2: Thermodynamics Review
1. Objects are at equilibrium with each other only when they have the same "degree of hotness" :concept of Temperature:
2. The impossibility of perpetual motion machines :concept of Internal Energy.
3. The impossibility of reversing any natural process in its entirety : concept of Entropy
Closed System: A collection of matter of fixed identity. The boundaries may change, but there can be no mass transfer across them. Example: a nuclear submarine moving under the sea.
Control Volume: A region of fixed shape, location, and volume. Matter can enter and leave the boundaries. Example: the inside of a classroom, or a jet engine.
Note: The laws of thermodynamics are usually found written for closed systems. However, jet engines are more easily modeled as control volumes, since we don't usually care which particular molecules of air are inside the engine at any given time.