Download 5.1 The Nature of Heat

Chapter 6 Controlling Heat Transfer
6.1 Absorbing and Losing Heat
Science 14 and 10-4
with Mrs. M
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
Water Can Take the Heat
• 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
Oceans moderate climate
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•
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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 Capacity
https://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
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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 #1a
Use 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 noncombustible
• 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=GjMsV4V
sJew
• Until 3:45
• https://www.youtube.com/watch?v=BIHpsyuy
V4I 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?
How does a vacuum bottle reduce
convection, conduction, radiation?
• 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
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