temperature physics 313 professor lee carkner lecture 2
TRANSCRIPT
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Temperature
Physics 313Professor Lee
CarknerLecture 2
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Thermodynamics Thermodynamics is the study of energy
e.g. a cylinder of gas accelerated to high speed has an increased kinetic energy but the same temperature
We will discuss the properties of a system and how they relate to internal energy, through both the macroscopic and microscopic points of view
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Macroscopic Microscopic
Specify a few basic bulk properties
Classical Thermodynamics
Specify states of individual units
Statistical mechanics
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Systems Material separated from its
surroundings by a boundary
Closed
e.g. gas in a piston
Open
e.g. an automobile radiator
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Processes
State
Process
Quasi - Static (Quasi-Equilibrium) Process
slow changes Non-quasi static processes are discontinuous
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Equilibrium
Define two properties for a system
If the two properties remain constant the system is in equilibrium
A system is in equilibrium with itself if its properties are constant throughout the whole system
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System Boundaries
Adiabatic Wall
thermal insulator
Dithermal wall
thermal conductor
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Temperature Proxies Changes in temperature cause changes in other system
properties
Two consequences: We measure T by measuring changes in other properties
If T is not constant, nothing else is Often given at standard temperature (0 C) or room
temperature (20 C)
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Thermal Expansion The degree to which a linear distance
varies with temperature is given by:
Change in one dimension (linear expansion)
Very small (~one part in a million per
degree) in most cases
Note that itself is temperature dependant
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Typical “toothed” bridge expansion joint
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“Rocker” support that allows deck expansion
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“Sleeved” railing expansion section
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The Brooklyn Bridge
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The Brooklyn Bridge
Built: Designed: John A Roebling Chief Engineer: Washington A. Roebling Height: Length:
World’s longest suspension bridge until 1903 To learn more about the Brooklyn Bridge visit
your local library: The Great Bridge : The Epic Story of the
Building of the Brooklyn Bridge by David McCullough
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Brooklyn Bridge cables
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Stringing the Cables
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Main Cable
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Thermal Equilibrium
Two systems separated by a dithermal wall that do not change properties
If the two systems are not in thermal equilibrium they will exchange heat until they are
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Zeroth Law
Three systems A, B and T A and T -- B and T -- Then for A and B
Two systems in thermal equilibrium
with a third are in thermal equilibrium with each other
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Isotherms
Plot pressure and volume
Curve is called an isotherm
Temperature determines thermal equilibrium
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Temperature Take an object T and mark it so that
changes in its properties can be measured
Calibrate the measurements so that your scale corresponds to universally accepted situations
e.g. mercury thermometer
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Temperature Scales Gabriel Daniel Fahrenheit invented the mercury
thermometer in 1714
32 F is freezing point of water, 212 is chosen for boiling point (32+180)
Anders Celsius introduced his scale in 1742
William Thomson, Lord Kelvin, developed the absolute (Kelvin) scale from his analysis of ideal engines
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Temperatures
Universe (Planck time) ~ Universe (today) ~ Average star ~ Average dust cloud ~ Planet (Mercury) ~ Planet (Neptune) ~ Planet (habitable) ~