8.1

• 8.1 Describe the changes involved in the way energy is stored when

  systems change

  There are changes in the way energy is stored when a system changes. For example: an object projected upwards - The object's energy is slowly transferred from the kinetic store to the gravitational potential store as it slows down and climbs higher.
• 8.2 Draw and interpret diagrams to represent energy transfers

  .Transfer diagrams

  In transfer diagrams the boxes show the energy stores and the arrows show the energy transfers

  
  

  .Sankey diagrams

  Sankey diagrams start off as one arrow that splits into two or more points. This shows how all of the energy in a system is transferred into different stores.
• 8.3 In a closed system what happens to the total energy of that system when there are energy transfers?


  where there are energy transfers in a closed

  system there is no net change to the total energy in that system
• 8.4 Identify the different ways that the energy of a system can be

  changed

  a) through work done by forces

  b) in electrical equipment

  c) in heating
• Energy is transferred by one of the following four types of energy pathway:

  .mechanical work - a force moving an object through a distance

  .electrical work - charges moving due to a potential difference

  .heating - due to temperature difference caused electrically or by chemical reaction

  .radiation - energy transferred as a wave eg light, infrared, sound - the Sun emits light radiation and infrared radiation
• Describe how heating can change the energy of a system

  Heating changes the energy stored within a system by increasing the energy of the particles that make up that system

  This either raises the system's temperature or, produces a change of state (eg. solid to liquid)

  An example of the energy change by heating is electrical energy to thermal energy
• Describe how work done by forces can change the energy of a system

  When Work is Done against frictional forces, energy is transferred, increasing the temperature of the moving object and the contact surface. When a force is used to move an object, energy is transferred (because the object has moved) and we say that Work is Done

  An example of the energy change by work done by forces is kinetic energy to thermal energy
• Describe an example of how work done in electrical equipment can change the energy of a system

  An example of the energy change by work done when a current flow is chemical energy to electrical energy to thermal energy

  (Chemical energy from the battery is converted to electrical energy in the components and then transferred to heat in wires)
• 8.5 Describe how to measure the work done by a force

  .Find the direction of the force vector and the direction of motion

  .Find the displacement of your object

  .Find the force on the object

  .Multiply Force × Distance

  .Label your answer in joules

  
  

  .work done(J) = force(N) x distance moved in the direction of the force (m)
• 8.5 Energy transferred (joule, J) is equal to...


  work

  done (joule, J)
• 8.7 Describe and calculate the changes in energy involved when a

  system is changed by work done by forces (give an example)

  Bringing water to a boil in an electric kettle

  Electricity through the element of the kettle increases its internal (thermal) energy which increases the internal (thermal) energy of the water which increases the temperature of the water

  (to calculate this select the right equation from the equation sheet)
• 8.10 Explain, using examples, how in all system changes energy is

  dissipated so that it is stored in less useful ways

  No system is perfect. Whenever there is a change in a system, energy is transferred and some of that energy is dissipated.

  Dissipation is a term that is often used to describe ways in which energy is wasted. Any energy that is not transferred to useful energy stores is said to be wasted because it is transferred to the surroundings.

  For example - for a radio or set of speakers the electrical work is transferred into useful sound waves and thermal energy is dissipated causing a rise in the internal energy store (temperature) of the surroundings
• 8.11 Mechanical processes become wasteful when...

  cause a rise in temperature so dissipating energy in heating them surroundings
• 8.12 Define power (and have an exmaple)

  The rate at which energy is transferred

  (An example that illustrates the definition of power is by comparing two electric motors if:

  They lift the same weight

  They are lifted by the same height

  One lifts it faster than the other

  The motor that lifts the weight faster is said to have more power

  This is because the work done does not depend on time, only the force (weight) and the distance lifted)
• 8.14 Recall that one watt is equal to...

  one joule per second ( J/s)