S.H.M. (Wilberforce Pendulum)

There are two setups available, one is pre-assembled (yellow bob) and the other requires assembly (brass adjustable bob)

A wilberforce pendulum is a pendulum that hangs from a spring. The moment of inertia of the pendulum bob is adjusted so that the rotational frequency is approximately equal to the transitional frequency. When the system is adjusted properly the energy of the pendulum flows back and forth between the two modes, transitional and rotational. The two normal modes have almost equal frequencies, so the beat frequency between the normal modes is much less than the average frequency of the two modes. For this reason the exchange of energy between the two degrees is slow enough to be easily observed. The Wilberforce is also a very good demonstration of neutrino oscillations. 

Setup for the brass Wilberforce pendulum: 
1. There are three adjustable masses on the pendulum bob. 
2. Addjust the two front/side masses to be roughly 2.5mm (2010 update: more like 2.7cm) apart from center. 
3. Make very small adjustments to the back mass either by moving it closer or further from the center. 
4. When the masses have been correctly adjusted you should notice very little transitional movement when the bob is rotating. It is important that the pendulum does not swing from side to side when making adjustments. 

To operate, pull spring down and release 

The Wilberforce spring can undergo two types of harmonic motion. It can oscillate up and down in which case the period should depend only on the type of spring used and the total mass on the end of the spring. The other type of oscillation is rotational vibration. The period of the rotational vibration depends on the type of spring and on the moment of inertia of the mass on the end of the spring.