1. YOU WALK INTO THE BATHROOM IN YOUR BARE FEET. THE TEMPERATURE IN THERE IS 23C. YOU STEP ONTO THE TILE FLOOR, AND IT FEELS VERY COLD. QUICKLY, YOU STEP ONTO THE THROW RUG IN FRONT OF THE SINK, AND THE RUG FEELS WARMER. 1. 1.Is the floor really colder than the rug? 2. 2. Why do they seem to be at different temperatures when your bare feet touch them?

2. HEAT TRANSFER Chapter 10

3. HEAT TRANSFER The transition (transfer) of heat (thermal) energy from a hotter to a cooler object/substance The transition (transfer) of heat (thermal) energy from a hotter to a cooler object/substance Hot objects in a cooler room will cool to room temperature Hot objects in a cooler room will cool to room temperature Cold objects in a warmer room will heat up to room temperature Cold objects in a warmer room will heat up to room temperature 3 ways to transfer heat: Conduction, Convection, and Radiation 3 ways to transfer heat: Conduction, Convection, and Radiation

4. QUESTION If a cup of coffee and a red popsicle were left on the table in this room what would happen to them? Why? If a cup of coffee and a red popsicle were left on the table in this room what would happen to them? Why? The cup of coffee will cool until it reaches room temperature. The popsicle will melt and then the liquid will warm to room temperature. The cup of coffee will cool until it reaches room temperature. The popsicle will melt and then the liquid will warm to room temperature.

5. CONDUCTION Occurs when heat passes through solids Occurs when heat passes through solids Occurs when two substances come in direct contact Occurs when two substances come in direct contact Heat keeps flowing until both objects are equally hot Heat keeps flowing until both objects are equally hot Conductors conduct heat (metals) Conductors conduct heat (metals) Insulators do not conduct heat (wood, rubber) Insulators do not conduct heat (wood, rubber)

6. WHY DOES METAL FEEL COLDER THAN WOOD, IF THEY ARE BOTH AT THE SAME TEMPERATURE? Metal is a conductor, wood is an insulator. Metal conducts the heat away from your hands. Wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal. Think about a Metal vs Wooden Spoon in hot soup….

7. CONDUCTION

8. CONVECTION Occurs when heat passes through fluids (gasses and liquids) Occurs when heat passes through fluids (gasses and liquids) Liquids and gasses move apart when heated Liquids and gasses move apart when heated Less dense hot particles move up and more dense cool particles move down- (convection current) Less dense hot particles move up and more dense cool particles move down- (convection current) Convection currents continue in a circular cycle Convection currents continue in a circular cycle

9. CONVECTION What happens to the particles in a fluid (liquid or a gas) when you heat them? The particles spread out (because they are moving faster now) and become less dense. This affects fluid movement.

10. WATER MOVEMENT Hot water rises Cooler water sinks Convection current Cools at the surface Ex: Boiling water in a pan… Question: how does a lid affect things?…

11. CONVECTION

12. THE THIRD METHOD OF HEAT TRANSFER How does heat energy get from the Sun to the Earth? There are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection. ? RADIATION

13. RADIATION Heat transferred thru waves Heat transferred thru waves Does not need a medium to transfer heat Does not need a medium to transfer heat Heat is “given off” Heat is “given off” Example: Sun heating the pavement (or you) during a summer day Example: Sun heating the pavement (or you) during a summer day

14. RADIATION QUESTIONS Why are houses painted white in hot countries? White reflects heat radiation and keeps the house cooler. Why are shiny foil blankets wrapped around marathon runners at the end of a race? The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold.

15. CONVECTION QUESTIONS Why are boilers placed beneath hot water tanks in people’s homes? Hot water rises. So when the boiler heats the water, and the hot water rises, the water tank is filled with hot water. Why does hot air rise and cold air sink? Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air.