P1 - Energy stores and transfers

• System


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


  • A system where no energy ccan escape or enter from the surroundings
  • The total energy in a closed system never changes
• Kinetic energy store


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


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


  Energy an elastic object has when it is stretched or compressed
• Thermal/internal energy store


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


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


  Energy stored in the nucleus of an atom
• Magnetic energy store


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


  Energy a charged object has when near another charged object
• Energy transfer by heating


  Energy is transferred from one object to another object with a lower temperature
• Energy transfer by waves


  Waves (e.g. light and sound) can transfer energy by radiation
• Energy transfer through electricity


  When an electric current flows it can transfer electricity
• Energy transfer through forces (mechanical work)

  Energy is transferred when a force moves or changes the shape of an object
• gravitational field energy (J) = mass (kg) x gravitational field strength (N/kg) x height (m)
• kinetic energy (J) = 0.5 x 1/2 x mass (kg) x speed^2 (m/s)
• power (W) = energy transferred (J)/time (s)
• power (W) = work done (J)/time (s)
• elastic potential energy (J) = 0.5 x spring constant (N/m) x extension^2 (m)
• Power


  How much energy is transferred or work is done per second
• Energy cannot be created or destroyed - it can only be transferred usefully, stored, or dissipated to the surroundings
• Dissipated energy is often described as being wasted
• Energy is never entirely transferred usefully - some energy is always wasted (transferred to less useful stores)
• 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
• Using thermal insulation is a way of reducing energy wasted due to heat dissipated to the surroundings
• Efficiency


  A measure of of how much energy is transferred usefully
• efficiency = useful energy out (J)/total energy in (J)
• efficiency = useful power out (W)/total power in (W)