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Introduction
Introduction
 Energy Transfer – the transfer of energy from one
body to another
Chapter 5: Heat and Heat Transfer
Introduction
 Snow ball activity!
 On looseleaf:
 What do you already know about heat?




What is heat?
How does heat transfer from one object to another?
Why is controlling heat transfer important for engines
and technological devices?
Why is controlling heat transfer important for your
own survival?
Introduction
 Terminology
 Heat Energy vs. Thermal Energy

These two terms are essentially the same thing. They can be
used interchangeably.
Introduction
 What causes heat?
 Where does it come from and why?
 For over a century, scientists hotly debated the answers
to these questions as they worked to develop modern
heat theory.
Introduction
 In a pre-match society, starting a fire was not the simple
task it is today.
 In many early societies, people who could start fires easily
were admired, often revered. If it was your job to keep the
fire going, letting it go out was considered a grievous
wrong.
5.1 The Nature of Heat
 Friction Theory
 when two surfaces are rubbed together, the parts that
touch resist movement
 This resistance is friction
 Count Rumford used observations about friction to
change the way scientists look at heat
5.1 The Nature of Heat
 Benjamin Thomson was an engineer and scientist who
lived in the Thirteen Colonies at the time of the
American Revolution.
 Because he stayed loyal to Britain, many Americans
considered him a traitor.
 British loyalists, however, considered him a hero.
 Thomson was given the title of Count Rumford to
reward him for his loyalty to Britain.
5.1 The Nature of Heat
 Rumford was an engineer/scientist who was hired to
manufacture cannons in Munich, Germany.
 During this project, one worker carelessly touched a
rod being used to bore a hold through a piece of metal.
His hand was seriously burned.
 In the late 1700s, Count Rumford observed that heat
was created when metal cut metal.
 This heat results from friction!
5.1 The Nature of Heat
 Have you ever watched popcorn popping in an air
popper?
 The random, dancing motion of the kernels is easy to
observe.
 But what causes this motion?
5.1 The Nature of Heat
 A similar type of motion is occurring in a glass of
water.
5.1 The Nature of Heat
 Robert Brown – the first to realize this similarity
 During the 1800s he was using a microscope to observe
pollen grains in a drop of water.
 He noticed that although the microscope was quite still,
the pollen grains bounced around.
 When he increased the temperature of the water, the
motion increased.
 This motion has become known as Brownian Motion
http://www.microscopy-uk.org.uk/dww/home/hombrown.htm
5.1 The Nature of Heat
 Making the observation was easy.
 But how can we explain it?
5.1 The Nature of Heat
 At first, Brown thought that the pollen grains were alive.
 Later he reasoned that water must be composed of tiny
unseen particles. These particles are in constant,
vibrating motion.
 The motion of the pollen grains must be caused by
collisions between the pollen grains and the other
unseen particles. (Brown was unsure of what the
particles were)
 Later, his evidence helped develop the kinetic molecular
theory.
5.1 The Nature of Heat
 The concept of heat is commonplace; what causes heat
is fairly abstract.
 Technically, heat is defined as the transfer of energy
from one substance to another and is identified by a
difference in temperature.
 An object does not possess heat. Rather, an object
possesses thermal energy and can lose that energy in
the process of heat loss.
5.1 The Nature of Heat
 It is a common misconception to think of heat as a
thing rather than a process.
 This probably stems from the original caloric
definition of heat.
 Scientists thought that something measurable left an
object when it got colder.
 Recall that Rumford was able to gain a scientific
understanding of heat through observations of
friction.
5.1 The Nature of Heat
 Before Rumford, scientists thought heat was a fluid
they called caloric.
 Rumford did not replace the caloric theory. Rather, he
demonstrated an inconsistency in the theory.
 Two later British scientists — Sir Humphry Davy and
James Prescott Joule took Rumford’s ideas to the next
step.
5.1 The Nature of Heat
 Davy, an English chemist,
designed demonstrations to
disprove the caloric theory.
 He rubbed ice and other
solids with low melting
points together to show that
they would melt with heat
from friction.
5.1 The Nature of Heat
 Joule determined the mechanical
equivalent of heat by measuring the
change in temperature produced by
friction.
 Working in imperial measure, he
found that, on average, a weight of 772
pounds falling through a distance of
one foot would raise the temperature
of one pound of water by 1°F.
 In addition, Joule’s investigations
showed that heat is produced by
motion, contradicting the caloric
theory.
5.1 The Nature of Heat
 We can relate this to the calorie, which is related to
food energy.
 The calorie is a unit of energy. One calorie is the
amount of energy needed to raise 1 gram of water by
1°C.
 Other units of energy are the joule — named after
James Prescott Joule and the British Thermal Unit
(BTU).
 The BTU is used in Canada to rate thermal output of
stoves, ovens, and barbecues.
5.1 The Nature of Heat
 Mysterious Motion
 P. 84
5.1 The Nature of Heat
5.1 The Nature of Heat
 Practice!
 Check Your Understanding p. 85
5.2 Heat and Temperature
 The modern theory of heat began with Robert Brown
 He was the first to suggest that the energy that came
with heat – thermal energy – was related to the
motion of unseen particles of a substance.
 But, what are these unseen particles? What causes the
motion?
5.2 Heat and Temperature
 Recall the Particle Theory of Matter:
 All matter is composed of tiny, unseen particles
 These unseen particles are in constant, random motion.
5.2 Heat and Temperature
 Kinetic – means movement
 Kinetic Art – art that moves (i.e. Mobiles)
 Kinetic Energy – a form of energy associated with
motion
 It is a measure of the amount of motion particles have.
 We can use kinetic energy to explain the difference
between heat and temperature
5.2 Heat and Temperature
 A molecule can have three different forms of
movement:
 Vibrational — molecules “vibrate” back and forth
 Rotational — molecules spin and rotate
 Translational — molecules bump and move around
5.2 Heat and Temperature
 The motion of particles can be compared to bumper
cars!
5.2 Heat and Temperature
 Like bumper cars, atoms and molecules collide with
each other at different speeds.
 All particles have different kinetic energies.
5.2 Heat and Temperature
 So what is the difference between heat and
temperature?
 Temperature – the average of ALL kinetic energies of
all particles in an object
 Heat – the sum of all kinetic energies of all particles in
an object
5.2 Heat and Temperature
 Example:
25 mL
Temperature: 30°C
Less kinetic energy
100 mL
Temperature: 30°C
More kinetic energy
5.2 Heat and Temperature
 Because temperature is a measure of how fast
molecules are, and because molecules slow as they get
colder, the coldest possible temperature is finite!
Particles truly stop moving at absolute zero. Absolute
zero is -273.15°C
 The lowest artificial temperature achieved to date is
0.003°K. The highest is estimated at 100 000 000°K and
was from a nuclear blast.
5.2 Heat and Temperature
 There are more temperature scales than Celsius and
Fahrenheit. The Kelvin scale (K) starts at absolute zero
and rises in degrees equal in magnitude to Celsius
degrees.
 Other scales include the Rankine scale and the
International Temperature Scale.
5.2 Heat and Temperature
 Practice!
 Check Your Understanding p. 87
5.3 Transfer of Heat
 There have been many predictions about when Earth
will end.
 Fear of Y2K computer problems brought excitement to
New Year’s Eve 2000.
 As we study heat transfer, we will learn about another
proposed end to the universe 
5.3 Transfer of Heat
 Forms of Heat Transfer
 Heat flows from hot to cold.
 The flow continues until both objects are at the same
temperature.
 But what is really happening? How does thermal energy
transfer from one object to another?
5.3 Transfer of Heat
 Conduction
 Molecules placed on a hot burner will vibrate quickly.
 They have more kinetic energy than the molecules in a
cooler location (a cool pot).
 Contact between the pot and the burner causes the
molecules of the hot burner to collide with the slower
molecules of the cool pot.
 These collisions result in a transfer of kinetic energy.
5.3 Transfer of Heat
 The molecules of the cooler pot start to vibrate faster,
gaining kinetic energy.
 The molecules of the hot burner vibrate slower, losing
kinetic energy.
 This transfer of heat by contact is called conduction.
5.3 Transfer of Heat
 Thermal conductivity and electrical conductivity are
related.
 Substances that conduct electricity will also tend to be
good thermal conductors.
 Metal is a good example of this. Conversely, glass and
wood are poor thermal and poor electrical conductors.
5.3 Transfer of Heat
 Convection
 If you hold your hand above a hot burner of a stove, you
will feel a warm current of air.
 Why?
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
Heat is transferred, by conduction, from the hot burner to the
air molecules touching the burner.
These air molecules gain kinetic energy, vibrate faster, and get
farther apart.
5.3 Transfer of Heat
 The warmer molecules are farther apart than the cool
air molecules, so the warm air is less dense than the
cool air around it.
 This causes the warm air to rise, creating the warm
current that we feel.
 Cool, denser air rushes to take the place of the warm
air.
5.3 Transfer of Heat
 Because of continuous air flow, all the air in the room
will become warmer.
 This transfer of heat by movement is called
convection.
5.3 Transfer of Heat
 Radiation
 Picturing a hand that is close to the side of a burner, but
not above the burner can help us explain radiation.
 The front of the hand is not being heated by conduction
or convection.
 There is no contact with the burner and convection
currents of warm air would rise away from the hand.
5.3 Transfer of Heat
 The front the hand is being heated by radiation.
 Radiation is produced by vibrating electrons, which
are tiny particles present in all atoms.
 This vibration makes a wave called an electromagnetic
wave or infrared radiation wave.
 These waves are similar to the waves your hand can
create when it vibrates in calm water.
 Waves or ripples run away from your moving hand.
5.3 Transfer of Heat
 Infrared radiation waves travel from the burner.
 They strike the hand and transfer heat energy to the
molecules in the hand.
 This causes molecules in the hand to vibrate faster.
5.3 Transfer of Heat
 On a sunny day, most of the heat that you feel is the
result of infrared radiation from the Sun.
 Infrared radiation is one form of electromagnetic
radiation. Other forms include ultraviolet radiation,
radio waves, visible light waves, and X rays.
 Electromagnetic radiation travels in waves. Each type
of electromagnetic radiation has a specific wavelength
and moves through the vacuum of space.
5.3 Transfer of Heat
5.3 Transfer of Heat
 Did You Know?
 Hot objects warm cool ones until their temperatures are
the same.
 Some people believe this will happen to the universe.
 According to the theory, the temperature of the entire
universe will eventually be the same.
 When this happens, heat will no longer transfer.
 Without a source of energy, life will be impossible!
 This prediction is called the “Heat Death of the
Universe.”
5.3 Transfer of Heat
 Practice!
 Check Your Understanding p. 91
5.4 Heat Transfer in Nature
 Convection causes many weather phenomena, such as
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winds.
Many cottages are on the shores of lakes, where
convection currents keep the cottages cool in the
daytime and warmer at night.
In the evening, the air over the water cools more slowly
than the air over the land.
Warm air from over the water rises and moves toward
the land, keeping it warm.
During the day, cool air from the lake moves towards
the warm land.
5.4 Heat Transfer in Nature
 Sea and Land Breezes
 Recall: warm air rises, and cool air sinks
 The circular movement that results is called convection.
 All winds start with convection currents.
5.4 Heat Transfer in Nature
 Land and sea breezes are convection currents of air
that occur near a shoreline.
 They are both created by differences in temperature
near the surface of the Earth.
5.4 Heat Transfer in Nature
 On a sunny day, radiant heat from the Sun strikes
Earth’s surface.
 Heat is absorbed by land and water. But land and
water heat at different rates.
 Land heats quickly, but also cools quickly.
 Water heats slowly and takes longer to cool.
5.4 Heat Transfer in Nature
5.4 Heat Transfer in Nature
 How Oceans Help to Moderate Climates
 Oceans are capable of storing large amounts of thermal
energy.
 This prevents the area around them from having
extreme temperature changes.
 Oceans moderate the climate of land areas near them.
 This means they prevent the area from becoming too
hot or too cold.
 But how???
5.4 Heat Transfer in Nature
 In cool weather, an ocean can release great amounts of
heat without cooling much itself.
 Even during very hot or very cold days, and as seasons
change, the temperature of oceans remains constant.
 As the sun warms the air above the ocean, heat flows
from the air into the water, cooling the air.
 When the temperature of the air above the ocean
cools, heat flows from ocean to air and warms the air.
5.4 Heat Transfer in Nature
 We could say that oceans prevent land near them from
getting very warm or very cold.
 Because of this, coastal cities (like Vancouver) have
moderate climates.
5.4 Heat Transfer in Nature
5.4 Heat Transfer in Nature
 Practice!
 Check Your Understanding p. 97
 Heat Transfer Review (worksheet)
 Midpoint Review (worksheet)
5.5 Heat Transfer and Technologies
 Many household technologies either transfer or
prevent the transfer of heat through conduction,
convection or radiation.
 That is why metal cooking pots have hard plastic or
wooden handles.
 What other techniques are used to handle hot
food?
5.5 Heat Transfer and Technologies
 Stoves
 Most cooks want to control how food is heated.
 Consider the following: heating soup on a stove top.
 The pot is heated by conduction through contact with
the burner.
 The soup at the bottom of the pot heats up first through
conduction.
5.5 Heat Transfer and Technologies
 Heated soup rises to the top, because it is less dense.
 Colder soup near the top of the pot flows to the bottom
because it is more dense.
 This causes a circular motion (aka convection currents)
and allows the entire pot of soup to heat to a uniform
temperature.
5.5 Heat Transfer and Technologies
 Ovens
 When an oven is turned on, convection currents move
heat inside the oven.
 Air at the bottom of the oven is heated by burning gas
or an electric element.
 The heated air becomes less dense and rises to the top
of the oven.
 The cooler air sinks to the bottom.
5.5 Heat Transfer and Technologies
 The hot air heats the oven walls.
 These walls then radiate heat in all directions.
 Food in an oven then becomes cooked by both
convection and radiation.
 There is also conduction if a baking pan is used.
5.5 Heat Transfer and Technologies
 Did you know?
 Light-coloured surfaces reflect
more heat than dark surfaces.
 This is why people in hot
countries often wear lightcoloured clothing.
5.5 Heat Transfer and Technologies
 Getting Rid of the Heat
 Combustion of fuel inside an engine produces a large
quantity of thermal energy.
 If this energy were not removed, the engine would
overheat and be damaged.
 How is it protected?
5.5 Heat Transfer and Technologies
 The engine’s cooling system contains a liquid coolant
(most likely antifreeze).
 The coolant is pumped through the engine block to
the radiator. A radiator is a honeycomb made of a
metal alloy. The metal alloy is a good conductor. Heat
from the coolant is conducted through this alloy to air.
5.5 Heat Transfer and Technologies
 Either a fan or the motion of the vehicle forces this air
through the radiator. Heat is transferred to the air that
rushes through the radiator.
 These three techniques use conduction to protect
engines from heat damage.
5.5 Heat Transfer and Technologies
 Keeping it Cool
 When you put a little water on the back of your hand,
your hand becomes cool.
 That is because thermal energy transfers from your hand
to the water through conduction.
 Water absorbs heat from your hand and evaporates.
 Evaporation removes thermal energy as the water
molecules leave the water droplets and move into the air.
 Your hand feels cooler.
5.5 Heat Transfer and Technologies
 This form of cooling is usually called cooling by
evaporation.
 The evaporation caused the cooling, but the cooling
action started with conduction of heat away from your
hand.
5.5 Heat Transfer and Technologies
 Heat Transfer in a Refrigerator
 A. A fluid called a coolant circulates through the pipes.
 B. Heat from the food transfers to the cooler air surrounding
it. Thermal energy then transfers from the air to the coolant.
 C. The coolant evaporates as it gets warmer. It is pumped to
the compressor.
 D. When it reaches the compressor, pressure is applied to
change it back into a liquid.
 E. The liquid coolant is pumped to these coils. Thermal
energy is released into the room. The cycle starts again.
5.5 Heat Transfer and Technologies
 Air conditioners work in a similar manner. In this case, the
back of the unit is outside the room or house. To keep the
inside of the room cool, heat is dispersed to the outside air.
 Although useful, coolant technology has an environmental
cost. For the past 50 years, the liquid coolant used in
refrigerators and air conditioners has been liquid
chlorofluorocarbons, or CFCs. CFCs are responsible for
atmospheric ozone depletion. As of January 2000,
worldwide production of the most dangerous CFCs was to
be replaced by alternative liquid coolants. Research is
underway to produce environmentally safer but effective
coolants.
5.5 Heat Transfer and Technologies
 Practice!
 Check Your Understanding p. 101
REVIEW
 Chapter 5 Review p. 102 #s 1 – 12
 Heat Transfer Crossword
Chapter 6: Controlling Heat Transfer
Introduction
 Fire-walkers amaze tourists.
 They aim to convince their audiences that they have
some sort of special abilities.
 But! Fire-walkers have learned to reduce the transfer
of thermal energy from the red-hot coals to their feet.
 But how is this done?
Introduction
 *Hint: Cooks test to see if a skillet is hot enough by
dropping water into it.
 The pan is hot enough if the water drops dance across
the surface of the skillet.
Introduction
 We will re-visit the secrets of fire-walking later.
 We control heat transfer very day.
 Knowledge of differences in heat absorption is used in
many ways.
6.1 Absorbing and Losing Heat
 Recall from Chapter 5:
 Water moderates the temperature of the land around it.
 In this chapter we will discuss another reason why that
happens.
 Different materials absorb heat at different rates.
 This is referred to as heat absorption.
6.1 Absorbing and Losing Heat
 Specific Heat Capacity
 Different substances require different amounts of
thermal energy to raise their temperature the same
amount.
 This is true for all substances.
 Each substance requires a unique amount of heat gain or
loss to change its temperature.
6.1 Absorbing and Losing Heat
 Specific heat capacity – measures a substance’s ability
to absorb or lose heat
 Measured in joules per gram degrees Celsius
6.1 Absorbing and Losing Heat
 The specific heat capacity of a substance can change
depending on its state. For example, solid water (ice)
has a lower specific heat capacity than liquid water.
 This has to do in part with the relative attraction
between the molecules. Molecules that are close
together, as in a solid, have a stronger attraction to
each other. They require more energy to get moving.
 The joule is named after James Prescott Joule (1818–
1899), a brewer and physicist. It is represented by the
symbol J.
6.1 Absorbing and Losing Heat
 Example
 The specific heat capacity for water is
 What does this mean?


One gram of water absorbs 4.19 joules of heat to raise its
temperature 1°C
One gram of water loses 4.19 joules of heat to lower its
temperature 1°C
 Regardless of the amount of water, the amount of heat
needed to change the temperature does not change.
6.1 Absorbing and Losing Heat
 Another example:
 The specific heat capacity of sand is
 This means:
 To increase the temperature of 1 gram of sand by
1 °C would require 0.66 J of energy.
6.1 Absorbing and Losing Heat
 Consider:
 SHC of water =
 SHC of sand =
 Which has a higher specific heat capacity?
6.1 Absorbing and Losing Heat



Water!
This means that it takes more energy to
increase the temperature of water than it does
to increase the temperature of sand.
This is why sand on a sunny beach is much
warmer than the shallow water nearby.
6.1 Absorbing and Losing Heat
Substance
Specific Heat Capacity
Water
4.19
Motor oil
2.00
Vegetable oil
1.97
Air
0.995
glass
0.84
sand
0.66
Iron
0.45
copper
0.38
6.1 Absorbing and Losing Heat
 Warming Up and Cooling Down with Oceans
 Recall: oceans moderate shore areas
 Also, water has a high specific heat capacity.
 Oceans store more heat energy or thermal energy than
you might expect.
6.1 Absorbing and Losing Heat
 With water’s large SHC, water can absorb, store or
release much more thermal energy than land.
 That is another reason for land heating and cooling
quicker than lakes and oceans.
 SHC also affects climate in other ways:
 On a hot day, water will absorb heat. This slows down
the rise of temperature in the surrounding area.
 At night, water will release heat. This slows cooling in
the surrounding area.
6.1 Absorbing and Losing Heat
 The secrets of fire-walking
 Water has a very high specific heat capacity (4.184 kJ/K
kg), whereas coals have a very low one. Therefore the
foot's temperature tends to change less than the coal's.
 Water also has a high thermal conductivity, and on top
of that, the rich blood flow in the foot will carry away
the heat and spread it. On the other hand, coal has a
poor thermal conductivity, so the hotter body consists
only of the parts of the coal which is close to the foot.
6.1 Absorbing and Losing Heat
 When the coal cools down, its temperature sinks
below the flash point, so it stops burning, and no new
heat is generated.
 Firewalkers do not spend very much time on the coals,
and they keep moving.
 Calluses on the feet may offer an additional level of
protection, even if only from pain; however, most
people do not have calluses that would make any
significant difference.
6.1 Absorbing and Losing Heat
 Practice!
 Check Your Understanding p. 110
6.2 Keeping Heat at Home
 Recall: heat moves from hot toward cold.
 This happens especially in the winter.
 Heat often leaks through windows, doors, and roofs.
 Proper insulation can help this problem.
 Insulation slows heat transfer.
6.2 Keeping Heat at Home
 With energy costs rising, Canadians want to make sure
heat stays inside the house in winter.
 For Canadians, 50 to70 percent of energy costs go
toward heating or cooling our homes.
 If insulation is inadequate, much energy is wasted.
 This is bad for the environment and for the home
budget.
6.2 Keeping Heat at Home
 With insulation you get two benefits for the price of
one.
 The same insulation that keeps heat in during the
winter keeps heat out on a hot summer day.
 Knowledge of heat transfer teaches you how to keep
your home warm in the winter and cool in the
summer.
 But what makes a good insulator?
6.2 Keeping Heat at Home
 Insulation reduces heat transfer. A good insulator is
the opposite of a good conductor.
 With good insulation, the three forms of heat transfer
are slowed.
6.2 Keeping Heat at Home
 Heat convection and heat conduction can be
minimized in two ways:
 First, create a partial vacuum between the areas to be
insulated. This is done in vacuum bottles and in some
double-glazed windows with an inert gas between the
panes.
 Second, use trapped air. Still air provides 15 000 times
better insulation than metal.
6.2 Keeping Heat at Home
 Substances used for insulation are chosen for their low
thermal conductivity and their ability to trap air.
 Good conductors include cork, felt, cotton batting,
magnesium carbonate, and spun glass or fibreglass.
 Asbestos is an excellent insulator but it is a health
hazard and no longer used in construction.
6.2 Keeping Heat at Home
 Insulators work best when the air is dry. Moist air acts
as a much better heat conductor than dry air.
 To keep insulation dry, fibreglass is covered with
plastic sheeting before drywall is installed. Without
the plastic sheet, moisture from inside the house —
from cooking, bathing, and breathing — would
infiltrate the insulation and reduce its effectiveness.
 Radiant heat loss can be lessened by installing
aluminum foil, semi-reflective windows, and metal
roofing.
6.2 Keeping Heat at Home
 R-value
 Air transfers heat when it is moved by convection
currents.
 Air is an excellent insulator when it is held still.
 R-value is a measure of how well an insulating material
slows heat transfer.
 Materials with high R-values are better insulators than
those with low R-values.
i.e.) R-12 loses heat faster than one with R-16
6.2 Keeping Heat at Home
 When materials are used together, the total R-value is
the sum of the R-values of each material used.
 Example
 Walls in your home have 25 mm of expanded
polystyrene and 25 mm of rigid urethane foam. What is
the R-value of the insulation?
3.96 + 7.50 = R 11.46
Thickness of insulating material
Approximate R-Value
25 mm of air space in a wall cavity
2.04
25 mm of air space with reflective surface on inside
of wall cavity
5.54
25 mm of expanded polystyrene
3.96
25 mm of rigid urethane foam
7.50
25 mm of fibreglass
4.25
25 mm of solid wood
1.25
25 mm of wood shavings
2.42
25 mm of clay brick
0.11
25 mm of concrete
0.19
One thickness of glass
1.00
Thermal glass (2 thicknesses with air space)
1.80
6.2 Keeping Heat at Home
 Other Ways to Keep the Heat in Your House
 The empty space between the inside and outside wall of
a house is called a wall cavity.
 Filling the cavity with insulation stops convection
currents.
6.2 Keeping Heat at Home
 When insulation fills a wall cavity, there are many
pickets of trapped, still air.
 Foam pellets and poured insulation work in this way.
6.2 Keeping Heat at Home
 Windows and Doors That Keep Heat In
 Windows and doors are two weak points when you try to
keep a house warm.
 A single pane of glass is a poor insulator.
 Heat escapes quickly through glass.
 Leaks also develop around the panes and around the
edge of the windows.
6.2 Keeping Heat at Home
 Older houses use double windows and doors – called
storm windows and storm doors – to keep heat in.
 Today’s exterior doors and windows use double
glazing.
 This provides a space of still air.
 Insulation value of this still air in improved when air is
mixed with a gas such as argon.
6.2 Keeping Heat at Home
 Exterior doors used to be solid wood.
 Modern doors are cavities filled with insulation.
 Some are metal covered.
 To prevent heat transfer, there is a break in the metal
between the inside and outside.
6.2 Keeping Heat at Home
 Did You Know?
 Even the smallest crack (1.5 mm) around the outside of
one window, your furnace may burn an extra litre of fuel
per day!
6.2 Keeping Heat at Home
 Controlling Heat Transfer
 Pizza parlours keep pizza warm by transporting it in
insulated containers.
 As well as limiting heat transfer, the envelope must be
washable.
 This limitation prevents the use of some materials.
6.2 Keeping Heat at Home
 A vacuum bottle uses several of the same
technologies that keep your house warm in order to
keep food and beverages warm.
 Inside is a double glass jar. One jar is fitted inside the
other – similar to windows with a double pane.
 Some air is removed from between the two jars. That is
where the name comes from. The space between is a
partial vacuum.
6.2 Keeping Heat at Home
 Rubber or plastic keeps the glass away from the outer
case.
 The cap is insulated.
6.2 Keeping Heat at Home
 Kitchen and Workshop
 Large appliances (i.e. Stoves, refrigerators, freezers, even
dishwashers) are all insulated.
 Insulation slows heat transfer, keeping ovens hot and
freezers cold.
 What makes a good insulator?

Non-metals (i.e. Wood and plastic)
6.2 Keeping Heat at Home
 Examples:
 Plastic and/or wooden handles on kitchen utensils or
pots and pans
 Aprons and oven mitts
6.2 Keeping Heat at Home
 Practice!
 Check Your Understanding p. 119
6.2 Keeping Heat at Home
 Lab Prep p. 118
 When You’re Hot
 Challenge: Construct a container that will keep water
hot for an hour.
 Design Criteria:



Use any size container you want.
Use any insulation materials you want.
No thermoses, coolers, etc…
6.3 Keeping Yourself Warm
 The same techniques that keep our
houses warm, keeps our bodies warm.
 For example, on a cold day we may
choose to wear several layers.
 We choose inner layers for their open
weave and thickness.
 Air trapped in the material serves as
insulation.
 A windproof outer layer keeps warm air
from escaping.
6.3 Keeping Yourself Warm
 Clothing insulates by holding air between fibres.
 The better clothes trap air, the better insulators they
are.
 This is why thicker clothing tends to be warmer than
thinner.
 Thicker clothing reduces air flow and maintains still
air.
 Windproof material reduces or eliminates airflow
through the fibres.
6.3 Keeping Yourself Warm
 Some of the warmest winter clothing
contain down.
 Birds grow fluffy, down feathers.
 These feathers keep birds warm.
 Down is often quilted between the outer
shell and inner lining of a vest or jacket.
 When down is fluffed, it holds air in place.
 The jacket material keeps air from blowing
through the down and changing cold air for
warm.
6.3 Keeping Yourself Warm
 Recall: a dry body is a warm body.
 Vigorous activity causes sweat. Water causes cooling as
it evaporates.
 When working or playing outside, you want to protect
yourself from getting and staying damp.
 When you start to sweat, remove one layer, possibly
another.
 This allows heat to transfer out and your body to stay at
the right temperature.
 When you stop moving you can replace those layers.
6.3 Keeping Yourself Warm
 On a cold day, up to 40 percent of body heat is lost
through the head.
 Covering the head is important for heat retention.
 When a person becomes overheated in winter, a hat is
often the first piece of clothing removed to cool the
body and reduce perspiration.
6.3 Keeping Yourself Warm
 People of the North
 Inuit designed clothing is the
warmest.
 Traditionally, Caribou Inuit
clothes have two complete suits
on cold days.
 The inner set is worn with fur
next to the body.
 Body moisture is transferred
through the fur and through the
leather skin.
6.3 Keeping Yourself Warm
 Caribou fur is dense; individual hairs are hollow.
 Air trapped between and inside the hair provides
insulation.
 The outer parka is worn with the fur outside – this is
important for very cold days.
 The parka hood traps air in front of the wearer’s face.
 Frigid air is warmed before being breathed.
 This protects the wearer’s lungs.
6.3 Keeping Yourself Warm
 During extremely cold weather, water
vapour from the lungs can condense and
freeze on people’s faces and clothing.
 The hoods are designed to prevent
condensation.
 The edge of the hood, where ice might
form, is trimmed with fur.
 Ice does not stick to wolverine, wolf, or
some dog fur.
6.3 Keeping Yourself Warm
 Caribou and Copper Inuit wear up to four layers on
their feet in winter.
 Seal skin is preferred to boots because it is waterproof.
 Inuit parkas are much larger than we might expect.
 The large size allows wearers to bring their arms inside
this warm space.
6.3 Keeping Yourself Warm
 Did You Know?
 Some motorcyclists have clothing with built in
heaters!
 Heating elements are sewn into the clothing and warm
areas of the body such as the torso where a lot of heat
can be lost.
 The clothing runs off of a motorcycle battery and uses
less power than a headlight.
 The amount of heat can be controlled using a palmsized computer.
6.3 Keeping Yourself Warm
 Did You Know?
 People outside in winter protect themselves from
frostbite. Frostbite usually freezes hands, feet and the
face.
 One way to warm a cold hand is to tuck it into your
armpit for a few minutes!
6.3 Keeping Yourself Warm
 Keeping Cool
 Ever notice that people who live in
warmer climate areas where more
clothes?
 This is because they want to
minimize heat transfer.
 They wear long, thick robes to
protect the body from the Sun’s rays.
 These clothes are usually light in
colour to help reflect heat and to
allow body heat to escape.
6.3 Keeping Yourself Warm
 Oven mitts work in a similar manner.
 Their quilted material reduces heat transfer.
 Some include reflective material that also reduces heat
transfer.
6.3 Keeping Yourself Warm
 Dressing for Intense Heat – or Cold
 Firefighters and deep-sea divers have to deal with major
changes in temperature.
 But how?
6.3 Keeping Yourself Warm
 Firefighters’ suits are made of a
special material.
 Many contain flame retardant
chemicals.
 When flames or sparks come into
contact with the suit, the fabric
chars but does not burn.
 The charred material produces a
layer of insulation that protects the
firefighter from too much heat.
6.3 Keeping Yourself Warm
 Firefighters can suffer from heat stroke if




their body temperature increases too much.
Material on the inside of their fire suit
absorbs body moisture.
This helps to keep them cool.
Firefighters must monitor their own bodies.
If they get too hot, they could suffer from
heatstroke – even if it’s in the winter!
6.3 Keeping Yourself Warm
 The fabrics used in firefighters’ suits are tested to
determine their fire resistant qualities.
 They are tested by Scientists to see if they are safe
enough for firefighters to wear.
 This is done by dressing a mannequin in fire gear and
setting it on fire.
 These mannequins are equipped with sensors to
measure the rate and amount of heat transfer from the
fire.
6.3 Keeping Yourself Warm
 Even in hot climates, temperatures deep underwater




can be as cold as winter.
As a result, a diver’s suit should fit snugly.
Tight diving suits prevent cold water next to the skin
from causing cooling by conduction.
If cold ocean water moved in and out of the suit, a
diver would soon be cold.
Water could pick up heat from the diver’s body and
carry it off into the ocean.
6.3 Keeping Yourself Warm
 Dive suits are made of neoprene that has bubbles of
nitrogen trapped in the fabric.
 The more gas trapped in the fabric, the higher the
thermal value.
 These neoprene suits are well insulated to keep body
heat inside.
6.3 Keeping Yourself Warm
 Dive suits also have hoods for the
same reason that winter parkas have
hoods.
 Underwater, a great amount of heat
can be lost from a diver’s head.
 Some dive suits have titanium added
to the side of the fabric that is next
to the skin.
 The shiny titanium reflects heat
back into the body.
6.3 Keeping Yourself Warm
 Practice!
 Check Your Understanding p. 125