Conservation of Energy & Power

• conservation of energy

  energy is neither created or destroyed but transferred, stored or dissipated
• dissipated energy is known as wasted energy as it is stored for something not useful
• power is the rate of energy transfer or the rate of doing work
• equations for power

  p = E/t

  p = W/t
• conduction

  the process where vibrating particles transfer energy to neighbouring particles
• conduction is when energy is transferred to an object by heating is transferred to the thermal store and the energy is shared across the kinetic energy stores of particles in the object . This makes them collide and vibrate more with each other and the process continues till the energy is transferred to the other side of the object .
• thermal conductivity is a measure of how quickly is transferred through a material
• convection

  where energetic particles move away from hotter to cooler regions
• convection is when energy is transferred by heating to the thermal store of a liquid or gas which is shared across the kinetic energy of a liquid or gas causing them to move faster and the space between particles increases.
• convection current in a radiator

  • energy is transferred from the radiator to the nearby air particles by conduction
  • air by the radiator becomes warmer and less dense
  • warm air rises and replaced by cooler air which is then heated by the radiator
  • at the same time the previously heated air transfers energy to surroundings where is cools, becomes denser and sinks
  • cycle repeats causing a flow of air to circulate around the room
• reducing unwanted energy transfers can be done by lubrication or insulation
• lubrication reduces frictional force
• lubricants are usually liquids so that they flow easily between objects and reduce friction when objects they are moving
• insulation reduces the rate of energy transfer of heating
• to prevent energy loss through heating in a house we can have thick walls made from materials with low thermal conductivity