topic 3 - conservation of energy

• formula for efficiency

  efficiency = useful energy output / total energy output x 100
• what unit is efficiency measured in

  percentage
• facts about efficiency

  -all devices have efficiency but some is always wasted

  -the efficiency can never be equal to or higher than 100%
• the thicker the arrow in a sankey diagram…

  the more energy it represents
• when is energy useful ?

  energy is only useful when transferred usefully. the wasted energy is transferred to less useful sources
• acronym to remember energy names

  kids - kinetic

  hate - heat

  learning - light

  G - gravitational

  C - chemical

  S - sound

  E - elastic

  energy - electrical

  names - nuclear
• kinetic energy stores

  anything that is moving has energy in it’s kinetic energy store. energy is transferred here when an object speeds up but is transferred away when it slows down
• formula for kinetic energy

  kinetic energy = 1/2 x mass x velocity^2

  KE = 1/2 x m x v^2

  ( mass ) ( velocity ( speed ) )
• four main ways energy can be transferred

  -mechanically

  -electrically

  -by heating

  -by light and sound
• mechanically

  when a force makes something move

  example : pulling, stretching or squishing
• electrically

  when electric charges move around and electric circuit due to a potential difference
• by heating

  when energy is transferred from hotter objects to cooler objects

  example : boiling
• by light and sound

  when light or sound waves carry energy from one place to another
• a ball rolling up a slope

  energy is transferred mechanically from the kinetic energy store to the gravitational potential energy store of the ball and the slope ( due to friction ) and then by heating to the thermal energy stores of surroundings ( wasted energy )
• gravitational potential energy

  GPE is the amount of energy an object has because its height
• formula for GPE

  GPE = mass x gravitational field strength x height

  GPE = m x gfs x h
• home insulation

  the roof - loft insulation with fibreglass

  the walls - fit cavity insulation ( polyester boards )

  the floor - fit carpet

  the windows - fit double glazing and curtains

  the doors - gaps have fit draught excluded
• conduction

  transfer of heat energy between two objects in direct contact. when faster moving particles in the hotter object collide with slower moving particles in the cooler objects

  example : a metal spoon heating up when you stir hot soup
• convection

  transfer of heat energy by the movement of fluids. this happens when the hot fluid rises and the cold fluid sinks

  example : a pot of water boiling on the stove
• radiation

  transfer of heat energy by electromagnet waves. when all objects with a temperature above zero emit electromagnet waves. the hotter the object, the more electromagnets it emits

  example : the warmth you feel from the sun
• non renewable energy sources

  -coal

  -oil

  -natural gas

  -nuclear fuels

  these will all run out eventually as they are being used up faster than the rate they are being created + the emissions from burning them harms the environment
• renewable energy sources

  -wind

  -tides

  -hydroelectricity

  -biofuels

  -solar

  these can be made at the rate of usage. some still damage the environment but much less. they don’t produce as much energy as non-renewable sources and some are unreliable as they are weather dependent