Grade 7 Science Unit 2

1. Grade 7 Science Unit 2 Heat is transferred from one place to another by three different processes. Chapter 6

2. Heat Transfer • Heat transfers from a hot object to a cold object. • Heat moves NOT cold • Something cold is really just something less hot

3. 3 Types of Heat Transfer • Conduction • Convection • Radiation

5. 1. Conduction • Particle movement: • the particles in an object vibrate in place but collide with neighbouring particles passing kinetic energy to them. • State(s) in which it occurs: • Can happen in Solid, liquid and gas • Best in solid’s worse in gases

6. The particles stay in position!

7. Examples of conduction • Cooling on a stove • Ice packs • Can you think of other examples?

8. Conduction mini experiment • Comparing conduction • Do some materials conduct better than others?

9. 2. Convection • Particle movement: • When heated the particles gain energy, spread out, become less dense and rise. As it cools, the particles lose energy, get closer together, become more dense and sink. • State(s) in which it occurs: • Can happen in liquids and gas • Not in Solids!

11. Examples of Convection • Boiling water on the stove • Radiators • Can you think of other examples?

12. Convection Demonstration • convection currents using a convection box or convection tube

13. 3. Radiation • Particle movement: • No particles!! • electromagnetic waves carry energy from a source to another object. • State(s) in which it occurs: • Any or none! No state necessary • Can occur in the vacuum of space

15. Examples of Radiation • Fireplace • Sunlight

16. All 3 can happen at the same time!

17. 3 ways radiant energy transfers • Reflect: bounce of shiny, smooth surfaces • Absorb: Taken in by rough, dull coloured surfaces (gets warmer) • Transmit: Moves through glass, plastic, paper.

19. Interactive: • http://www.pbslearningmedia.org/asset/lsps07_int_heattransfer/ • Online Practice: • http://www.webquest.hawaii.edu/kahihi/puzzles/energytransfer/index.php

21. Core Lab Activity! Activity 6-1D “Absorb That Energy” Page 184

22. Home Heating! • Brainstorm: How do we heat our homes?

23. Home Heating Technology • Wood stove • Electric Heaters • Oil Furnace • Air to Air Heat Pump • Geothermal • Solar

25. Oil furnace

26. Hot-water radiation

27. Air to air Geothermal

28. Core STSE “Heat Pumps: An Alternative Way to Heat Homes”

29. Section Review Questions • Page 191 Q’s: 1, 2, 3, 4 & 9

30. Conductors Vs. Insulators

31. Thermal conductors • Allows heat to travel • Cookware – warms your food • Car Radiator – warms your car

32. Thermal insulators • Keeps Items Warm! • Animal Fur – animals/humans • Sod – houses in the past • Fibreglass – houses in the present • Thermos - food

33. How does a thermos work? • A vacuum exists between the layer • No particles means little heat transfers!

34. Try it out! • Interactive mini-lab • http://www.bbc.co.uk/schools/scienceclips/ages/8_9/keeping_warm.shtml

35. Section Review Questions • Page 205 Q’s: 1, 2& 9

36. Heat Vs. Temperature • Heat: The energy which is transferred from hotter substances to colder ones. • Note: cold doesn’t move, heat does! • Heat: the total energy • Temperature: the average energy

38. Specific Heat Capacity • Specific Heat Capacity: Measures the amount of heat transferred • The amount of heat needed to raise the temperature of 1.00 g of a substance by 1.00˚C.

39. Specific Heat Capacity • High specific heat capacity takes a lot of heat to warm up • A lot of heat transfers • Low specific heat capacity takes only a little heat to warm up • Only a little heat transfers

40. Specific heat capacities of various substances • Don’t Need to memorize these!

41. Which has a higher Specific Heat capacity? • Water or soil? • Think about it: • On a hot day which warms up more quickly – the water or sand?

42. Which has a higher Specific Heat capacity? • Water or soil? • Soil! • Think about it: • On a hot day which warms up more quickly – the water or sand? • Sand! It cools more quickly as well

43. Question 1 • Why do metal objects often feel colder than the surrounding air temperature?

44. Question 1 • Why do metal objects often feel colder than the surrounding air temperature? Not because the metal is colder • Metal has a low specific heat capacity, it will quickly absorb heat! • The heat from our hands is transferred to the metal quickly • This makes our fingers cold – the metal feels cold!

45. Question 2 • Why does a piece of aluminum foil feel cool after taken out of the oven for only minutes?

46. Question 2 • Why does a piece of aluminum foil feel cool after taken out of the oven for only minutes? • The aluminum has a low specific heat capacity. • It quickly takes in heat, but also loses it quickly • It doesn’t take much heat to warm it up so it will lose that small amount of heat quickly

47. Question 3 • Why should you be cautious when eating an apple pie which has been taken from the oven for twenty minutes?

48. Question 3 • Why should you be cautious when eating an apple pie which has been taken from the oven for twenty minutes? • The apple pie has a high specific heat capacity. • It takes a lot of heat to warm it up so it will take a long time to lose all of that heat!

49. Interactive • comparing specific heat interactive: • http://oceanservice.noaa.gov/education/pd/oceans_weather_climate/media/specific_heat.swf

50. Discussion: Sea and Land Breeze