Energy stored in a mechanical watch spring

[jasc15]

My mind often wanders while driving, and since I had been reading a lot about watches one particular day, as well as having read an article on springs made of carbon nano-tubes, I thought it might be possible to power small electronic devices with a mechanical self-winding watch movement. However, I had a hard time estimating the stored energy in a watch mainspring. So with some of the practical considerations aside, how would I go about estimating this? or better yet, where could I find out.

 

[jasc15]

While trying to find an answer, I came across this interesting problem:

What happens to the potential energy of a wound watch spring when it is dissolved in acid?

This problem was asked in a 1901 issue of the NY Times. http://query.nytimes.com/mem/archive-free/pdf?res=9B00E1D81330E132A25754C1A9659C946097D6CF

 

[FlexGunship]

While trying to find an answer, I came across this interesting problem:



This problem was asked in a 1901 issue of the NY Times. http://query.nytimes.com/mem/archive-free/pdf?res=9B00E1D81330E132A25754C1A9659C946097D6CF

At some point prior to the total degradation of the spring, it would fracture at a single location thus releasing the potential energy and probably splashing acid everywhere.

DO NOT RECOMMEND TRYING.

 

[Phrak]

No, the energy is released slowly into the acid with each layer of spring removed. The effect is to heat the acid. If the spring is the common helical variety, each layer is in shear, tensioned and compressed in the +/- 45 degree directions along the surface. If the diameter is eroded to half, the large majority of the potential energy is removed. 15/16th, is it?

Not a lot of potential energy is left, as it loses diameter, to cause a sudden failure at some point along its length. The last bit dissolves in a whimper, not a bang.