Download - Temperature
Temperature
Physics 313Professor Lee
CarknerLecture 2
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
Macroscopic Microscopic
Specify a few basic bulk properties
Classical Thermodynamics
Specify states of individual units
Statistical mechanics
Systems Material separated from its
surroundings by a boundary
Closed
e.g. gas in a piston Open
e.g. an automobile radiator
Processes State
Process
Quasi - Static (Quasi-Equilibrium) Process
slow changes Non-quasi static processes are discontinuous
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
System Boundaries Adiabatic Wall
thermal insulator Dithermal wall
thermal conductor
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)
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
Typical “toothed” bridge expansion joint
“Rocker” support that allows deck expansion
“Sleeved” railing expansion section
The Brooklyn Bridge
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
Brooklyn Bridge cables
Stringing the Cables
Main Cable
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
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
Isotherms Plot pressure and volume
Curve is called an isotherm
Temperature determines thermal equilibrium
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
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
Temperatures Universe (Planck time) ~ Universe (today) ~ Average star ~ Average dust cloud ~ Planet (Mercury) ~ Planet (Neptune) ~ Planet (habitable) ~