Part III: Heat
Chapter 21
Temperature, Heat &
Thermal Expansion
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Temperature
Temperature of an
object indicates
average internal
energy (due to
molecular motion)
of the object.
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Temperature Scales
Heat Transfer
Heat always flows from
high temperature
objects to low
temperature objects.
Heat flow stops when
temperatures equal.
Various ways by which
heat may flow.
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Physics 1 (Garcia) SJSU
Heat flows from
child into air
75º
98º
32º
Heat flows from
child and air into
the ice cream
Temperature Conversions
To convert between Celsius and Fahrenheit
temperatures, use the following equation
• F=9/5C + 32
• C=(F-32)*5/9
To Convert between Celsius and Kelvin
temperatures, use the following
K=C+273
C=K-273
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Total versus Average
The total amount of money in this
room is probably around $1000.
The average amount of money per
person is probably around $20.
Temperature of an object depends
on the average amount of energy
per molecule, not the total.
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Bucket of warm water can
have more internal energy
Physics
1 (Garcia)
than
cup ofSJSU
hot water.
80 °F
100 °F
Internal Energy
Internal energy of an
object depends on:
• Temperature
• Mass
• Material
Water
1 kg
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Temperature
Internal
Energy
300 K
120,000 J
1 kg
200 K
80,000 J
1000
grams
100 K
40,000 J
0K
0 Joules
Temperature
Internal
Energy
300 K
120 J
200 K
80 J
Iron
Temperature
Internal
Energy
300 K
1,200,000 J
200 K
800,000 J
100 K
400,000 J
100 K
40 J
0K
0 JoulesPhysics 1 (Garcia) SJSU
0K
0 Joules
Iron
1 gram
Money and Happiness
Some people need a lot of
money to make them
happy. Some don’t.
Some materials, such as
water, need a lot of
energy to raise their
temperature.
Some materials, such as
iron, need little energy to
raise their temperature.
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Physics 1 (Garcia) SJSU
Nicole Richie &
Paris Hilton
MAHATMA GANDHI
Increasing Internal Energy
Can increase internal energy (and
temperature) by tapping energy sources.
Chemical energy
released in fire
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Electric energy
heats burner
Work and Heat
May increase internal energy by exerting a
force to do mechanical work.
Rub hands together
for warmth
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Strike an iron surface with
great force and red-hot
sparks are created
Specific Heat Capacity
Specific heat
capacity is the
internal energy
required to raise
one gram of a
material by one
degree of
temperature.
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Filling and crust at same
temperature yet mouth
burned only by the filling.
Filling has high specific heat capacity
Crust has low specific heat capacity
Physics 1 (Garcia) SJSU
Check Yourself
Why does a piece of watermelon stay cool for a
longer time than sandwiches do when both are
removed from a cooler on a hot day?
Why is it that the climate in the desert is so hot
during the day yet so cold at night?
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Demo: Boil Water in Paper Cup
Because of high heat
capacity of water, the
large amount of heat
added by the flame
raises the temperature
of the water until boiling.
If the cup is filled with
sand instead of water
then it burns quickly.
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Cup with
sand
Cup with
water
Thermal Expansion
Due to increased molecular motion, most
materials expand as temperature increases.
Space allows
for expansion
Sidewalk buckles and cracks due to
expansion on a hot summer day
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Thermal Expansion
• Water is an exception.
– Water contracts as it cools down to 4 degrees
Celsius, then expands as it cools down to 0
degrees Celsius.
• This is how pot holes form, soda bottles explode
when left in the freezer, and ice cubes float
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Demo: Expansion of a Ring
Metal ball barely fits past the
metal ring.
Not surprising that heated ball
won’t pass through cold ring.
Will cold ball pass through
heated (expanded) ring?
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Demo: Bi-metallic Strip
Different materials
have different rates
of expansion.
Brass
Brass expands
more than steel
when heated
Thermostat
HOT
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COLD
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Bi-metallic
Spiral strip
Temperature Conversions
• To convert Celsius to Kelvin
K=C + 273
• To convert Celsius to Fahrenheit
9
F= C  32
5
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