How do kinetic watches work?

29 April 2012

Part of the show Is there such a thing as a "girls' throw"?

Question

Hi Chris

Just listened to your podcast on Circadian Rhythms - excellent as always - which led me to wonder about the kinetic watch on my wrist.

I don't need to wind it nor replace batteries. I understand that this is because my wrist moves about so much during the day that that is enough energy to keep the watch going, but how exactly does that work?

Thanks as always.

Regards
Neil

Answer

Dave - If you have ever taken a cup of coffee or something with some foam on the top and spun the cup, the coffee stays still, but the cup turns around. This is based on the same principles. There are some weights inside the watch which are free to move and as you move your wrist around, the weights tend to stay still when your wrist is moving, and so they move around and spin around as you move around, and go through your daily life. This relative movement between the weight and the watch is connected to a little generator via some gears and cogs, and that charges the battery. And so, as long as you keep using it and moving around, it will charge the battery up and it should keep going.