Physics p1

• System

  An object or group of objects
• Whenever anything changes in a system, energy is transferred between its stores or to the surroundings
• Energy stores

  • kinetic
  • gravitational potential
  • elastic potential
  • thermal (or internal)
  • chemical
  • nuclear
  • magnetic
  • electrostatic
• Kinetic energy

  Energy an object has because it is moving
• Gravitational potential energy

  Energy an object has because of its height above the ground
• Elastic potential energy

  Energy an elastic object has when it is stretched or compressed
• Thermal (or internal) energy

  Energy an object has because of its temperature (the total kinetic and potential energy of the particles in the object)
• Chemical energy

  Energy that can be transferred by chemical reactions involving foods, fuels, and the chemicals in batteries
• Nuclear energy

  Energy stored in the nucleus of an atom
• Magnetic energy

  Energy a magnetic object has when it is near a magnet or in a magnetic field
• Electrostatic energy

  Energy a charged object has when it is near another charged object
• Closed system

  One where no energy can enter from the surroundings. The total energy in a system never changes.
• Energy transfers

  • Heating
  • Waves
  • Electricity
  • Forces (mechanical work)
• Heating

  Energy is transferred from one object to another object with a lower temperature
• Waves

  Waves (e.g., light and sound waves) transfer energy
• Electricity

  When an electric current flows it transfers energy
• Forces (mechanical work)

  Energy is transferred when a force moves or changes the shape of an object
• Heating bills can be expensive so it is important to reduce the rate of heat loss from buildings
• Factors that affect the rate of heat loss from a building

  • Thickness of its walls and roof
  • Thermal conductivity of its walls and roof
• Thermal conductivity

  The rate of energy transfer through a material
• Thermal insulator

  A material that has a low thermal conductivity. The rate of energy transfer through an insulator is low.
• Factors that determine the energy transfer per second through a material

  • The material's thermal conductivity
  • The temperature difference between the two sides of the material
  • The thickness of the material
• Thermal insulation materials

  • Loft insulation
  • Cavity wall insulation
  • Aluminium panel and double glazing
  • Draught excluder
• Gravitational potential energy

  Depends on an object's height above the ground, the gravitational field strength, and its mass
• Kinetic energy

  Depends on an object's mass and speed
• Power

  How much work is done (or how much energy is transferred) per second
• Elastic potential energy

  The energy stored in a stretched spring
• Energy cannot be created or destroyed - it can only be transferred usefully, stored, or dissipated (wasted)
• Dissipated energy is often described as being wasted
• All energy eventually ends up transferred to the thermal energy store of the surroundings
• In machines, work done against the force of friction usually causes energy to be wasted because energy is transferred to the thermal store of the machine and its surroundings
• Lubrication

  A way of reducing unwanted energy transfer due to friction
• Streamlining

  A way of reducing energy wasted due to air resistance or drag in water
• Thermal insulation

  A way of reducing energy wasted due to heat dissipated to the surroundings
• Most of our energy currently comes from fossil fuels - coal, oil, and natural gas
• Non-renewable energy resources

  Not replaced as quickly as they are used, will eventually run out
• Reliable energy resources

  Available all the time (or at predictable times) and in sufficient quantities
• Both renewable and non-renewable energy resources have some kind of environmental impact when we use them
• Renewable energy resources

  Can be replaced at the same rate as they are used, will not run out
• Renewable energy resources

  • Solar
  • Tidal
  • Wave
  • Wind
  • Geothermal
  • Biofuel
  • Hydroelectric