Section 4 : Energy Resources and Energy Transfer

• System

  • An object or a group of objects
  • When a system changes, there are changes in the way energy is stored
• Closed system


  Neither matter nor energy can enter or leave the system
• Energy stores

  • Gravitational
  • Elastic
  • Thermal
  • Magnetic
  • Electrostatic
  • Nuclear
  • Chemical
  • Kinetic
• Energy changes when throwing a ball upwards

  1. Begin throwing - kinetic energy store

  2. Ball at highest point - gravitational potential energy store

  3. Just before catching ball - kinetic energy store
• Energy pathways

  
  

  Mechanically

  Electrically

  heating

  radiation
• Energy pathway in a ball dropped

  1. Energy store before drop: gravitational

  2. Energy store increased as it falls: kinetic

  3. Energy transfer between stores: mechanical or elastic if the ball is bouncy
• Energy pathway in a car accelerating from stop

  1. Energy store at start: chemical

  2. Energy transfer/pathway: mechanical (force)

  3. Energy store at end: kinetic
• The law of conservation of energy states that energy can not be created or destroyed, it is passed on from one form to another
• 1. Friction between moving parts causes heating - reduce with lubrication

  2. Heat loss - reduce with insulation
• Sankey Diagram = A diagram that shows the flow of energy through a system.
• Efficiency = useful energy/total energy
• Energy is only useful when it is transferred from one store to a useful store
• Total energy input = useful energy + waste energy

  Less energy wasted = More efficient
• Conduction - energy transfer by heating in solids
• Convection - energy transfer by heating in liquids and gases
• Cat X has no fur and light skinned

  Cat Y has thick, black fur

  Comparison:

  • Cat X loses more heat than Cat Y because Cat Y has thick fur to trap air -> air & fur good insulators so Cat Y loses less heat by conduction -> trapped air cannot move, reduces heat loss by convection
  • Cat Y loses more heat by radiation than Cat X because black surfaces emit radiation faster
• Formation of Convection Current:

  • Particles near a heat source become hotter and rise up -> lose density + expands
  • Hot particles move away and become colder -> contract + become more dense
  • Colder particles sink to the bottom
  • Convection current process repeats until a fluid reaches room temp.
• Kinetic energy (Ke) = 1/2 mv^2
• Power = work done (J)/Time
• GPE = m x g x h