(energy)

• energy is the ability to do work
• law of conservation of energy is that energy can never be created or destroyed, it is always transffered
• 8 types of energy stores:

  • chemical potential energy (fuel)
  • kinetic energy (moving object)
  • gravitational potential energy (object lifted)
  • thermal energy (heated object)
  • nuclear energy (uranium)
  • elastic potential energy (object is stretched)
  • magnetic potential energy (object in magnetic field)
  • electrical potential energy (object with charge)
• 4 types of energy transfers:

  • mechanical (push, pull, movement)
  • electric (move through voltage)
  • thermal (2 objects with different temperature)
  • waves (light, sound)
• efficiency = (useful output/total output) x 100%
• work done = force x distance (distance must be same direction with force)
• KE = 1/2mv^2
• GPE = mgh
• work done is equal to gravitational potential energy that the object gains
• when an object is dropped from elevation, it transfers from GPE to KE, therefore the two equations can be merged:

  mgh = 1/2mv^2
• power is the rate of which work is done (watt)
• power = work time

  or

  power = force x velocity
• thermal energy is non-mechanical that enters or leaves an object. It is transffered when there is a temperature difference (goes from high to low concentration)
• 4 ways to transfer thermal energy:

  • convection
  • conduction
  • radiation
  • evaporation
• convection is a transfer of thermal energy by the movement of a fluid:

  1. particles increase average KE when heated (move faster)
  2. particles collide harder and more frequently
  3. particles push eachother further apart and hot fluid expands, becomes less dense
  4. hot fluid rises
  5. cooler, denser fluid falls to take place
  6. cycle repeats
• coastal convection current:

  1. sun warms coast
  2. land is warmer than sea
  3. hot air above land rises
  4. cooler air above sea falls
  5. convection takes place

  (day: wind-> land, night: wind-> sea)
• conduction occurs well in solids, poorly in liquids
• conduction:

  1. where the solid is heated, the particles vibrate faster
  2. particles collide with others and make them vibrate more
  3. thermal energy is transffered by 'knock on' vibrations
• thermal radiation is the process which thermal energy is transported by infra-red radiation. infra-red radiation is invisible to the human eye and is part of the electromagnetic spectrum. it can travel without a medium
• shiny silver/white surfaces are the best reflectors of infra-red, black surfaces are the best radiators of infra-red
• a narrower wavelength means greater energy