# kinetic energy generated by watches! **URL:** \ **Category:** Factual Questions\ **Created:** [November 7, 2003, 6:15am UTC](https://boards.straightdope.com/t/kinetic-energy-generated-by-watches/211843 "2003-11-07T06:15:24Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![jamesb333](https://avatars.discourse-cdn.com/v4/letter/j/e47c2d/32.png) [@jamesb333](https://boards.straightdope.com/u/jamesb333)\ **Post date:** [November 7, 2003, 6:15am UTC](https://boards.straightdope.com/t/kinetic-energy-generated-by-watches/211843/1 "2003-11-07T06:15:24Z")
How do kinetic watches work exactly? More importantly, precisely how much energy can such a mechanism produce 😕 ---
**Author:** ![swansont](https://avatars.discourse-cdn.com/v4/letter/s/5fc32e/32.png) [@swansont](https://boards.straightdope.com/u/swansont)\ **Post date:** [November 7, 2003, 11:36am UTC](https://boards.straightdope.com/t/kinetic-energy-generated-by-watches/211843/2 "2003-11-07T11:36:27Z")
[here is a link](http://howstuffworks.lycoszone.com/question285.htm) Basically it’s an unbalanced mass on a pivot within the watch. Ballpark back-of-the-envelope calculation: If we assume the mass is 10 grams, and you are swinging your arm once a second for 8 hours with a height difference of 10 cm, and the mechanism is 100% efficient at storing the energy, that comes to a whopping 280 joules of energy. Your mileage may vary. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 7, 2003, 11:46am UTC](https://boards.straightdope.com/t/kinetic-energy-generated-by-watches/211843/3 "2003-11-07T11:46:03Z")
I seem to remember some talk a while back about a piezoelectric fabric that could be used to make clothing that would generate enough electricity to run wearable computers and the like - anyone remember this or did I dream it? ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [November 7, 2003, 11:47am UTC](https://boards.straightdope.com/t/kinetic-energy-generated-by-watches/211843/4 "2003-11-07T11:47:11Z")
Assuming that **swansont** ’s 280 J figure is correct, then to put it into perspective it’s enough to power: - a 2000 W oven for 0.14 seconds - a 100 W light bulb for 2.8 seconds - a 15 W refigerator bulb for 18.7 seconds. It’s also enough to run a mechanical watch for a few days. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [November 7, 2003, 11:52am UTC](https://boards.straightdope.com/t/kinetic-energy-generated-by-watches/211843/5 "2003-11-07T11:52:31Z")
> [@](#): > > \*Originally posted by Mangetout \* > \*\*I seem to remember some talk a while back about a piezoelectric fabric that could be used to make clothing that would generate enough electricity to run wearable computers and the like - anyone remember this or did I dream it? \*\* It crops up from time to time. A piezo suit ain’t gonna power your laptop. It’ll power your calculator, maybe even your palm pilot. But so will a battery that’ll cost a few bucks and last for months. Guess which option people will take. ---
**Author:** ![jamesb333](https://avatars.discourse-cdn.com/v4/letter/j/e47c2d/32.png) [@jamesb333](https://boards.straightdope.com/u/jamesb333)\ **Post date:** [November 10, 2003, 6:10am UTC](https://boards.straightdope.com/t/kinetic-energy-generated-by-watches/211843/6 "2003-11-10T06:10:28Z")
Swansont, I appreciate your reply, and the link/info was interesting. But I was wondering about kinetic watches, which differ from the self winding “automatic” watches that use a spring - which is what your link leads to. My understanding so far is that kinetic watches use a weight that somehow transfers energy to a capacitor, but there is no spring. They can keep a charge for up to 6 months… Does anyone know the mechanism behind kinetic watches, and more importantly just how much energy they produce? enough to run a pda? a cellphone? only a watch? [jamesb@seductive.com](mailto:jamesb@seductive.com)😕 ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [November 10, 2003, 7:13am UTC](https://boards.straightdope.com/t/kinetic-energy-generated-by-watches/211843/7 "2003-11-10T07:13:40Z")
It’s the same principle. When you move your arm you move an unbalanced weight in the watch. In the case of an electronic kinetic watch, the unbalanced weight is connected to a generator instead of a spring. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [November 10, 2003, 2:39pm UTC](https://boards.straightdope.com/t/kinetic-energy-generated-by-watches/211843/8 "2003-11-10T14:39:23Z")
> [@](#): > > \*Originally posted by jamesb333 \* > \*\*Swansont, I appreciate your reply, and the link/info was interesting. But I was wondering about kinetic watches, which differ from the self winding “automatic” watches that use a spring - which is what your link leads to. My understanding so far is that kinetic watches use a weight that somehow transfers energy to a capacitor, but there is no spring. They can keep a charge for up to 6 months… > > Does anyone know the mechanism behind kinetic watches, and more importantly just how much energy they produce? enough to run a pda? a cellphone? only a watch?\*\* [How Seiko kinetic watches work.](http://www.seiko-kinetic-watches.com/seiko_kinetic_watches_wk.htm) ---
**Author:** ![Phage](https://avatars.discourse-cdn.com/v4/letter/p/a4c791/32.png) [@Phage](https://boards.straightdope.com/u/Phage)\ **Post date:** [November 10, 2003, 3:15pm UTC](https://boards.straightdope.com/t/kinetic-energy-generated-by-watches/211843/9 "2003-11-10T15:15:46Z")
According to **astro** ’s link, Seiko watches work in the same way except that the energy is not stored in a spring, but converted to an electric charge and stored in a “Seiko kinetic energy unit”. I am guessing that is a capacitor. The rest of the watch is then a regular quartz watch with step motors and the like. I am guessing that the claim the capacitor can hold a charge for 6 months is in a case where it is not being discharged. I would like to draw your attention to the fact that “kinetic” refers to motion, which makes **Swansont** ’s link correct because it describes the same method of generating power. As to how much power it produces, it would be the same as would be generated by a watch with a spring, except probably less because of the conversion of energy types.