conduction, convection and radiation

• 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 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

  3. Cooler, denser particles sink

  4. Cycle repeats as a convection current
• Reducing convection


  Stop the free flow of fluids, e.g. using a blanket
• Conduction and convection both involve particles gaining kinetic energy
• Conduction only transfers energy between particles, while convection involves the particles themselves moving
• 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 from a hot object without touching it