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) ~