Topic 3 ~ Energy

• Equation: ∆𝐺𝑃𝐸 = 𝑚𝑔∆ℎ
• The equation is used to work out the change in GPE as an object is moved from one height to another
• Equation: ∆𝐺𝑃𝐸 = 𝑚𝑔∆ℎ

  Change in gravitational potential energy (joule, J) = mass (kilogram, kg) × gravitational field strength (newton per kilogram, N/kg) × change in vertical height (metre, m)
• Equation: 𝐾𝐸 = 1/2 𝑚𝑣^2
• The equation is used to calculate the amounts of energy associated with a moving object
• Equation: 𝐾𝐸 = 1/2 𝑚𝑣^2


  Kinetic energy (joule, J) = ½ x mass (kilogram, kg) × (speed)2 (metre/second2, m/s2)
• Energy Transfer


  • Diagrams show energy input and the energy output
  • Forms that the energy takes
  • Waste output energy
  • Motors waste energy as heat
• Energy Changes

  • Object projected upwards: KE transferred to GPE, then vice versa as it falls back down
  • Object projected up a slope: KE transferred to GPE (and also to heat if friction is present)
  • Moving object hitting an obstacle: KE transferred to sound / KE transferred to obstacle if that moves too
  • Object being accelerated by a constant force: Object is having work done to it, gaining KE
  • Vehicle slowing down: KE transferred to heat (through brakes)
  • Boiling water in kettle: Electrical energy to thermal
• Conservation of Energy

  • In physics, total energy of an isolated system remains constant
  • Closed system has no external forces acting on it
  • Total energy in a closed system never changes
  • In a closed system, no energy is lost
  • Once it becomes an open system, energy can be transferred out of the system
  • Total energy of the system can change
• Mechanical Waste Energy


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

  • Bulb
  • Electric
  • Light
  • Heat
• 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
• Forms of Waste Energy

  • Light
  • Sound
  • Heat
• To reduce waste energy

  1. Lubricate systems to reduce friction and heat creation

  2. Thermal insulation to reduce heat loss to surroundings

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

  4. Cavity wall insulation to prevent heat loss by convection
• Efficiency


  Ratio of useful output over total input of energy
• Efficiency can be increased by

  1. Reducing waste output via lubrication/thermal insulation or other methods

  2. Recycling waste output and using it as input

  3. Suitable methods depend on each situation
• Energy Sources

  • Fossil Fuels
  • Nuclear Fuel
  • Bio-Fuel
  • Wind
  • Hydro-electricity
  • Tidal
  • Solar
• Non-renewable energy is used more for large-scale energy supplies due to the large energy output per kilogram of fuel. Renewable resources cannot provide such a large amount of energy as easily
• Renewable energy has become more important due to the finite lifetime of fossil fuels, and so their development has become more important
• During the industrial revolution, fossil fuels became an important source of energy as they were easy to mine and provided a lot of energy
• Only recently has renewable energy become more suitable. Technology has had to develop a lot since the industrial revolution to be able to harness such energy sources efficiently