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====== Variables and Representations ======

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===== In-class Content =====

====Activity: PDM Variables====
[[..:..:activities:inact:inquantchange|Link to PDM Variables Activity]]

**Activity Highlights**
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==== Lecture: Contour Graphs of PDM Variables (25 minutes)=====

Fix $x_R$ and make a graph of $x_L$ vs. $F_L$.  (Don't let students be too precise.)

Repeat for 3 different fixed values of $x_R$ and graph them all on the same set of axes.  (Make sure students have explored enough of parameter space to see the nonlinearity.)

What variables is $x_L$ a function of?  (How do you indicate what you are holding constant on the graph?)

This is a contour graph!  You can write it using functional notation as $x_R(x_L,F_L)$.

Did we have to hold $x_R$ fixed?  What might we hold fixed instead?  

Try it again with fixed $F_R$!  (What variables is $x_L$ a function of now?)

Wrap-up: this is a good opportunity to discuss the different kinds of representations we use in thermodynamics, such as experiments, tables, graphs, and symbols.  This can be open-ended and student generated, but a good conclusion is that in each case we want to represent certain information like which variables depend on which other variables and which things are being held constant.

====Activity: Thermodynamic States I====
[[..:..:activities:eeact:eesurfstates|Link to Thermodynamic States I Activity]]

**Activity Highlights**
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==== Homework ====
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