ENERGY

• what is a system?

  an object or a group of objects
• what is a closed system?

  a system where neither matter nor energy can enter or leave
• what are the energy stores?

  kinetic, elastic potential, gravitational potential, magnetic, internal, chemical, electrostatic
• what are the types of energy transfers?

  heating, electrical work, radiation, mechanical work
• what is work done?


  energy transferred
• describe the energy stores when a ball is thrown up in the air

  chemical > kinetic
• describe the energy stores when a ball is being dropped from a height

  gravitational potential > kinetic
• describe the energy stores of an object accelerated by constant forces


  chemical > kinetic
• describe the energy stores of boiling water

  chemical > internal (electrically)
• describe the energy stores of a moving object hitting and obstacle

  kinetic > elastic potential, thermal, sound
• what is kinetic energy?


  energy of movement
• what is the equation for kinetic energy?


  ke = 1/2 m v2
• what does kinetic energy depend on?


  mass and speed
• what is elastic potential energy?

  energy stored in an elastic object
• what is the equation for elastic potential energy?


  ee = 1/2 k e2
• what is gravitational potential energy?

  potential energy that depends on height
• what is the equation for gravitational potential energy?


  ep = m g h
• describe the transfer of energy from gravitational potential energy to kinetic energy


  energy lost in g.p.e store = energy gained in kinetic store
• what is the conservation of energy?


  energy cannot be created or destroyed
• how do machines waste energy?

  by transferring energy to the heat store
• what is power?


  the rate of energy transfer
• what is power measured in?


  watts
• what is the equation for power?

  power = energy transferred / time
• what is a powerful machine?


  one which transfers a lot of energy but over less time
• what is efficiency?

  the proportion of input energy that is transferred to a useful form
• how can efficiency be improved?

  insulation, lubrication, streamlining
• what is the equation for efficiency?


  efficiency = useful output / total input
• what is conduction?

  the process where vibrating particles transfer energy to neighboring particles
• where does conduction occur?


  mainly in solids
• what is thermal conductivity?


  a measure of how quickly energy is transferred through a materials via conduction
• what is convection?

  where energetic particles move away from hotter to cooler regions
• why does hot air rise?


  because it is less dense than cold
• what happens if there is a constant heat source in a room?


  a convection current can be created
• what can create convection currents?


  radiators
• what are the best conductors?

  silver, copper, gold, aluminum, zinc
• what are the best insulators?


  glass, air, plastic, rubber, wood
• what is specific heat capacity?

  the amount of energy needed to raise the temperature of 1kg of a substance by 1C
• what is the equation for specific heat capacity?

  change in thermal energy = mass x specific heat capacity x temperature change
• what can reduce frictional forces?


  lubrication
• what does insulation do?

  reduces the rate of energy transfer by heating things that prevent energy losses