Energy Transfers

• Equilibrium


  When nothing changes and so nothing happens
• Isolated system


  Does not allow the transfer of matter or energy to or from its surroundings
• Closed system


  Can exchange energy but not matter to or from its surroundings
• Open system


  Allows the exchange of energy and matter to or from its surroundings
• Mechanical working


  When a force acts on an object (e.g. pulling, pushing, stretching, squashing)
• Electrical working


  A charge moving through a potential difference (e.g. current)
• Heating (by particles)


  Energy is transferred from a hotter object to a colder one (e.g. conduction)
• Heating by radiation


  Energy transferred by electromagnetic waves (e.g. visible light)
• An Object Projected Upwards

  1. Before the ball is thrown upwards, the person holding the ball has energy in their chemical store

  2. When the ball is thrown, some of that energy is transferred to the kinetic store of the ball as it begins to move upwards

  3. As the height of the ball increases, energy from the kinetic store of the ball is transferred to its gravitational potential store
• A Vehicle Being Accelerated by a Constant Force


  1. When a vehicle is stationary, it has energy in the chemical store of the fuel

  2. When the vehicle speeds up or accelerates, the energy is transferred to the kinetic store of the car
• Boiling Water in a Kettle

  1. When an electric kettle boils water, energy is transferred by electrical working from the mains to the thermal store of the heating element inside the kettle

  2. As the heating element gets hotter, energy is transferred by heating to the thermal store of the water
• Heating


  Energy transfers by heating increase the energy in the kinetic store of the particles that make up that system, which increases the energy in the thermal store of the object
• Energy transfer when warming a pan on a hob

  1. Energy is transferred electrically from the mains supply to the thermal store of the hob

  2. Energy is transferred by heating from the thermal store of the hob to the thermal store of the pan
• Mechanical work


  Mechanical work is done when a force acts over a distance
• Energy transfers when a box is pushed across the floor


  1. If the system is defined as the man and the box, energy is transferred mechanically from the kinetic store of the person to the kinetic store of the box

  2. If the system is defined as the box and the floor, energy is transferred by heating from the kinetic store of the box to the thermal store of the floor (due to friction) and by heating to the thermal store of the surroundings as the sound waves transfer energy away from the system and cause the air particles to vibrate
• Electrical work


  Energy is transferred electrically from the power supply to the components in the circuit
• Energy transfers in an electrical circuit

  1. Energy from the chemical store of the cell is transferred electrically to the thermal store of the lamp as the filament heats up

  2. Energy is transferred from the thermal store of the lamp by heating and by radiation (light) to the thermal store of the surroundings

  3. Energy is also transferred by heating to the thermal store of the wires (due to resistance)