Benvenuti in queste pagine dedicate a scienza ed arte. Amelia Carolina Sparavigna

Monday, December 27, 2010

The Wilberforce pendulum

A Wilberforce pendulum, invented by Lionel Robert Wilberforce around 1896, consists of a mass suspended by a  helical spring and free to turn on its vertical axis, twisting the spring. Despite the name, this pendulum does not swing back and forth as the Galileo's pendulum does. The mass usually has symmetric pairs of radial 'arms' sticking out horizontally, with small weights on them. These small masses are used to tune the moment of inertia and then the torsional vibration period of the pendulum.
Look the movie1 or movie2 .When correctly adjusted and set in motion, it exhibits a curious motion. One is the familiar up and down bounce of the spring, the other is the twist causing the mass to rotate. Note that the  energy is transferred from pure up and down to pure rotational and back again (coupled mechanical oscillator).  in which periods of purely rotational oscillation gradually alternate with periods of purely up and down oscillation. That is, the energy stored in the device shifts between  'up and down' and  'clockwise and counterclockwise' oscillations.

A little bit of theory: http://online.redwoods.cc.ca.us/instruct/darnold/deproj/sp04/stevemisay/Project1.pdf