Topic 1 - Energy

• Energy


  Never created or destroyed, only transferred between different forms and objects
• Forms of energy


  • Thermal or internal energy
  • Kinetic energy
  • Gravitational potential energy
  • Elastic potential energy
  • Chemical energy
  • Magnetic energy
  • Electrostatic energy
  • Nuclear energy
• Energy transfer


  1. Mechanical

  2. Electrical

  3. Heating

  4. Radiation (light or sound waves)
• System


  Collection of matter
• Open system


  Can exchange energy with the outside world
• Closed system


  Separate from the outside world, neither matter nor energy can enter or leave
• Energy transfer example 1


  • Electrical energy from plug socket flows to heating element of kettle, transferred to thermal energy store of heating element, then to water's thermal energy store
• Work done


  Energy transferred
• Types of work done


  • Mechanical
  • Electrical
• Mechanical work done example


  • Kicking a ball up in the air, energy from chemical energy store of leg transferred to kinetic energy store of ball
• Energy transfer example 2


  • Friction between brakes and wheels of train slows it down, transfers energy from kinetic energy store of wheels to thermal energy store of surroundings
• Kinetic energy


  The energy that an object possesses due to its motion
• Kinetic energy


  • Depends on an object's speed
  • Depends on an object's mass
• Faster an object is moving


  More kinetic energy it will have
• More mass an object has


  More kinetic energy it will have
• Calculating kinetic energy


  1. Use equation: E_k = 1/2 m v^2

  2. E_k = kinetic energy

  3. m = mass (in kg)

  4. v = velocity (in m/s)
• Heating an object


  1. Energy is transferred to its thermal energy store

  2. Temperature increases
• Heat transfer

  • Can take place in three different ways depending on the medium involved
  • Conduction in solids
  • Convection in fluids
  • Radiation through empty space
• Conduction


  Vibrating particles transfer energy to neighboring particles
• Heating one end of a metal

  • Energy is transferred to the kinetic energy store of the particles at that end
  • Particles vibrate faster and collide with neighbors more often and with more energy
  • Collisions transfer kinetic energy to neighbors
  • Process repeats until heat is spread out evenly
• Thermal conductivity


  How well objects transfer energy by conduction
• Thermal conductivity


  • Metals have high thermal conductivity and transfer heat rapidly
  • Plastics have low thermal conductivity and are used as insulators
  • Fluids have low thermal conductivity
• Convection


  1. Heated fluid particles gain kinetic energy and move around faster by random diffusion

  2. Warmer, less dense particles rise above cooler, denser particles

  3. Cooler particles sink down and take their place

  4. Cycle repeats as long as fluid is being heated, creating a convection current
• To reduce convection


  Stop the free flow of fluids, like sleeping under a blanket
• Conduction and convection both involve particles gaining kinetic energy, but in conduction only the energy is transferred between particles, while in convection the particles themselves move
• Radiation


  1. Energy is carried by infrared waves

  2. All objects constantly absorb and emit radiation

  3. Hotter objects emit more radiation
• Infrared radiation can be felt when putting a hand over a hot barbecue, even without touching it
• Energy resources


  • Fossil fuels
  • Nuclear fuels
  • Biofuels
  • Wind
  • Hydroelectricity
  • Geothermal
  • Tides
  • Sun
  • Water waves
• Fossil fuels


  • Non-renewable
  • Releases CO2