Energy changes in a system

• Kinetic energy equation

  $\dfrac{1}{2} m v^2$
• Kinetic energy equation (words)

  $0.5\times mass \times velocity^2$
• Elastic potential energy equation

  $\dfrac{1}{2} k x^2$
• Gravitational potential energy equation

  $mgh$
• Gravitational potential energy equation (words)

  $mass \times gravity \times height$
• Two equations for power

  $\dfrac{energy\hspace{2mm}transferred}{time} \hspace{5mm} OR \hspace{5mm}\dfrac{work\hspace{2mm}done}{time}$
• Unit of power

  Watt
• Describe energy changes when ball is thrown upwards and returns to starting point

  Upwards: Kinetic energy converted to gravitational potential energy. At peak, maximum GPE, minimum KE. Downwards: Gravitational potential energy converted to Kinetic Energy.
• Describe energy transfers for a bungee jumper

  When falling and cord is loose, gravitational potential energy is converted to kinetic energy of the person. As the cord tightens kinetic energy is converted to elastic potential energy. At lowest point person's initial gravitational potential energy equals elastic potential energy in cord. Cord then recoils and pulls person back up. They don't get back to original height as some energy dissipated to thermal store of surroundings as cord heats up as it stretches.

  
• Chemical energy store example

  Food, fuel, batteries
• Energy stores

  King Charles eats 9 eggs in my garden.

  • kinetic
  • chemical
  • electrostatic
  • nuclear
  • elastic potential
  • internal (thermal)
  • magnetic
  • gravitational potential
• Equation Work Done

  Force x Distance
• Why do surfaces get hot if you rub them together

  work done to overcome friction is transferred as energy to the thermal energy stores of the objects
• Elastic potential energy (words)

  $0.5 \hspace{1mm}\times spring\hspace{1mm}constant\hspace{1mm}\times extension^2$