Chapter 6 Controlling Heat Transfer6.1 Absorbing and Losing Heat

Science 14 and 10-4with Mrs. M

Specific Heat CapacityCan’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

• Heat absorption: 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

Water Can Take the Heat

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

Fire walkers• Socks make their feet sweat before performing

the walk. How might this help to protect their feet from burning? https://www.youtube.com/watch?v=-iBFwpKV6ak

Lab Report• Heat absorption 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 heating?

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 better 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 better? Why?

Air vs. Water Heat Capacityhttps://www.youtube.com/watch?v=hyPLusD-tyM

6.2 Keeping Heat at Home

• During winter, Canadian houses lose heat because hot air escapes to the cold outside

• Insulation can help this problem

Conductors vs Insulators

• Metal• Ceramic• Electrical wire

• Glass• Wood• Plastic• Fabrics• Reflective foil

Conductors vs Insulators

• Metal• Ceramic• Electrical wire

• Glass• Wood• Plastic• Fabrics• Reflective foil

Why wrap food in aluminum/tin foil?

Why do welders need equipment?

6.2 Insulation

• Insulation slows heat transfer• R-value is a measure of how well an insulating

material slows heat transfer• High R-value means better insulation

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 = 3.96 + 7.50 = R-11.46

Check Your Understanding

• Page 119 #1aUse Table 6.2 on page 111 to help you calculate

the R-values of the following insulation materials:

a) 25 mm of air space + 25 mm of expanded polystyrene

Cavity Walls• Walls often have a cavity of air in between the

layers• This air gap can be filled with insulation to

eliminate convection currents within walls

What has a higher R-value?

• Double wall

• Double wall with insulation

Check Your Understanding

• Page 119 #1

Guest Speaker: Firefighter

Facts about fire:• Can be caused by overheating electrical wires,

kitchen fires, gas leaks

• Houses vaporize (flame over) at 1000°C so firefighters need to get out

Firefighter Safety

• Firefighters are most likely to burn their ears, chin, and neck

• Protective gear is made of three layers– Kevlar: prevent injection (glass, needles)– Fire resistant: prevent heat transfer– Micro-fiber: waterproof prevents absorption

• Visor melts at 700°C to signal it is time to get out

Firefighter Equipment

• Boots, pants, coat, helmet, gloves, mask

Cool Facts• Firefighter equipment is both expensive and

heavy

Pop Can House

Controlling Heat Transfer

• How do pizza deliveries keep your pizza warm?

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

Why do builders put more insulation in attics than in walls?

Asbestos

• Asbestos fibres are strong, durable and non-combustible

• Used widely in the ‘50s - ‘70s• People in construction, maintenance, and

renovation must be careful

Asbestos• Good for reinforcing, insulating, fire-proofing• No risk if fibres are enclosed or tightly bound

in a product, (asbestos siding or floor tiles) • Asbestos poses health risks only when fibres

are present in the air that people breathe

Asbestos

• https://www.youtube.com/watch?v=GjMsV4VsJew

• Until 3:45

• https://www.youtube.com/watch?v=BIHpsyuyV4I Thermal sensors

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 foundations, and exhaust emissions

Vacuum Bottle: Thermos

• Insulated to keep your food or beverage warm• Insulation slows heat transfer• How does it work?

• Double glass jar (similar to double pane window)• Partial vacuum from removing

some air between glass jars• Reflective coating• Rubber/plastic outer case• Insulated cap

How does a vacuum bottle reduce convection, conduction, radiation?

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 mitts

6.3 Keeping Warm

• Multiple layers keep you warm in the winter

Polar bears have hollow guard hairs

Air is an insulator

Chapter 6 Review

• Key Term Definitions or Reviewing Key Terms• #2, 4, 7, 10, 12, 13