed)2 (metre/second2, m/s2)
• The equation is used to work out the change in GPE as an object is moved from one height to another
• Mechanical Waste Energy

  In mechanical processes, energy transferred to it can cause a rise in temperature. Energy is dissipated to surroundings, making the process wasteful
• Energy Changes


  1. Object projected upwards: KE transferred to GPE, then vice versa as it falls back down

  2. Object projected up a slope: KE transferred to GPE (and also to heat if friction is present)

  3. Moving object hitting an obstacle: KE transferred to sound / KE transferred to obstacle if that moves too

  4. Object being accelerated by a constant force: Object is having work done to it, with it gaining KE. Whatever supplies the force is having its energy transferred to KE

  5. Vehicle slowing down: KE transferred to heat (through brakes)

  6. Boiling water in kettle: Electrical energy to thermal
• Equation: ∆𝐺𝑃𝐸 = 𝑚𝑔∆ℎ
• Change in gravitational potential energy

  Change in gravitational potential energy (joule, J) = mass (kilogram, kg) × gravitational field strength (newton per kilogram, N/kg) × change in vertical height (metre, m)
• The equation is used to calculate the amounts of energy associated with a moving object
• Energy Transfer

  1. Diagrams show energy input, and the energy output

  2. Forms that the energy takes

  3. Waste output energy

  4. Motors waste energy as heat
• Conservation of Energy

  1. In physics, conservation of energy means that the total energy of an isolated system remains constant

  2. A ‘closed system’ has no external forces acting on it

  3. In a closed system, the total energy in the system never changes, regardless of the energy transfers that take place. In other words, in a closed system no energy is lost

  4. Once it becomes an open system, energy can be transferred out of the system, and therefore the total energy of the system can change
• Forms of energy

  • Bulb
  • Electric
  • Light
  • Heat
• To reduce waste energy

  1. Lubricate systems to reduce friction and heat creation

  2. Thermal insulation to reduce heat loss to surroundings
• Efficiency


  Ratio of useful output over total input of energy
• Mechanical Waste Energy


  1. Energy transferred to objects can cause a rise in temperature

  2. Energy is dissipated to surroundings, heat is transferred to air, making the process wasteful
• Energy Sources

  • Fossil Fuels
  • Nuclear Fuel
  • Bio-Fuel
  • Wind
  • Hydro-electricity
  • Tidal
  • Solar
• Only recently has renewable energy become more suitable, and technology has had to develop a lot since the industrial revolution to be able to harness such energy sources efficiently
• Renewable energy has become more important due to the finite lifetime of fossil fuels, and their development has become more important
• The total energy of the system can change

  Mechanical Waste Energy
• Forms of Waste Energy

  • Light
  • Sound
  • Heat
• Buildings

  1. Thicker walls for greater thermal insulation and less heat loss

  2. Cavity wall insulation fills air cavities between walls to prevent heat loss by convection
• Non-renewable energy is used more for large-scale energy supplies due to the large energy output per kilogram of fuel, while renewable resources cannot provide such a large amount of energy as easily
• Efficiency


  Can be increased by reducing waste output, recycling waste output, and using it as input
• During the industrial revolution, fossil fuels became an important source of energy as they were easy to mine and provided a lot of energy