Brownian Ratchet

[A Tripolation]

I'm trying to figure out why the Brownian Ratchet fails as a violator of the second law of thermodynamics. The pages I've read do not make any sense to me. Can anyone explain it to me in somewhat simplistic terms? I'm only a few weeks into my Thermo class.

 

Thanks.

[timo]

EDIT: Seeing Mr. Skeptics post: I should probably have looked up the term "brownian ratchet" first . I was assuming you were talking about a switchable ratchet potential (like this one http://elmer.unibas.ch/bm/index.html) for some reason. You can probably ignore the rest of this post.

 

OLD POST:

I think you should try to formalize why they should be, first (and what the 2nd law of TD is - I'll assume the non-decrease of entropy in a closed system). So on first sight you'd think that it's a directed transport process so you take a ratchet potential over some bounded interval, put particles reacting to the potential in there at random positions, and then just wait for them to diffuse to one edge of the interval. In practice, you'll have to switch the potential on and off to achieve that. So the system is not closed, so a sorting of the particles is not excluded by that what I think you meant with the 2nd law (I really dislike giving numbers to concepts - who had this silly idea?!?).

 

So well: why do you think these ratchets would violate the 2nd law in the first place?

Edited September 23, 2010 by timo

[Mr Skeptic]

The brownian ratchet would only work if the ratchet were cold, otherwise the ratchet itself would wiggle too.

[A Tripolation]

The brownian ratchet would only work if the ratchet were cold, otherwise the ratchet itself would wiggle too.

 

And if the ratchet were cold enough to be at a lower temperature than the reservoir, then it would be utilizing temperature flow and thus be considered well under the domain of the second law?