Today’s Topics:
• Temperature
• Thermal expansion
• Heat
• Specific heat
Temperature
• Microscopic: measure of mean ___________________ of molecules
of a gas
Study of thermodynamics
thermos – ________
dynamis – ________
• Macroscopic: measure of thermal _________________
 _________ Law of Thermodynamics – Two systems are in
thermal equilibrium if and only if they have the same
temperature.
Thermodynamics: study of the
effects of work, heat, and
energy on a system.
• Thermal ______________: particular object or set of objects;
interested in temperature dependent properties; everything else is
called the environment.
• Thermal ______________: temperature and temperature
dependent properties no longer changing.
• Thermal ______________: thermal system so large it maintains a
constant temperature when it interacts with other thermal systems;
also called a heat bath.
EF 152 2016 Lecture 3-1
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Scale
Units
Water
Freezing
Point
Water
Boiling
Point
Fahrenheit
°F
32°F
212°F
Celsius
°C
0°C
100°C
Kelvin
Kelvin
273 K
373 K
T
Rankine
°R
491.6°R
671.6°R
T
EF 152 2016 Lecture 3-1
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Thermal Expansion
Thermal Stresses
Solids: change in length is, to a good approximation, __________
proportional to change in temperature.
If expansion or contraction is restrained, stresses will develop. These are
called ________________
l 
α: coefficient of thermal expansion
l0: original length
Material
(/°C)
Aluminum
25x10-6
Brass
19x10-6
Gold
14x10-6
Iron or Steel
12x10-6
Glass (ordinary)
9x10-6
Glass (Pyrex®)
3x10-6
A 128 ft long Neyland Stadium
column shortens about 0.1 inch
under the spectator load. How
much does the column lengthen
as the temperature goes from
50°F to 75°F?
7.3 10 /
Thermal expansion: ∆
∆
∆
A welded steel rail is laid at 55°F.
What is the thermal stress in the
rail on a hot summer day when
the rail temperature is 120°F?
= 7.3x10-6 /°F, E = 29x106 lb/in2
E: modulus of elasticity
Why do
pipelines
zigzag?
What would a negative coefficient
of thermal expansion indicate?
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Volume Expansion
Heat
_______: Symbol commonly used for heat.
Coefficient of Volume Expansion, β: fractional change of volume due to a
unit temperature change.
V  V0 T
For a solid,
Material
_____________: measuring heat
_________: amount of heat necessary to raise 1 gram of water 1°C
The 15 gallon steel gas tank of a
car is filled to the top with
gasoline at 20°C (68°F). The car
sits in the sun and the tank and
gas reach a temperature of 38°C
(100.4°F). How much gasoline
overflows from the tank? βgas =
950x10-6/°C, βsteel = 36x10-6/°C
3
β(/°C)
____________ or _________: amount of heat
necessary to raise 1 kilogram of water 1°C
_________________________: amount of heat
1 BTU = 252.02 cal
= 0.252 Cal
necessary to raise 1 lb of water 1°F
Aluminum
75x10-6
Brass
56x10-6
Gold
42x10-6
Iron or Steel
36x10-6

_______________: objects in contact
Gasoline
950x10-6
Mercury
180x10-6

_______________: fluid (liquid or gas) between objects
Water
210x10-6

_______________: electromagnetic waves
Mechanisms of heat transfer
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Mechanical Equivalent of Heat
Heat Capacity
• Experiment by James Prescott Joule,
an English brewer in 1800s
Amount of heat required to change the
temperature is proportional to ______
and ____
• Falling weight turned a paddle
Q  mcT
• Joule determined that there
is a precise equivalent of
work done on a system
and the heat flow into it
c (cal/g-°C)
Aluminum
0.22
Glass
0.20
Iron or Steel
0.11
Water
Example: Cup of Coffee
• 4.186 J = 1 cal
200 cm3 of French Vanilla coffee at 95°C is poured into a
150 g glass cup initially at 25°C. Assuming no heat flows
to the surroundings, what is the common temperature?
Conservation of Energy
EF 151
c = specific heat
Material
a.) Teq > 60°C
b.) Teq = 60°C
Thermo
c.) Teq < 60°C
State Variables
Rework with 400 cal of heat were lost to the surroundings
Changes to System
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