TwinTree Insert

02-05 Resonance

esonance on the nuclear scale is somewhat analogous to mechanical re­so­nance. It is a response of an object or system that vibrates in step or phase.

A glass can be broken by the voice of a singer or a bridge can oscillate and col­lap­se when the marching rhythm of a column of soldiers or the undulation cau­sed by strong winds correspond to its own structural resonance frequency, such as the Ta­co­ma Nar­rows Bridge across the Pudget Sound (Figure 02-08).

This correspondence of frequencies allows energy to be transferred from the ex­ter­nal world (the soldiers' legs) to a given physical system (the bridge).

Similarly, a resonance phenomenon will occur when an electromagnetic wave of ap­pro­pri­ate frequency (equal to the Larmor frequency) reaches the nuclei; then, nuclei lo­ca­ted in the state of lower energy will be transferred to the state of higher energy.

Figure 02-08:
The collapse of the Tacoma Narrows Brid­ge across the Pudget Sound in Washington state (U.S.A.) in November 1940 was caused by high winds making the structure os­cil­la­te. Resonance can con­tr­ibu­te to such ac­ci­dents.

Watch a newsreel movie of this incident.

Newsreel (video in mp4):
The Tacoma Bridge Disaster. The 1.9 kilometers long Tacoma Narrows Bridge (called Galloping Gertie) was the first suspension bridge across the Pudget Sound, connecting the Olympic Peninsula with the mainland of Washington state. Four months after its opening, on the morning of 7 November 1940, in a wind bet­ween 65 and 75 kilometers per hour the bridge went into a series of tor­si­o­nal os­cil­la­tions which passed into the bridge's natural resonance frequency. The amplitude stea­di­ly increased until the bridge span broke up.