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Fun With Thermodynamics

By drorzel on August 2, 2006.

Temperatures in Schenectady hit the mid-90's yesterday (do your own metric conversions), so I took the opportunity to do a little experimental thermodynamics: I played pick-up soccer after work with some of the students who are here for the summer. On the field-turf football field, which was a good ten degrees hotter than the ambient temperature elsewhere. It was an excellent opportunity to run down Jim's checklist of heat stress symptoms ("Hmmm... I'm not sweating as much as I was a little while ago. Perhaps this would be a good time to go sit in the shade and drink water...").

(Let this be a lesson about the signficiance of a Ph.D.: Even people with advanced degrees in hard sciences can do very, very stupid things for the sake of amusement. Adding injury to insult, I busted up my toe kicking the Director of Residence Life in the ankle (I was trying for the ball), so I'm hobbling today.)

On the more general subject of thermodynamics, let me take this opportunity to plug Sean Carroll's really excellent post about entropy and the arrow of time. The comment thread has some great stuff as well.

It's going to be hot again today, but this time, I think I'll stay in my nice, air-conditioned office, and work on my tenure packet...

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Physics

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By Mark Paris (not verified) on 02 Aug 2006 #permalink

Entropy is a demonstrably weak arrow of time,

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http://mit.edu/chemistry/deutch/technical/pdf14/146JOC63p3821(1998).pdf

Angular momentum is a strong arrow of time. Consider a hollow right cylinder with one port normal to its base and another port tangent to its side with its pipe at right angles to that of the base inlet. Pump water base entry and tangential exit - no problem. Reverse time to pump water tangential entry and base exit - no flow. It's a fluid diode with no internal restrictions because angular momentum is conserved. As with an electrical diode, it has a threshold value.