How does a skeleton watch work?

Answer 1

A Skeleton watch works much like watches used to work in the older times 19th century and beyond, that is to say that they must be constantly wound. The way non-batter powered watches work is quite simple. A circular spring, constructed by taking a ridged, yet malleable material, is twisted in a flat spiral. As the spring is wound tighter and tighter, the spring stores potential energy, as seen by Hooke's Law (PE = 1/2kX^2), where K is the spring constant (how ridged the material is), and X is the elongation or compression of the spring. Once the spring is "wound" and is storing Potential Energy, the spring naturally wants to return to equilibrium (its unwound position). Using Conservation of Energy KEi+PEi = KEf+PEf, All of the spring's potential energy will be turned into Kinetic Energy. The Kinetic Energy is naturally "motion" or "velocity", so this is what causes the gears inside the watch to turn. One small gear oscillates (moves back and forth) usually in increments of .5 sec to 1 sec based on the watchmaker. This gear is what moves the "second hand" of the watch. This gear is then attached to another gear with 60 "teeth", therefore, every 60 seconds moves the gear one revolution, which moves another gear 1 "tooth". This latest gear will move the "minute hand" 1 minute or "tooth". The same applies to the hour hand which has 12 teeth for 12 hours. How the skeleton watch stays powered is covered in the next section

The back of a skeleton watch has a weighted semicircle or "counterweight", which works much like a socket wrench. That is to say, the weight can only move in one direction, usually counterclockwise. While is may slide backwards at some points, once it reaches a certain position, usually 1/5 of a revolution or greater, the weight will lock and be only able to move counterclockwise. Because the natural motion of your body (your arm) is to sway or swing from your shoulder, this causes the weight to constantly travel in a counterclockwise fashion. As this weight continues its revolution, it is attached to the center of the spring. Therefore, the weight's motion is what "winds" the spring and stores potential energy. In conclusion, a skeleton watch functions similar to old fashioned watches, because the must be wound. These watches are wound by the motion o your body, that is to say Kinetic Energy of your body --> Potential Energy of the Spring --> Kinetic Energy of watch.

-Matthew Schneider

University of Michigan

Mechanical Engineering Department