physics paper 1 separetes aqa

• Stores of energy


  • Gravitational potential
  • Nuclear
  • Kinetic
  • Thermal
  • Elastic potential
  • Magnetic
  • Chemical
• Units of energy


  Joules, J
• The law of conservation of energy states that: Energy cannot be created or destroyed, only shifted between stores. The total amount of energy is always the same.
• Energy dissipation


  Energy has spread out, usually to the thermal store of the surroundings
• System


  An object or a group of objects
• Open system


  • External forces act
  • Energy is dissipated
• Closed system


  • No external forces act
  • No energy is dissipated
• 1 kJ


  1000 J
• 1 MJ


  1 000 000 J
• A ball is thrown upwards

  • Gravitational store increases
  • Kinetic store decreases
• A piece of coal is burnt

  • Chemical store of coal decreases
  • Thermal store increases
• A car uses its brakes to slow down

  • Kinetic store decreases
  • Thermal store of brakes increases
• An object is dropped and doesn't bounce

  • Kinetic store decreases during impact with floor
  • Thermal store of ball and floor increase
• A car accelerates with a constant force

  • Chemical store of fuel or battery decreases
  • Kinetic store of car increases
• Two magnets with opposite poles are released

  • Magnetic store of the magnets decreases
  • Kinetic store of the magnets increases
• Work


  The amount of energy shifted
• Mechanical work


  The energy shifted by a force
• Units of work


  Joules, J
• Forces that work is done against

  • Gravity
  • Friction
  • Magnetic force between magnets
• Power


  The rate of energy transfer (or the rate of work done). This is the energy transferred (or work done) per second.
• Units of power


  Watts, W
• One watt is the same as 1 Joule per second.
• Efficiency


  The fraction of the total energy that is useful
• Units of efficiency


  Efficiency has no units, because it is a ratio. Efficiencies are written as a decimal or a percentage.
• It is impossible to have an efficiency of 1 for an energy transfer because some energy is dissipated to other non-useful stores
• Reducing energy dissipation for objects moving through air or water


  Make them more streamlined, to reduce the amount of drag/air resistance on the object
• Reducing energy dissipation for surfaces moving against each other

  Lubricate the surfaces with oil, to reduce the amount of friction
• Reducing energy dissipation for a house


  • Loft insulation
  • Cavity wall insulation
  • Double glazing
  • Use materials with low thermal conductivity
• Materials with a high thermal conductivity have a higher rate of cooling
• Metal is an example of a material with a high thermal conductivity
• Gravitational potential energy


  The energy store of an object due its height from the ground
• Kinetic energy


  The energy store of a moving object. (kinetic is from a Greek work "kinesis" meaning motion)
• When an object thrown upwards is at its maximum height, its kinetic energy is empty
• If there is a closed system, with no external forces (air resistance) acting on the object, all the energy in the gravitational store will be shifted to the kinetic store as the object falls to the ground
• A penny dropped from a building has 21 J of gravitational potential energy. Before it hits the floor it has 18 J of kinetic energy. 3 J of energy has been dissipated to the thermal store of the air due to air resistance.
• Non-renewable energy resources


  Energy resources that will run out and cannot be replenished
• Non-renewable energy resources


  • Fossil fuels: oil, coal, gas
  • Nuclear power (uranium, plutonium)
• Renewable energy resources


  Energy resources that will never run out or can be replenished as they are used
• Ways energy resources can be used

  • For heating
  • For transport
  • For electricity generation
• Using fossil fuels


  Burning fossil fuels releases carbon dioxide, which contributes to global warming