Sunday, September 21, 2008

Wild Encounters I: Snakes of Tallahassee

After seven years in Ann Arbor, Michigan, one gets used to skunks, racoons, deer and the like. So when we moved to Tallahassee, a couple of years ago, and people told us that there is a lot of wildlife there, we weren't particularly alarmed. There is a certain glamor in living in wild parts.

A key difference between Tallahassee and Ann Arbor is the relative numbers in which the insect and reptile kingdoms are represented. The insects actually bother me more, because more insects means more lizards and frogs, and this entire ecosystem wants to sublet your house without paying rent.

I like to run, and prefer running outdoors, generally on trails. Tallahassee is great because, you can run year round unless the heavens are leaking or a Hurricane stops by to say hello. What amazes me however is the amount of "wild" stuff you encounter. On two occasions (in spring) I've had snakes lazily stretching out on the trail, perhaps hoping somebody will give them a massage or something. A couple of other times we've seen snakes in close to the edge of water bodies. Since we like camping and running in the woods, I decided to do a little researching and am presenting part I here. Part I, is all about the "water moccasin" which sounds like comfy shoe you'd wear to the beach, but in reality is a poisonous reptile with a reputation for meanness.

I started my research at the fountain of all knowledge.


I found the picture below here (by Andy Wraithmell). A water moccasin is also called a cottonmouth (another soft name, these herpetologists need to get real!) because when it opens its mouth (as a defensive power play) all you see is white like cotton.

However, it belongs to the viper family (I've also learned that rattlesnakes are pit-vipers not found in the Old World.) Cottonmouths are found all over Florida, so I have to run really far to get away from their territory. From an hour long of googling it seems to me that the degree of their aggressiveness seems to vary. Anecdotal blogs, opinions seem to reiterate that these snakes are highly aggressive, while others trying to back up these characteristics with quantitative studies seem to suggest otherwise. But I guess one shouldn't take chances. Which means one has to be able to tell a water moccasin when one sees it.

Things to look for.

1. about 3 feet long
2. in water swims with most of its body above/on water surface
3. head cocked at 45 degrees (see pic above)
4. near water (likes to laze around branches etc.)
5. if mouth open, you see lots of "cotton"
6. like all vipers has a well defined triangular head.

Sunday, September 14, 2008

Everyday Thermodynamics I: Why does warm air rise?

A new Fall semester started at Florida State University. In other parts of the world, a riot of colors slowly descends with
beauty, grace and briskness. The air has a newfound cold bite, and is filled with the anticipation of Saturdays and college football. Not so, in Tallahassee.

In Tallahassee, we sweat.

And for the first 10 days in the Engineering Building we steamed as the AC broke yet again. And I noticed something interesting. It is funny, how what we notice depends on what we think. I am teaching thermodynamics for the third straight year (which is great in terms of the time such a luxury affords me), and I noticed right away that my office which is on the third floor was much warmer than the ground floor although the air-conditioning for the entire building had failed.

What had happened was obvious. "Warm air rises, cold air sinks!". Unfortunately for the kids taking ECH 3101, I have this section called "bonus surprise tests" (whose popularity is variable, but usually negative) and I decided that this was, what people who sound like experts call a "teaching moment". Pronto, I put this on their first surprise test, and asked them to explain why warm air rises, assuming that air is an ideal gas (which in this case is not a bad approximation)!

The answer is fairly trivial. To aid thinking it is useful to ask why water sinks and oil rises. It is immediately clear that the quantity to go after is density. The rest, however important, is ironing out the details.

The ideal gas law says PV=NRT, where symbols have their usual meaning. Therefore, N/V=P/RT. N/V is the molar density. The pressure doesn't change too much over 20 m (air pressure drops with altitude, by about 0.01 bar per 100 m.). Therefore density is inversely proportional to temperature. Thus cold air is more dense. QED.

The same effect, of-course, underlies the rising of hot air balloons like the one pictured left.

Just to dispel any lingering suspicion that you may have figured everything out here is an interesting question as an epilogue. If warm air rises, why is it cold in the mountains? Think about it for a while and then click here (pdf) for the answer.