P1.1

• Law of Conservation of Energy

  Never created or destroyed, only transferred between different forms and objects
• Energy Store

  • Thermal energy
  • Kinetic energy
  • Gravitational potential energy
  • Elastic potential energy
  • Chemical energy
  • Magnetic energy
  • Electrostatic energy
  • Nuclear energy
• Energy transfer


  1. Mechanical

  2. Electrical

  3. Heating

  4. Radiation (light or sound waves)
• System


  Collection of matter
• Open system


  Can exchange energy with the outside world
• Closed system


  Separate from the outside world, no exchange of matter or energy. The overall charge is always zero.
• Explain how energy is transferred when a kettle boils water

  • Electrical energy from plug socket flows to heating element of kettle, transferred to thermal energy of water
• Work done


  Energy transferred
• Mechanical work done example

  • Kicking a ball, energy from chemical energy store of leg transferred to kinetic energy of ball
• Electrical work done example

  • Energy required to overcome resistance in wires of a circuit
• Energy transfer example 2

  • Friction from train brakes slows the train, transfers energy from kinetic energy store of wheels to thermal energy of surroundings
• Energy Stores

  • Thermal
  • Kinetic
  • Gravitational potential
  • Elastic potential
  • Chemical
  • Magnetic
  • Electrostatic
  • Nuclear
• When energy is transferred to an object...


  The energy is stored in one of the object's energy stores
• System


  A single object or a group of objects that you're interested in
• Closed system


  • A system where neither matter nor energy can enter or leave
  • The net change in the total energy of a closed system is always zero
• Energy transfer by heating

  Energy is transferred to the water's thermal energy store (causing the temperature of the water to rise)
• Energy transfer by doing work (work done)

  1. Work done is just another way of saying energy transferred

  2. Work can be done when current flows or by a force moving an object
• Energy transfers


  • Initial force exerted by a person to throw a ball upwards transfers energy from the chemical energy store of the person's arm to the kinetic energy store of the ball and arm
  • Gravitational force on a dropped ball transfers energy from the ball's gravitational potential energy store to its kinetic energy store
  • Friction between a car's brakes and its wheels transfers energy from the wheels' kinetic energy stores to the thermal energy store of the surroundings
  • Normal contact force in a car collision transfers energy from the car's kinetic energy store to other energy stores, e.g. the elastic potential and thermal energy stores of the object and the car body
• Energy is transferred by heating, by waves, by an electrical current, or a force when it moves some object
• Energy is measured in joules (J)
• Where object falls and gains speed, its store of gravitational potential energy decreases and its kinetic energy store increases
• When a object hits the ground without bouncing back, its kinetic store decreases. Some or all of its energy transferred to the surroundings – the thermal energy store of the surroundings increases and energy is also transferred by sound wave.
• State the law of conservation on energy

  Energy is never created or destroyed. It's only ever transferred between different forms and objects (stores of energy).
• State the different ways in which energy can be transferred between stores.

  • Mechanically
  • Electrically
  • Heating
  • Radiation
• Examples of chemical energy stores

  • Food
  • Fuel
  • Batteries