Effects Of  Heat  Energy
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  • 1. Effects of Heat Energy Pages 118 to 125
  • 2. Think, pair, share
    • Why you think that there are gaps in between the railway track?
  • 3. Objectives 1
    • State the forces of expansion and contraction in solids
    • State examples and applications of heat energy in solids
  • 4. Heat Energy
    • Objects heated – Size increase, EXPANSION
    • Objects cooled – Size decrease, CONTRACTION
    • Expansion and contraction occurs in all 3 states of matter – solid, liquid and gas
  • 5. Effect of heat energy - Solid
    • Expansion and contraction of solids are so small
    • Different metals expand and contract at different times and by different amounts
    • Examples
      • Railway tracks will expand on hot days if no gap very dangerous, train can derail and endanger passengers
      • Bridges have fitted rollers to allow for expansion and contraction, allow bridge to slide over them smoothly when expanded
      • Overhead cables and telephone lines expand during hot and contract and become taut on cold days. Hang loosely.
  • 6. Effect of heat energy - Solid
    • Examples
      • Concrete surfaces such as road and paths expand when heated, small gaps found every few meters in the concrete roads and paths
      • Pipes carrying water or steam are looped at intervals to allow for expansion. If not the pipes will burst
  • 7. Applications of heat energy - Solid
    • Rivets are used to join two steel plates together. Hot rivet is driven through the hole in the plates. One end of the rivet is hammered to form a new rivet head. When cool, the rivet will contract and held the two plates tightly together
    • http://www.bbc.co.uk/schools/ks3bitesize/science/chemistry/particle_model_5.shtml
  • 8. Applications of heat energy - Solid
    • Bimetallic strips made up of two different metal, steel/iron and brass
    • Hotter bend downwards, colder bend upwards
    • Both metals expand and contract by different amounts.
    • Brass expands and contracts more than steel
  • 9. Applications of heat energy - Solid
    • Bimetallic strips is use in thermostats in refrigerators, ovens, irons and heaters
    • Regulate the temperature of these appliances
    • It is also used in fire alarms, when the strip gets hot, it bends and completes an electrical circuit. A bell in the circuit rings to warn of a fire
  • 10. Review Questions
    • Do Checkpoint Question 1 pg 120
    • Do Inquiry time Question 1 pg 121
    • Do Checkpoint Question 2 pg 122
  • 11. Objectives 2
    • State the forces of expansion and contraction in liquids
    • State examples and applications of heat energy in liquids
  • 12. Effect of heat energy - Liquid
    • Almost all liquids expand when heated and contract when cooled
    • Drink factories need to allow space when filling up their bottles or cans
    • No allowance will caused the bottles or cans to burst
  • 13. Application of heat energy - Liquid
    • Liquid in glass thermometer
    • Mercury or alcohol thermometers
    • Thermometer is filled with mercury or alcohol in the bulb
    • When in contact with cold substances mercury/alcohol will contract and the mercury/alcohol thread will drop
    • When in contact with hot substances mercury/alcohol will expand and causing the mercury/alcohol thread to rise
  • 14. Unique quality of water
    • Water expand when it is being cooled from 4 ˚ C to 0 ˚ C
    • Starts to contract when heated from 0 ˚ C to 4 ˚ C
    • It reaches its minimum volume and maximum density at 4 ˚ C
  • 15. Objectives 3
    • State the forces of expansion and contraction in gases
    • State examples and applications of heat energy in gases
  • 16. Effect of heat energy - Gases
    • Gases expand when heated and contract when cooled
    • Gases expand and contract much more than solids and liquids of the same volume for the same change in temperature
  • 17. Effect of heat energy - Gases
    • Example, we should not pump car tyres to the maximum pressure on hot days – may burst
  • 18. Application of heat energy - Gases
    • Hot balloon uses the expansion of gases
    • Filled with heated air
    • As volume of air increases (expansion), the density of air decreases
    • Warm air less dense this it rises and carries the balloon upwards
  • 19. Application of heat energy - Gases
    • Baking bread or cake, baking powder is added
    • Carbon dioxide gas is released from the baking powder expands
    • Causing the dough to rise
  • 20. Review Questions
    • Do Checkpoint Question 2 pg 120
    • Do Checkpoint Question 3 pg 122
  • 21. Objectives 4
    • Explain using a particulate model for expansion and contraction
  • 22. Expansion and Contraction
    • When substances expand or contract, the particles stay the same size
    • Only the spaces between the particles changes
    • The particles in the solid vibrate more when it is heated thus take up more room - EXPANSION
    • Similar to liquid and gases when heated
  • 23. Expansion and Contraction
    • The particles in solid will vibrate less when it is cold thus take up less space – CONTRACTION
    • Similar to liquid and gases when cooled
  • 24. Review Questions (page 125)
    • Do it now!