Temperature

Temperature
A convenient operational definition of temperature is that it is a measure
of the average translational kinetic energy associated with the disordered
microscopic motion of atoms and molecules. The flow of heat is from a
high temperature region toward a lower temperature region. The details of
the relationship to molecular motion are described in kinetic theory.The
temperature defined from kinetic theory is called the kinetic temperature.
Temperature is not directly proportional to internal energy since
temperature measures only the kinetic energy part of the internal energy,
so two objects with the same temperature do not in general have the same
internal energy (see water-metal example). Temperatures are measured in
one of the three standard temperature scales (Celsius, Kelvin, and
Fahrenheit).


More generalized view of temperature

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Temperature
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Temperature Scales
The Celsius, Kelvin, and Fahrenheit temperature scales are shown in
relation to the phase change temperatures of water. The Kelvin scale is
called absolute temperature and the Kelvin is the SI unit for temperature.







The triple point of water is 273.16 K, and that is an international standard
temperature point. The freezing point of water at one atmosphere pressure,
0.00°C, is 0.01K below that at 273.15 K. If you want to be really precise
about it, the boiling point is 373.125 K, or 99.975 °C relative to the
standard pressure freezing point. But for general purposes, just 0 °C and
100 °C are precise enough.
Standard temperature points

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Temperature
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Internal
energy
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Temperature Standard Points
While the typical treatment of temperature scales takes the freezing point
of water to be 0C and the boiling point at standard pressure to be 100C,
there are more precise treatments of standard points for defining
temperatures. By international agreement, one standard point is the triple
point of water which has been defined to be 273.16K. The freezing point
of water at atmospheric pressure is .01K below this at 273.15K.
In order to obtain a second standard point by means of a thermometer
which doesn't depend on the particular substance used to make it, a
constant-volume gas thermometer was chosen to measure the boiling point
of water. This method is based upon the ideal gas law, i.e., the assumption
that if the volume is fixed, the temperature is directly proportional to the
pressure. This measurement leads to a boiling point of 373.125K or 99.975
C above freezing at standard pressure. This measurement is independent
of the gas used to make the thermometer. Ordinary gases do not behave
exactly as ideal gases and are better described by the van der
Waals equation of state, but as they are extrapolated to zero pressure, they
all project to the same value for the zero of the Kelvin scale.
Table of standard temperature points

Index

Temperature
concepts

Internal
energy
concepts

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