Conduction/convection

• 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
• Convection current

  The cycle of heated fluid particles rising and cooler particles sinking
• 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 from a hot object can be felt without touching it