Re: [Phys-l] teaching energy

[Brian Whatcott <betwys1@sbcglobal.net>]

At 10:50 AM 9/29/2006, BC, you wrote:
>  "The analogy to the rubber band is a visual example:  The band
> changes its geometry as you stretch it, and energy resides in that altered
> geometry.  Allowing the band to return to its "natural" geometry releases
> the energy."
>
> Not a good example except in the "mind's eye"
>
> Try this experiment:
>
> W/ a high quality very large rubber band Stretch it and hold 'til
> equilibrium.  Then using your lips as a thermometer (hold gently against one)
> allow the band to relax.  If you are releasing it's energy it should warm,
> right?  What does happen?
>
> Rubber makes rather interesting thermodynamic engines

An aside:
Fabric reinforced belts are used to transfer motion to water pump,
 alternator, power steering pump etc.,  in the automobile.
The curious property to which BC alludes, that these belts tend to
 shrink when heated is unfortunate, in the context of the fixed
tensioning methods formerly employed for cars.
  So it is a very encouraging thing to see that current American
 vehicles are adopting sprung tensioning pulleys.



Brian Whatcott    Altus OK    Eureka!