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Lecture 33 - Lecture 33 pls-33.1 Diffusion Media 1 Hot/cold...

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Lecture 33 pls-33.1 Diffusion Media: 1. Hot/cold diffusion demo Clicker questions 1 – 3 1. Ballistic Motion As was discussed in the last lecture, the root-mean-square (rms) velocity is defined as m T k v v B rms 3 2 = . When thinking about thermal motion, one often uses rms v for the average speed, although it is technically the square root of the average of the velocity squared. Clicker questions 4 and 5 Example : N 2 molecule at RT: × × = kg 66 . 1 28 K 300 ) K J 10 38 . 1 ( 3 27 23 rms v 500 m/s Æ if N 2 molecules moved ballistically (i.e., without hitting other air molecules) they would travel 500 m in 1 s Æ Would take < 0.1 s to cross the lecture hall. However, the average molecular spacing between air molecules is ~ 3 nm , so any given molecule doesn’t travel very far until it hits another molecule. This must be taken into account if one is interested in the average motion of a given molecule.
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Lecture 33 pls-33.2 2. Microscopic Random Walk random walk model The random walk model
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