# 5: Fundamentals of Thermodynamics


• 5.1: Temperature
In our study of classical mechanics, we learned that we had no choice but to lump lost mechanical energy into the microscopic random-motion realm that we broadly categorize as "thermal energy."  We will see here the rather remarkable result that this form of energy can be well quantified (under appropriate conditions) with a single measurable quantity called temperature.
• 5.2: Thermal Expansion
We can only measure temperature by the macroscopic effects caused by its change.  One of the most apparent effects is the expansion/contraction of solid and liquid matter when the temperature increases/decreases.
• 5.3: Heat Capacity and Phase Transitions
In classical mechanics, we saw that energy could be transferred from one system to another (or between objects within a system, or between kinetic and potential within a single object) through work.  Energy can also be transferred without work being done, as a result of a temperature difference.
• 5.4: Modes of Heat Transfer
Heat transfer always results from temperature differences, but there are three different modes of transfer, each with their own unique properties.
• 5.5: Thermodynamic States of Ideal Gases
There are several quantities that define the thermodynamic state of a system.  What these are, and how they relate to each other is best illustrated for the case of an ideal gas.
• 5.6: Equipartition of Energy
We know that temperature provides a measure of the thermal energy in a system, and that thermal energy is microscopic random mechanical energy.  We will see how the temperature change that results from an increase of thermal energy relates to the number of "modes" of microscopic mechanical energy are available.
• 5.7: Thermodynamic Processes
Thermodynamics deals with systems in equilibrium, but we can nevertheless discuss the progress of a system through various "adjacent" thermodynamic states.  This evolution through equilibrium states can take on many forms, each with their own unique properties.
• 5.8: Special Processes
There are an infinite number of ways for thermodynamic states to evolve, but there are only a few that we can easily implement by controlling the physical parameters of the system.

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