Transcript A Brief History of Planetary Science

Temperature
Physics 313
Professor Lee Carkner
Lecture 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

Specify states of
individual units

Classical
Thermodynamics
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 a 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) ~