Chapter 6 Controlling Heat Transfer 6.1 Absorbing and Losing Heat. Science 14 and 10-4 with Mrs. M

Transcription

1 Chapter 6 Controlling Heat Transfer 6.1 Absorbing and Losing Heat Science 14 and 10-4 with Mrs. M

2 Specific Heat Capacity Can t take the heat? Get out of the kitchen! Just kidding, water can take the heat Water can absorb a lot of heat without raising its temperature a lot It takes a lot more heat energy to increase the temperature of water Water has a HIGH specific heat which means a LOW temperature compared to other substances

3 Water Can Take the Heat Heat absorp:on: the rate at which materials absorb heat Specific heat capacity: measures a substance s ability to absorb or lose heat Water has a high specific heat so it can take on a lot of heat energy without increasing it s temperature too much

4 Oceans moderate climate Oceans store thermal energy (heat) Water can absorb heat on a hot day Water can release heat on a cool day Water s specific heat capacity is larger than that of oil, sand, or metal

5 Fire walkers Socks make their feet sweat before performing the walk. How might this help to protect their feet from burning? hqps:// ibfwpkv6ak

6 Lab Report Heat absorpzon and specific heat capacity There are equal amounts of water, vegetable oil, and vinegar in beakers on a hot plate. If all are given the same amount of heat, which will heat up fastest? Which will stay hot the longest? Analysis: Considering water s specific heat capacity is 4.19 J/g C and oil s is 1.97 J/g C, why do you think that you saw the difference in heazng?

7 Check Your Understanding Page 110 #3. Why does water at a beach feel cooler than sand during the day and warmer at night? #4. Use your knowledge of specific heat capacity to explain why water is a beqer coolant than vegetable oil. Relate your knowledge of specific heat capacity to coolant in a car radiator. #5. You plan to make French fries. It s best to use very hot oil with a higher or lower specific heat capacity beqer? Why?

8 Air vs. Water Heat Capacity hqps:// tym

9 6.2 Keeping Heat at Home During winter, Canadian houses lose heat because hot air escapes to the cold outside InsulaZon can help this problem

10 Conductors vs Insulators Metal Ceramic Electrical wire Glass Wood PlasZc Fabrics ReflecZve foil

11 Conductors vs Insulators Metal Ceramic Electrical wire Glass Wood PlasZc Fabrics ReflecZve foil

12 Why wrap food in aluminum/zn foil?

13 Why do welders need equipment?

14 6.2 InsulaZon Insula:on slows heat transfer R- value is a measure of how well an insulazng material slows heat transfer High R- value means beqer insulazon

15 R- value The total R- value is the sum of the R- values of each material used Example: What is the total R- value if you have 25mm of expanded polystyrene and rigid urethane? expanded polystyrene 3.96 rigid urethane 7.50 Total = = R

16 Check Your Understanding Page 119 #1a Use Table 6.2 on page 111 to help you calculate the R- values of the following insulazon materials: a) 25 mm of air space + 25 mm of expanded polystyrene

17 Cavity Walls Walls olen have a cavity of air in between the layers This air gap can be filled with insulazon to eliminate conveczon currents within walls

18 What has a higher R- value? Double wall Double wall with insulazon

19 Check Your Understanding Page 119 #1

20 Facts about fire: Guest Speaker: Firefighter Can be caused by overheazng electrical wires, kitchen fires, gas leaks Houses vaporize (flame over) at 1000 C so firefighters need to get out

21 Firefighter Safety Firefighters are most likely to burn their ears, chin, and neck ProtecZve gear is made of three layers Kevlar: prevent injeczon (glass, needles) Fire resistant: prevent heat transfer Micro- fiber: waterproof prevents absorpzon Visor melts at 700 C to signal it is Zme to get out

22 Firefighter Equipment Boots, pants, coat, helmet, gloves, mask Cool Facts Firefighter equipment is both expensive and heavy

23 Pop Can House

24 Controlling Heat Transfer How do pizza deliveries keep your pizza warm?

25 Windows and Doors Leak Heat How do we keep the heat in? Older houses have storm windows or storm doors. Two doors help keep heat in. Today we use an extra glazing on glass windows Weather stripping

26 Why do builders put more insulazon in aocs than in walls?

27 Asbestos Asbestos fibres are strong, durable and non- combuszble Used widely in the 50s - 70s People in construczon, maintenance, and renovazon must be careful

28 Asbestos Good for reinforcing, insulazng, fire- proofing No risk if fibres are enclosed or Zghtly bound in a product, (asbestos siding or floor Zles) Asbestos poses health risks only when fibres are present in the air that people breathe

29 Asbestos hqps:// v=gjmsv4vsjew UnZl 3:45 hqps:// v=bihpsyuyv4i Thermal sensors

30 How do police use infrared heat to find grow ops? Officers are trained to look for infrared hot spots on walls and windows, unusually warm foundazons, and exhaust emissions

31 Vacuum BoQle: Thermos Insulated to keep your food or beverage warm Insula:on slows heat transfer How does it work?

32 How does a vacuum bo.le reduce convec2on, conduc2on, radia2on? Double glass jar (similar to double pane window) ParZal vacuum from removing some air between glass jars ReflecZve coazng Rubber/plasZc outer case Insulated cap

33 6.3 Keeping Cool People in deserts wear more clothes to minimize heat transfer You protect your hands from the oven s heat using oven miqs

34 6.3 Keeping Warm MulZple layers keep you warm in the winter

35 Polar bears have hollow guard hairs Air is an insulator

36 Chapter 6 Review Key Term DefiniZons or Reviewing Key Terms #2, 4, 7, 10, 12, 13