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====== Thermodynamic Analogies ======

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

====Lecture: PDM Dictionary (25 minutes)====

Consider a canonical thermodynamic system that consists of a gas in a cylinder with a moveable piston.  Help me draw a picture on the board.

SWBQ: On your small whiteboard, tell me a quantity you can measure for this system.

Students should generate the following.  For each, follow up with: How would you measure _____ for this system?  Then label them the picture, along with a way to measure that quantity:

  * Volume ($V$) - It can change if the piston moves and you can measure height with a ruler.
  * Temperature ($T$) - Put a thermometer in it!
  * Pressure ($p$) - If in equilibrium, $F_{net} = 0$, so if we account for the mass of the piston and the external pressure we can determine the pressure.  (What happens if there's disequilibrium?)

Follow-up: How would you hold each of these variables constant?

There is an analogy between the gas in a piston and the PDM.  With your group, discuss what is analogous between the two systems.

  : Good questions for helping students:
    * How do you change quantities in the gas?
    * How do you change quantities in the PDM?
    * How do you hold quantities constant?
    * Are there similarities in the dimensions of quantities between the two systems?

Final dictionary:
  * $p \rightarrow F_L$
  * $V \rightarrow x_L$
  * $T \rightarrow$ ? (students may not have enough information, but it should go to $F_R$.)

We are probably going to need a fourth variable here.  It turns out this fourth variable is Entropy ($S$), which you will learn about more during the rest of the course.  This is a good place to note that holding entropy constant is equivalent to insulating the system and remarking on how this is different from holding temperature constant.

  * [[..:..:activities:inact:in|???]] (SGA - 10 min) FIXME

  * New Surfaces activity - [[..:..:activities:eeact:eesurfstates|Thermodynamic States II]] (SGA - 10 min) FIXME

/*==== Homework for Energy and Entropy ==== NO HOMEWORK
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