Physics

• Stores of energy


  • Chemical
  • Gravitational
  • Potential
  • Kinetic
  • Thermal
  • Elastic Potential
  • Nuclear (radiation)
  • Magnetic
  • Electrostatic
• Energy can not be created or destroyed it can only be converted from one form to another
• Energy changes in a light bulb


  1. Initial source of energy: Electrical

  2. Energy forms after transformation: Heat + Light
• Energy changes in a ball falling in the air

  1. Initial source of energy: Gravitational potential

  2. Energy forms after transformation: Kinetic
• Energy changes in an electric heater being switched on


  1. Initial source of energy: Electrical

  2. Energy forms after transformation: Heat
• Energy changes in an arrow being fired

  1. Initial source of energy: Elastic potential

  2. Energy forms after transformation: Kinetic
• Heat is wasted - it is given to the surroundings. Wasted energy is virtually always given to surroundings as heat.
• Practical stations


  • Wooden block drop
  • Burning candle
  • Radio: switch on and off
  • Wind up toy: wind up and let it move
  • Torch: switch on
  • Dynamo connected to lamp
  • Kettle: boiling water
  • Motor: switch on
• A parachute falls towards earth

  Gravitational potential energy decreases
• Electrical energy is transferred to wind energy

  False
• Electrical energy is transferred to heat


  True
• Other sources electrical energy is transferred to
• Joule


  Unit of energy
• Potential


  Stored energy
• Transfer


  Movement of energy
• Energy cannot be destroyed, it can be lost from a system and appear wasted, but it has just been transferred to the surroundings
• Pendulum swing


  1. Lots of GPE at the top of the swing

  2. Kinetic energy as it descends

  3. GPE again
• Pendulum will not swing forever

  Some energy is lost due to friction/heat loss at the fastening and air resistance
• Clock ticking


  Spring is wound and elastic potential energy store transfers energy to keep the clock ticking
• Work


  When you push or pull something and make it move, you do work on that object
• Key words


  • Work
  • Friction
  • Force
  • Distance
• Work done


  Force (N) x Distance (m)
• Work done on the object

  The amount of energy transferred to the object
• One joule of work is done when a force of one newton causes a displacement of one metre
• Work done/Total energy transferred

  Force (N) x Distance (m)
• Frictional forces occur


  Energy is 'lost' or not used effectively (conservation of energy)
• Work done against friction

  Frictional force x Distance
• All objects with mass produce a gravitational field
• Weight


  The force acting on an object due to gravity, measured in newtons (N)
• Gravitational field strength (g)


  Measured in newtons per kilogram (N/kg), the Earth's is 9.8 N/kg
• Moon has a smaller mass


  The force of gravity is less
• Gravitational potential energy is the amount of energy an object has because of its position above the ground, i.e. its height
• When a bungee jumper falls, he loses GPE. When the cord pulls him back up he gains GPE
• Equation for GPE


  ∆Ep = m g ∆h
• You use energy when you hold an object stationary in your outstretched hand. The energy must be supplied to your muscles to keep them contracted
• Symbols in GPE equation

  ∆Ep = change in gravitational potential energy, m = mass, g = gravitational field strength, ∆h = change in height