Physics 150 Fall 2003
Lect. 7. The second law of thermodynamics
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Summary
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The first law states that energy always remains the same
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The second law states that entropy (disorder) always increases!
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Sets a "direction of time"
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Irreversible phenomena
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Important in philosophical arguments
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The universe in running down
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"Thermal death"
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How is progress and evolution possible?
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Basic understanding in terms of probability
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An isolated system always evolves to a state of great probability
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Because ordinary objects are made up of extremely large numbers of atoms,
the probabilities are astronomically large (even larger) that nature evolves in the direction
required by the second law
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Practical consequences
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Heat engines
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Maximum possible efficiency is that of a reversible engine
Next Time: Electric and magnetic forces
Read for Next Time: March, Ch. 6