SAC.LONG%USC-ISIE@sri-unix.UUCP (01/15/84)
Personally, I am not a Physicist by trade, though I encounter and have encountered such matters involving something to do with the filed (no pun intended) in my work. It is my understanding that science is consistent and organized, so-to-speak. Then could someone who is a physicist please explain to one who is not why it is so difficult to explain why soda freezes when opened after being cold for a long time. I am not concerned about the soda freezing, but more-so why it is so difficult to explain the phenomenon consistently among the community of Physicists. I am very sincere in asking this question, so those of you who wish to be sarcastic, please direct your comments either to me directly (sac.long at usc-isie) or say nothing. Thank you. -- Steve
gwyn%brl-vld@sri-unix.UUCP (01/15/84)
From: Doug Gwyn (VLD/VMB) <gwyn@brl-vld> One problem is that the idealized "physics" taught in school tends to dwell on phenomena that can be modeled with simple mathematics. Phase transitions do not fall into this category. I don't think there is any real mystery about the freezing of a supercooled solution being triggered by sudden release of pressure, but great care must be taken in correctly applying thermodynamics to the situation, since principles that are derived from consideration of slow, reversible change simply do not apply in this case. Non- equilibrium thermodynamics should be able to give an unambiguous statement of what happens, although I don't find the problem of enough interest to go to the trouble of working it out. As to the possibility of several "equally correct" answers, that is a consequence of the multiplicity of chains of reasoning that can lead to the same result. What one considers a good "explanation" also enters into the debate over the best answer. Finally, Sturgeon's law applies: 90% of EVERYthing is crap, and that applies to the work of scientists too. After the recent creationism noise on this mailing list, it should be apparent that nobody is filtering the contributions to eliminate bogus responses (nor am I suggesting that they should).
peters@cubsvax.UUCP (01/16/84)
You ask why it isn't simple to answer the question why a bottle
of very cold Coke freezes when it's opened.
You raise an interesting point... and in doing so exemplify one of the
common misconceptions about not just physics but science in general:
namely, that simple-sounding "problems" out there in the real world are
simple to solve, and that all scientsts will agree on a solution. It
ain't that way.
First of all, there are only about a dozen people in the world who know
exactly what is in Coca Cola, and they aren't telling. So, since
everything we add to water changes its properties, we have to come up
with a good guess about what Coke is -- or at least a guess which, though
it may not taste like Coke, has enough in it to explain the properties we
observe. This we call a "model." I used water in my analysis, though
I also pointed out that the dissolved sugar will increase the viscosity
at low temperatures, thereby leading to supercooling. I used water
because it's easy to look up things like solubility of CO2 in water,
and hard to find solubility of CO2 in a solution of sucrose in water
at a specific concentration.
And so it goes. See also net.misc (I believe) for a current discussion
about how mpg relates to mph in driving. Or net.audio for a current
discussion about whether digital recording is better/worse/no different
than analog recording, or whether CD's are better/worse/no different than
vinyl discs. In all these discussions people are putting forth *models*
of the phenomena under discussion, and doing calculations, sometimes
involved ones, to explain why they think their point of view is correct.
Occasionally someone disputes a calculation, but usually the discussion
is about either (a) new data -- that is, someone *observes* a phenomenon
which s/he thinks is relevant, and which s/he feels has been overlooked --
or else (b) whether the model used a basis for calculation really
includes all the essential aspects of the *physical system* under
discussion.
Systems which can really be modelled in their entirety exist very
few places outside a laboratory; experimental science is the art
of devising such systems, and scientists try to devise experiments
for which (a) they know exactly what the result will mean, and (b)
it means something which people care about. That's tough, and
that's why science is hard.
{philabs,cmcl2!rocky2}!cubsvax!peters
(Peter S Shenkin; Dept of Biol Sci; Columbia Univ; NY, NY 10027; 212-280-5517)flinn@seismo.UUCP (E. A. Flinn) (01/17/84)
Since miles per gallons has dimensions length^(-2), it can be expressed in, for example, reciprocal acres.