The document discusses different methods of heat transfer including conduction, convection, and radiation. It provides examples of good conductors and insulators of heat, how convection currents transfer heat in liquids and gases, and how all objects can absorb and radiate heat but some surfaces do it faster than others. Real-world applications of heat transfer principles in areas like cooking, heating/cooling buildings, and spacesuit design are also examined.

1. Transmission of Heat Energy CHAPTER FIFTEEN

3. The Movement of Heat Definition: Heat is a form of energy that can move from the hotter object to the cooler one. The temperature of the cooler object rises while that of the hotter one falls until both are at the same temperature. What is Heat ???

5. 15.1 Conduction Definition: Conduction is the movement of heat through a material without the obvious movement of the material itself. What is Conduction ???

6. Good conductors are materials (eg. metals) that allow heat to flow through easily. Insulators (or poor conductors) are materials (eg. plastics) that do not allow heat to flow through them easily. metal spoon very hot water plastic spoon

7. Some metals conduct heat better than others. Silver, gold and copper are the three best conductors of heat. Comparing Conductors and Insulators copper rod iron rod Bunsen burner wax melts first wax melts slower tripod stand

8. Non-metals such as wood, plastics and glass are poor conductors of heat. Liquids and gases are good insulators of heat. Vacuum is the best insulator because an empty space cannot conduct heat. Comparing Conductors and Insulators matchstick does not burn matchstick burns metal rod Bunsen burner

9. Uses of Conductors and Insulators Conductors and Insulators of Heat cooking pan penguin electric iron oven gloves rabbit wool blanket icebox

10. 15.2 Convection Definition: Convection is the movement of heat through a material by the movement of the material itself. What is Convection ???

11. The transfer of heat in a liquid is demonstrated below: cold water coloured crystal cold water sinks hot water rises coloured crystal dissolves When the hot water rises, heat energy is carried from one place to another. This movement of heat is called convection .

12. The transfer of heat in a gas is demonstrated below: The movements of the hot and cold air set up a convection current . glass chimney smoke particles smouldering paper box glass front convection air

13. An Explanation for Convection When a substance is heated, it expands and its volume increases. Density decreases. HOT liquid/gas becomes less dense than COLD liquid/gas hot and less dense parts of the liquid or gas will rise while the surrounding cooler and denser parts will sink Convection currents are set up which transfer heat from the hotter regions to the cooler regions. cooler water is more dense and falls hotter water is less dense and rises

14. Uses and Effects of Convection Applications of convection in water: hot water system electric kettle hot water tank boiler expansion pipe cold water tank cold water sinks cold water sinks water hot water rises

15. Uses and Effects of Convection Applications of convection in air: glider air-conditioner heater cold air warm air cold air hot air

16. Uses and Effects of Convection Sea breeze cooler air takes the place of the hotter air cooler air COOLER HOTTER hotter air rises

17. Uses and Effects of Convection Land breeze cooler air takes the place of the warmer air warm air rises COOLER WARMER cooler air falls

20. 15.3 Radiation Definition: Radiation is the transfer of energy through a vacuum in the form of waves. What is Radiation ???

21. All hot objects give out energy as radiation. The radiation moves in all directions. sun radiation radiation radiation Radiation itself is not hot, but when absorbed, is changed to heat.

22. Heat from a Fire The fire warms the boy because most of the heat reaches him by radiation. Very little heat comes from conduction or convection.

23. Absorption of Heat All objects are able to absorb radiation. Both the black (or dull) flask and the white (or shiny) flask absorb heat, but the black flask absorbs heat faster. air inside

24. Radiation of Heat All hot objects are able to radiate heat. Both the black (or dull) flask and the white (or shiny) flask radiate heat, but the black flask radiates heat faster, and cools more quickly than the white flask. hot water inside

26. Applications of Absorbers and Radiators of Heat Uses of absorbers and radiators of heat: white clothes solar water heater hot water container fuel storage tank refrigerator

27. 15.4 More Applications of Heat Transfer Keeping Food Warm A plastic food box helps to reduce heat loss in three ways: 1) Conduction – styrofoam is a poor conductor of heat 2) Convection – box is covered by a lid 3) Radiation – white surface is poor absorber and good reflector of heat

29. Design of Spacesuits Temperatures in space range from very hot to very cold depending on whether they are facing the sun. helmet white outer layer layers of insulating material As astronauts on space missions have to work outside the space shuttle, their spacesuits must be able to keep their bodies at a comfortable temperature.

30. Keeping Buildings in Singapore Cool Some ways to reduce heat transfer: concrete air-conditioning double-glazing glass walls