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# Lect04 - Lecture 4 Statistical Processes q q q q q Particle...

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Physics 213: Lecture 4, Pg 1 Particle Diffusion Particle Diffusion Counting and Probability Counting and Probability The meaning of equilibrium The meaning of equilibrium Two-cell box and the concept of “microstates” Two-cell box and the concept of “microstates” Other binomial systems: coin flip, spins Other binomial systems: coin flip, spins Statistical Processes Statistical Processes Lecture 4 Reference for Lecture 4: Elements Ch 5 Reference for Lecture 5: Elements Ch 6 http://intro.chem.okstate.edu/1314F00/Laboratory/GLP.htm

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Physics 213: Lecture 4, Pg 2 v v = 0 End with v = 0 mgh = U therm ½ mv 2 = U therm Thermal energy in block converted to c.o.m. KE Thermal energy Kinetic energy Potential energy Have you ever seen this happen? (when you weren’t asleep or on medication) h = U therm /mg U ther m 0 Which stage never happens?
Physics 213: Lecture 4, Pg 3 Replace the block in the last problem with an ice cube of the same weight. Will that stuff jump off the table? a. Yes b. No Act 1: Irreversibility Act 1: Irreversibility

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Physics 213: Lecture 4, Pg 4 The direction of time The direction of time In Physics 211 (Classical Mechanics), most of the processes you learned about were reversible . For example, watch a movie of a pendulum swinging or a ball rolling down a plane. Can you tell from the action whether the movie is being played forwards or backwards? The real world is full of irreversible processes. E.g., a block sliding across a rough surface or a rocket being launched. You know whether a movie of those is being played backwards or forwards. Time has a direction . Consider the free expansion of a gas (movie). On a microscopic scale motion is reversible , so …. ... How can you in general know which way is forward? Our answer will be that total entropy never decreases. Which of the following are irreversible processes? Α basketball bouncing on the floor An object sliding down a plane A balloon popping Rusting, e.g., Fe + O 2 Fe 2 O 3
Physics 213: Lecture 4, Pg 5 Brownian Motion Brownian Motion 1828 Robert Brown (English botanist) noticed that pollen seeds in still water exhibited an incessant, irregular “swarming” motion. There were several suggestion explanations, but none really worked until… 1905: Einstein, assuming the random motion of as- yet-unobserved molecules making up the water, was able to precisely explain the motion of the pollen --- as a diffusive random walk. Einstein’s concrete predictions (he suggested measuring the mean-square displacements of the particles) led Jean Perrin to experiments confirming kinetic theory and the existence of atoms!

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Physics 213: Lecture 4, Pg 6 Random Walk Problem: Diffusion of molecules Random Walk Problem: Diffusion of molecules Picture can also apply to: impurity atoms in an electronic device defects in a crystal sound waves carrying heat in solid!
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Lect04 - Lecture 4 Statistical Processes q q q q q Particle...

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