1. Heat Transfer

2. Heat Transfer Heat always moves from a warmer place to a cooler place.
Hot objects in a cooler room will cool to room temperature.
Cold objects in a warmer room will heat up to room temperature.

3. Question
If a cup of coffee and an ice cube were left on the table in this room what would happen to them? Why?
Answer
The cup of coffee will cool until it reaches room temperature. The ice will melt and then the liquid will cool to room temperature.

4. HEAT TRANSFER METHODS
Conduction
Convection
Radiation

5. CONDUCTION
Heat travels along a substance from molecule to molecule (between two materials that touch each other)
Good conductors (silver, copper, gold)
Poor conductors ( glass, paper, Styrofoam)

6. Conduction
When you heat a metal strip at one end, the heat travels to the other end.
As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat. We call this?

7. Metals are different
The outer e_______ for metal atoms drift, and are free to move.
lectrons
When the metal is heated, this ‘Sea of electrons’ gain k_____ energy and transfer it throughout the metal.
inetic
Insulators, such as w___ and p____, do not have this ‘Sea of electrons’ which is why they do not conduct heat as well as metals.
ood
lastic

8. Why does metal feel colder than wood, if they are both at the same temperature?
Metal is a conductor, wood is an insulator. The metal conducts the heat away from your hands, the wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.

9. CONDUCTION EXAMPLES water heating on an electric stove
hot sand touching your feet
touching a stove and being burned
ice cooling down your hand
boiling water by thrusting a red-hot piece of iron into it

10. CONVECTION transfer of energy as it is carried through a liquid or gas
heat transfer by a circulation of rising warm air (less dense) and sinking cooler air (denser).
“Hot air rises” the more dense air sinks forcing the less dense air upward

11. The particles spread out and become less dense.
Heating fluids
What happens to the particles in a liquid or a gas when you heat them?
The particles spread out and become less dense.
What is a fluid?
A liquid or gas.

12. Fluid movement
Cooler, more d____, fluids sink through w_____, less dense fluids.
ense
armer
In effect warmer liquids and gases r___ up.
ise
Cooler liquids and gases s___.
ink

13. Water movement Cools at the surface Convection current Hot water rises
Cooler water sinks

14. Why is it windy at the seaside?

15. Where is the freezer compartment put in a fridge?
Cold air sinks
Where is the freezer compartment put in a fridge?
Freezer compartment
It is warmer at the bottom, so this warmer air rises and a convection current is set up.
It is put at the top, because cool air sinks, so it cools the food on the way down.

16. CONVECTION EXAMPLES
macaroni rising and falling in a pot of heated water
heat rising from a chimney
an old-fashioned radiator (creates a convection cell in a room by emitting warm air at the top and drawing in cool air at the bottom)

17. RADIATION
Carries energy away from the hot object and causes it to cool down
The movement of heat in a wave-like motion through an empty space

18. ? RADIATION 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 ?

19. Radiation travels in straight lines True/False
Radiation requires particles to travel
Radiation travels at the speed of light

20. RADIATION EXAMPLES sunlight heat from toaster heat from a light bulb
heat from a fire
heat from anything else which is warmer than its surroundings

21. hot water rises and cold water sinks
CONVECTION

22. stir frying vegetables
CONDUCTION

23. a spoon in a cup of hot soup becomes warmer
CONDUCTION

24. grilling hamburgers over a charcoal flame
RADIATION

25. hot air balloon rises
CONVECTION

26. you feel the heat from a campfire
RADIATION

27. a raw egg begins to fry as it hits a heated frying pan
CONDUCTION

28. CONVECTION
Heated air rises, cools, then falls.  Air near heater is replaced by cooler air, and the cycle repeats.

29. boiling potatoes
CONDUCTION

30. microwave oven
RADIATION

31. Propane Heater
RADIATION

32. basement is cooler than the attic
CONVECTION

33. radiator warms your hands
CONVECTION

34. a person takes a warm bath
CONDUCTION

35. heat from a light bulb
RADIATION

36. hot pan is cooled by running it under cold water
CONDUCTION

37. you get sunburned
RADIATION

38. warm water at the surface of the swimming pool
CONVECTION

39. ironing a shirt
CONDUCTION

40. wind currents
CONVECTION

41. ANSWER KEY hot water rises and cold water sinks - Convection
stir frying vegetables - Conduction
a spoon in a cup of hot soup becomes warmer - Conduction
grilling hamburgers over a charcoal flame - Radiation
hot air balloon rises - Convection
you feel the heat from a campfire - Radiation
a raw egg begins to fry as it hits a heated frying pan - Conduction
Heated air rises, cools, then falls.  Air near heater is replaced by cooler air, and the cycle repeats. - Convection
boiling potatoes in water –Conduction (water to potato)
microwave oven - Radiation
propane heater - Radiation
basement is cooler than attic - Convection
radiator warms your hands - Convection
a person takes a warm bath - Conduction
heat from a light bulb - Radiation
hot pan is cooled by running it under cold water - Conduction
you get sunburned - Radiation
warm water at the surface of the swimming pool - Convection
Ironing a shirt - Conduction
wind currents - Convection