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

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Physics 213: Lecture 1, 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 1, 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 therm 0 Which stage never happens?
Physics 213: Lecture 1, 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 1, Pg 4 Act 1: Irreversibility Act 1: Irreversibility Do you really expect that the ice won’t melt and then evaporate? What won’t happen is for all the ice to jump up at one time . It will certainly all jump up, molecule-by-molecule . There are lots of slightly different ways for that to happen, compared to the number of ways of jumping up in a block. Our first hint that: which event will happen is set by the number of different ways that event could happen . 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
Physics 213: Lecture 1, Pg 5 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

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Physics 213: Lecture 1, Pg 6 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
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Lect04 - Lecture 4 Statistical Processes q q q q q Particle...

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