Energy

• Kinetic energy equation

  ½ m v2
• Kinetic energy equation

  • Energy (J), Mass(kg), Velocity(m/s)
• Elastic potential energy equation

  ½ k x2
• Elastic potential energy equation


  • Energy (J), Spring Constant (N/m), Extension(m)
• 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
• Specific Heat Capacity


  • J/°C/kg
• Power


  The rate at which energy is transferred (or rate at which work is done)
• Power equations

  • power = energy transferred/time
  • power = work done/time
• Power unit


  • Watt (W)
• Two motors lift the same mass through the same height. Motor A does this in half the time of Motor B.

  Motor A dissipates the most power
• 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
• 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
• Efficiency equation 1

  Useful Output Energy Transfer/Total Input Energy Transfer
• Efficiency equation 2

  Useful Power Output/Total Power Output
• Increasing 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)
• High thermal conductivity of a material

  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 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
• Improving efficiency of a mechanical machine with moving parts

  Lubricate any moving parts to reduce the friction and therefore energy loss due to heating
• Improving 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
• Improving efficiency of boiling water in a pan


  By placing a lid on the pan to reduce the heat loss from the top