There's a good companion article in the NFFS 2003 Sympo by Fred Pearce
which discusses temperature effects on rubber polymers and energy in laymans
terms.
Rick Pangell
Editor of "The Max-Out" Newsletter of
The Magnificent Mountain Men FF Club of Colorado
In a message dated 6/23/2010 3:53:32 A.M. Mountain Daylight Time,
bensaks_at_gmail.com writes:
Found this on wikipedia and I thought it might be interesting to discuss
how our winding and flying(unwinding) affect the rubber. The physics is a
little heavy.
Thermodynamics
Temperature affects the elasticity of a rubber band in an unusual way.
Heating causes the rubber band to contract, and cooling causes expansion._[9]_
(
http://en.wikipedia.org/wiki/Rubber_band#cite_note-8)
An interesting effect of rubber bands in _thermodynamics_
(
http://en.wikipedia.org/wiki/Thermodynamic) is that stretching a rubber band will produce
heat (press it against your lips), while stretching it and then releasing
it will produce an _endothermic_ (
http://en.wikipedia.org/wiki/Endothermic)
reaction, causing it to become cooler. This phenomenon can be explained
with _Gibb's Free Energy_ (
http://en.wikipedia.org/wiki/Gibb's_Free_Energy) .
Rearranging ÄG=ÄH-TÄS, where G is the free energy, H is the _enthalpy_
(
http://en.wikipedia.org/wiki/Enthalpy) , and S is the _entropy_
(
http://en.wikipedia.org/wiki/Entropy) , we get TÄS=ÄH-ÄG. Since stretching is
nonspontaneous, as it requires an external heat, TÄS must be negative. Since T is
always positive (it can never reach _absolute zero_
(
http://en.wikipedia.org/wiki/Absolute_zero) ), the ÄS must be negative, inferring that the rubber in
its natural state is more entangled (fewer _microstates_
(
http://en.wikipedia.org/wiki/Microstate_(statistical_mechanics)) ) than when it is under
tension. Thus, when the tension is removed, the reaction is spontaneous, leading
ÄG to be negative. Consequently, the cooling effect must result in a
positive _ÄG_ (
http://en.wikipedia.org/wiki/Gibb's_Free_Energy) , so ÄS will be
positive there._[10]_ (
http://en.wikipedia.org/wiki/Rubber_band#cite_note-9)
_[11]_ (
http://en.wikipedia.org/wiki/Rubber_band#cite_note-10)
--
BEN SAKS
_www.bensaks.carbonmade.com_ (http://www.bensaks.carbonmade.com/)
Received on Wed Jun 23 2010 - 07:12:33 CEST