PURPOSE: To demonstrate resonance and normal modes.

DESCRIPTION: After starting one of the pendula into motion in the plane of the picture, the motion couples back and forth between the two physical pendula at a rate determined by the spring constant and its location. Coupling can be varied by sliding the spring clamps along the pendula shafts. Normal modes can be nicely demonstrated.

SUGGESTIONS: See Question of the Week #241 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA 3A70.27) See Demonstration Reference File for derivation of the equations.

EQUIPMENT: Mounted spring-coupled physical pendula.

SETUP TIME: None.