Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Energy stored in a mechanical watch spring

  1. May 19, 2010 #1
    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.
  2. jcsd
  3. May 20, 2010 #2
    While trying to find an answer, I came across this interesting problem:

    This problem was asked in a 1901 issue of the NY Times. Link
  4. May 20, 2010 #3


    User Avatar
    Gold Member

    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.

  5. May 20, 2010 #4
    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook