Lecture 29
pls-29.1
Temperature and Thermal Expansion
Media: (1)
Ring and ball bearing
(2)
Bimetallic strip
1.
Thermodynamics and Statistical Mechanics
Macroscopic Quantities
*Temperature
T
Free Energies
*—internal energy
U
—enthalpy
H
—Helmholtz energy
A
—Gibbs F.E.
G
Entropy
S
Pressure
P
*Heat
Q
Provides a microscopic basis for
the macroscopic thermodynamic
quantities
(Recall discussions of
ρ
and
P
)
2.
Internal Energy (U), Temperature (T), and Heat (Q)
Consider two identical
objects, except one is “hot” and one is “cold”
(Hot and cold refer to relative temperatures of the two objects.)
U
:
total
microscopic
energy
(
PE
KE
+
).
An extensive
quantity
Æ
scales
with the size of the object.
“hot”
“cold”

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Lecture 29
pls-29.2
For 2 identical objects, the hotter one has more internal energy
U
.
T
:
temperature
is related to
N
U
, where
N
= number of atoms or
molecules in object.
Generally, as
U
increases
T
increases.
Typical graph:
T
is an intensive
quantity
≡
ratio of 2 extensive quantities
Æ
T
is
independent
of the size of the object.

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