Energy changes in a system

• 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